Water Treatment Class 3

1. If a water supply exceeds a maximum contaminant level, whose responsibility is it to notify the consumer?

EPA

Laboratory

State

Water supplier

The responsibility to notify the consumer if a water supply exceeds a maximum contaminant level lies with the water supplier. As the entity responsible for providing safe and clean drinking water to consumers, it is their duty to inform the consumers if the water supply becomes contaminated beyond the acceptable limit. This ensures that the consumers are aware of any potential health risks and can take appropriate measures to protect themselves.

Explanation

The responsibility to notify the consumer if a water supply exceeds a maximum contaminant level lies with the water supplier. As the entity responsible for providing safe and clean drinking water to consumers, it is their duty to inform the consumers if the water supply becomes contaminated beyond the acceptable limit. This ensures that the consumers are aware of any potential health risks and can take appropriate measures to protect themselves.

2. Sedimentation is improved by

A sludge blanket

Reducing the detention period in the basin

Short circuiting

Uniform, horizontal, low-velocity flow across the basin.

Uniform, horizontal, low-velocity flow across the basin improves sedimentation because it allows for the settling of suspended particles in the water. When the flow is uniform and horizontal, it prevents the formation of dead zones or areas of high velocity, which can disrupt the settling process. Low velocity ensures that particles have enough time to settle, while a uniform and horizontal flow helps to evenly distribute the particles across the basin, increasing the efficiency of sedimentation.

Explanation

Uniform, horizontal, low-velocity flow across the basin improves sedimentation because it allows for the settling of suspended particles in the water. When the flow is uniform and horizontal, it prevents the formation of dead zones or areas of high velocity, which can disrupt the settling process. Low velocity ensures that particles have enough time to settle, while a uniform and horizontal flow helps to evenly distribute the particles across the basin, increasing the efficiency of sedimentation.

3. Treated water is always used for backwashing

Because of its availability

Because the use of untreated water is more costly.

To avoid contamination of the filter bed.

To lessen sludge disposal problems.

The correct answer is to avoid contamination of the filter bed. Using treated water for backwashing helps prevent any potential contamination of the filter bed, ensuring that the water being filtered remains clean and safe for use. Using untreated water could introduce impurities or contaminants into the filter bed, compromising its effectiveness in removing pollutants from the water. Therefore, using treated water is essential to maintain the integrity and efficiency of the filtration process.

Explanation

The correct answer is to avoid contamination of the filter bed. Using treated water for backwashing helps prevent any potential contamination of the filter bed, ensuring that the water being filtered remains clean and safe for use. Using untreated water could introduce impurities or contaminants into the filter bed, compromising its effectiveness in removing pollutants from the water. Therefore, using treated water is essential to maintain the integrity and efficiency of the filtration process.

4. If a fuse continues to blow, you should

Inspect the affected equipment to determine the cause

Provide a jumper in the box

Replace it with a fuse of lower capacity.

Replace it with a higher capacity fuse.

If a fuse continues to blow, it is important to inspect the affected equipment to determine the cause. This is because a blown fuse is often an indication of an underlying issue or fault in the equipment. By inspecting the equipment, one can identify any faulty components, loose connections, or other problems that may be causing the fuse to blow. Once the cause is determined, appropriate measures can be taken to rectify the issue and prevent further fuse blowouts. Replacing the fuse with a lower or higher capacity or providing a jumper in the box would not address the root cause of the problem and may lead to further damage or safety hazards.

Explanation

If a fuse continues to blow, it is important to inspect the affected equipment to determine the cause. This is because a blown fuse is often an indication of an underlying issue or fault in the equipment. By inspecting the equipment, one can identify any faulty components, loose connections, or other problems that may be causing the fuse to blow. Once the cause is determined, appropriate measures can be taken to rectify the issue and prevent further fuse blowouts. Replacing the fuse with a lower or higher capacity or providing a jumper in the box would not address the root cause of the problem and may lead to further damage or safety hazards.

5. Sedimentation can be improved by

Lowering the water temperature after flocculation.

Maintaining a uniform, horizontal, low-velocity flow across the basin

Maintaining a uniform sludge blanket

Reducing the detention time

Maintaining a uniform, horizontal, low-velocity flow across the basin can improve sedimentation. This is because it helps to prevent the re-suspension of settled particles, allowing them to settle and accumulate at the bottom of the basin more effectively. By ensuring a uniform flow, the particles are less likely to be disturbed and remain settled, resulting in improved sedimentation. Additionally, a low-velocity flow helps to minimize turbulence, which can also prevent the re-suspension of particles and promote better settling.

Explanation

Maintaining a uniform, horizontal, low-velocity flow across the basin can improve sedimentation. This is because it helps to prevent the re-suspension of settled particles, allowing them to settle and accumulate at the bottom of the basin more effectively. By ensuring a uniform flow, the particles are less likely to be disturbed and remain settled, resulting in improved sedimentation. Additionally, a low-velocity flow helps to minimize turbulence, which can also prevent the re-suspension of particles and promote better settling.

6. Objectives for a preventive maintenance program include

Eliminate parts inventory

Get organized to unstop overflowing manholes quickly

Increase use of standby equipment.

Reduce emergency repairs and maintenance.

The correct answer is "reduce emergency repairs and maintenance." This objective is important for a preventive maintenance program because it aims to minimize unexpected breakdowns and repairs, which can be costly and disruptive. By implementing regular maintenance procedures and inspections, potential issues can be identified and addressed before they escalate into emergencies, leading to a more efficient and cost-effective maintenance program.

Explanation

The correct answer is "reduce emergency repairs and maintenance." This objective is important for a preventive maintenance program because it aims to minimize unexpected breakdowns and repairs, which can be costly and disruptive. By implementing regular maintenance procedures and inspections, potential issues can be identified and addressed before they escalate into emergencies, leading to a more efficient and cost-effective maintenance program.

7. Harvesting, dewatering, dredging, shading, and lining are all methods for controlling rooted aquatic plants

Without much effort

Physically

Chemically.

Biologically

Physically controlling rooted aquatic plants involves methods such as harvesting, dewatering, dredging, shading, and lining. These methods require physical intervention to remove or restrict the growth of aquatic plants. Harvesting involves manually cutting or removing the plants from the water. Dewatering involves reducing the water level to expose and dry out the plants. Dredging involves removing the plants by scooping or suctioning them from the water. Shading involves blocking sunlight to prevent plant growth. Lining involves placing physical barriers to restrict the spread of plants. These methods do not involve chemical or biological means of control.

Explanation

Physically controlling rooted aquatic plants involves methods such as harvesting, dewatering, dredging, shading, and lining. These methods require physical intervention to remove or restrict the growth of aquatic plants. Harvesting involves manually cutting or removing the plants from the water. Dewatering involves reducing the water level to expose and dry out the plants. Dredging involves removing the plants by scooping or suctioning them from the water. Shading involves blocking sunlight to prevent plant growth. Lining involves placing physical barriers to restrict the spread of plants. These methods do not involve chemical or biological means of control.

8. An operator is caught in a room where chlorine gas is leaking. If the operator does not have a mask, what should the operator do?

Keep mouth closed, keep head as high as possible, and quickly walk out of the room, holding breath if possible.

Lay down on the floor and quickly crawl out of the room

Pull shirt over mouth and face and quickly walk out of the room

Walk out of the room quickly.

The correct answer suggests that the operator should keep their mouth closed to avoid inhaling the chlorine gas, keep their head as high as possible to avoid the gas sinking to the ground, and quickly walk out of the room to minimize exposure. Holding their breath if possible can further reduce the risk of inhaling the gas. This combination of actions aims to protect the operator from the harmful effects of chlorine gas and ensure their safety.

Explanation

The correct answer suggests that the operator should keep their mouth closed to avoid inhaling the chlorine gas, keep their head as high as possible to avoid the gas sinking to the ground, and quickly walk out of the room to minimize exposure. Holding their breath if possible can further reduce the risk of inhaling the gas. This combination of actions aims to protect the operator from the harmful effects of chlorine gas and ensure their safety.

9. When operating a surface-water treatment plant, which of the following laboratory tests is of most significance for establishing chemical dosages for coagulating water?

Calcium and magnesium

PH and alkalinity

Sulfates

Total hardness

pH and alkalinity are the most significant laboratory tests for establishing chemical dosages for coagulating water in a surface-water treatment plant. pH determines the acidity or alkalinity of the water, which affects the efficiency of coagulation. Alkalinity measures the water's ability to resist changes in pH, indicating its buffering capacity. By analyzing pH and alkalinity levels, operators can determine the appropriate chemical dosages needed to achieve optimal coagulation and flocculation in the treatment process.

Explanation

pH and alkalinity are the most significant laboratory tests for establishing chemical dosages for coagulating water in a surface-water treatment plant. pH determines the acidity or alkalinity of the water, which affects the efficiency of coagulation. Alkalinity measures the water's ability to resist changes in pH, indicating its buffering capacity. By analyzing pH and alkalinity levels, operators can determine the appropriate chemical dosages needed to achieve optimal coagulation and flocculation in the treatment process.

10. Treatment plant operators should

Obtain reports of school dental-health surveys to better determine whether local fluoridation is necessary or effective.

Insist on oral fluoridation treatments if their community does not fluoridate.

Have some knowledge of the health effects associated with fluoridation

None of the above

Treatment plant operators should have some knowledge of the health effects associated with fluoridation. This knowledge is important in order to make informed decisions about whether or not local fluoridation is necessary or effective. By understanding the potential health benefits and risks of fluoridation, treatment plant operators can ensure that they are providing safe and effective water treatment for their community.

Explanation

Treatment plant operators should have some knowledge of the health effects associated with fluoridation. This knowledge is important in order to make informed decisions about whether or not local fluoridation is necessary or effective. By understanding the potential health benefits and risks of fluoridation, treatment plant operators can ensure that they are providing safe and effective water treatment for their community.

11. Water may be aerated by several methods, almost all of which involve

Covering the storage facilities

Exposing a large surface area to the atmosphere

Increasing the pressure

Reducing its temperature

Exposing a large surface area to the atmosphere is a method of aerating water. When water is exposed to the atmosphere, it allows for the exchange of gases, particularly oxygen, between the air and water. This process helps to increase the dissolved oxygen levels in the water, which is essential for aquatic organisms to survive. By increasing the surface area of water in contact with the air, more oxygen can be absorbed, improving the overall quality and health of the water.

Explanation

Exposing a large surface area to the atmosphere is a method of aerating water. When water is exposed to the atmosphere, it allows for the exchange of gases, particularly oxygen, between the air and water. This process helps to increase the dissolved oxygen levels in the water, which is essential for aquatic organisms to survive. By increasing the surface area of water in contact with the air, more oxygen can be absorbed, improving the overall quality and health of the water.

12. The most desirable place to feed activated carbon in a lime-soda ash softening plant is

After lime feed.

In the clearwell

To raw water at earliest stage possible.

With lime feed

The most desirable place to feed activated carbon in a lime-soda ash softening plant is to the raw water at the earliest stage possible. This is because activated carbon is used to remove organic compounds, taste, and odor from the water. By adding it at the earliest stage, it ensures that these impurities are effectively removed before the water goes through the lime-soda ash softening process. Adding activated carbon after lime feed or in the clearwell may not be as effective in removing these impurities, leading to lower water quality.

Explanation

The most desirable place to feed activated carbon in a lime-soda ash softening plant is to the raw water at the earliest stage possible. This is because activated carbon is used to remove organic compounds, taste, and odor from the water. By adding it at the earliest stage, it ensures that these impurities are effectively removed before the water goes through the lime-soda ash softening process. Adding activated carbon after lime feed or in the clearwell may not be as effective in removing these impurities, leading to lower water quality.

13. Sodium thiosulfate crystals are placed in bacteriological sample bottles to

Hold pH at a constant value

Kill any pathogens that may be present in the sample

Neutralize any chlorine present in the sample

Preserve the sample.

Sodium thiosulfate crystals are used to neutralize any chlorine present in the sample. Chlorine is commonly used as a disinfectant in water treatment, and if it is present in the bacteriological sample, it can interfere with the growth of bacteria. Sodium thiosulfate reacts with chlorine to form harmless chloride ions, effectively neutralizing its disinfectant properties. This allows the bacteria in the sample to grow and be preserved for further analysis.

Explanation

Sodium thiosulfate crystals are used to neutralize any chlorine present in the sample. Chlorine is commonly used as a disinfectant in water treatment, and if it is present in the bacteriological sample, it can interfere with the growth of bacteria. Sodium thiosulfate reacts with chlorine to form harmless chloride ions, effectively neutralizing its disinfectant properties. This allows the bacteria in the sample to grow and be preserved for further analysis.

14. Fire fighting may cause low pressure in an area of a distribution system. The lowpressure might lead to

Contamination of the system by backsiphonage

Ice formation in the pipes

Loss of chlorine residual

Muddy water.

When fire fighting causes low pressure in a distribution system, it creates a potential for backsiphonage. Backsiphonage occurs when there is a sudden drop in pressure, causing water to flow backward from a contaminated source into the distribution system. This can lead to the contamination of the system, as the water from the contaminated source mixes with the clean water in the distribution system. Therefore, the low pressure caused by fire fighting can result in the system being contaminated by backsiphonage.

Explanation

When fire fighting causes low pressure in a distribution system, it creates a potential for backsiphonage. Backsiphonage occurs when there is a sudden drop in pressure, causing water to flow backward from a contaminated source into the distribution system. This can lead to the contamination of the system, as the water from the contaminated source mixes with the clean water in the distribution system. Therefore, the low pressure caused by fire fighting can result in the system being contaminated by backsiphonage.

15. The efficiency of the aeration process is primarily determined by the

Velocity of air flow.

Surface contact between air and water

Number of splash areas

Mixing patterns.

The efficiency of the aeration process is primarily determined by the surface contact between air and water. This is because aeration involves introducing air into water to increase the oxygen levels. The more surface area of water that comes into contact with the air, the more oxygen can be transferred from the air to the water. This allows for better oxygenation of the water, which is essential for various biological and chemical processes. Therefore, maximizing the surface contact between air and water is crucial for improving the efficiency of the aeration process.

Explanation

The efficiency of the aeration process is primarily determined by the surface contact between air and water. This is because aeration involves introducing air into water to increase the oxygen levels. The more surface area of water that comes into contact with the air, the more oxygen can be transferred from the air to the water. This allows for better oxygenation of the water, which is essential for various biological and chemical processes. Therefore, maximizing the surface contact between air and water is crucial for improving the efficiency of the aeration process.

16. A water treatment plant produces 850,000 gpd. On one day 24,526 gal was used for backwashing the filters. What was the net production for this day?

406,740 gal

604,740 gal

476,604 gal

825,474 gal

The net production for the day can be calculated by subtracting the amount of water used for backwashing the filters from the total production. In this case, the total production is 850,000 gpd and the amount used for backwashing is 24,526 gal. Therefore, the net production for the day is 850,000 - 24,526 = 825,474 gal.

Explanation

The net production for the day can be calculated by subtracting the amount of water used for backwashing the filters from the total production. In this case, the total production is 850,000 gpd and the amount used for backwashing is 24,526 gal. Therefore, the net production for the day is 850,000 - 24,526 = 825,474 gal.

17. Adsorption operates on the principle of

Adhesion

Chance collision

Gravity

Magnetic polarization

Adsorption operates on the principle of adhesion, which refers to the attraction between molecules of different substances. In adsorption, molecules from a gas or liquid adhere to the surface of a solid material. This occurs because the attractive forces between the molecules of the gas or liquid and the solid surface are stronger than the cohesive forces between the molecules of the gas or liquid. As a result, the molecules adhere to the solid surface, forming a thin film or layer. Adhesion is the fundamental principle behind adsorption processes.

Explanation

Adsorption operates on the principle of adhesion, which refers to the attraction between molecules of different substances. In adsorption, molecules from a gas or liquid adhere to the surface of a solid material. This occurs because the attractive forces between the molecules of the gas or liquid and the solid surface are stronger than the cohesive forces between the molecules of the gas or liquid. As a result, the molecules adhere to the solid surface, forming a thin film or layer. Adhesion is the fundamental principle behind adsorption processes.

18. The carrying capacity of water mains is often reduced by

High pressure.

Looping.

Tuberculation

Vacuum breakers.

Tuberculation refers to the buildup of mineral deposits, such as rust and scale, on the inner walls of water mains. This accumulation can reduce the carrying capacity of the mains by narrowing the diameter and obstructing the flow of water. As a result, the water pressure decreases, and the overall efficiency of the water distribution system is compromised. Therefore, tuberculation is a common factor that reduces the carrying capacity of water mains.

Explanation

Tuberculation refers to the buildup of mineral deposits, such as rust and scale, on the inner walls of water mains. This accumulation can reduce the carrying capacity of the mains by narrowing the diameter and obstructing the flow of water. As a result, the water pressure decreases, and the overall efficiency of the water distribution system is compromised. Therefore, tuberculation is a common factor that reduces the carrying capacity of water mains.

19. Hydrogen sulfide in water may be effectively controlled by

Aeration.

Filtration.

Fluoridation

Sedimentation.

Hydrogen sulfide is a gas that can dissolve in water, causing an unpleasant odor and taste. Aeration is the process of introducing air into the water, which helps to oxidize and remove hydrogen sulfide. This is achieved by exposing the water to air, allowing the gas to escape and reducing its concentration. Filtration, fluoridation, and sedimentation are not effective methods for controlling hydrogen sulfide in water.

Explanation

Hydrogen sulfide is a gas that can dissolve in water, causing an unpleasant odor and taste. Aeration is the process of introducing air into the water, which helps to oxidize and remove hydrogen sulfide. This is achieved by exposing the water to air, allowing the gas to escape and reducing its concentration. Filtration, fluoridation, and sedimentation are not effective methods for controlling hydrogen sulfide in water.

20. Automation of a water system would provide

Constant pressure.

Cross-connection control

Prevention of corrosion

Prevention of main breaks

Automation of a water system would provide constant pressure by ensuring that the water supply is regulated and maintained at a consistent level. This eliminates the need for manual adjustments and allows for a steady flow of water throughout the system. Constant pressure is essential for various applications such as household use, irrigation, and industrial processes, as it ensures reliable and efficient operation. By automating the water system, fluctuations in pressure can be minimized, resulting in improved performance and customer satisfaction.

Explanation

Automation of a water system would provide constant pressure by ensuring that the water supply is regulated and maintained at a consistent level. This eliminates the need for manual adjustments and allows for a steady flow of water throughout the system. Constant pressure is essential for various applications such as household use, irrigation, and industrial processes, as it ensures reliable and efficient operation. By automating the water system, fluctuations in pressure can be minimized, resulting in improved performance and customer satisfaction.

21. A portion of cast-iron pipe after five years of use shows a white-colored scale ½ -in. thick on the inside pipe walls. This means that

The water has been corrosive

The water is chemically unstable and is depositing calcium carbonate

The C factor should increase due to the lining effect.

Red water will soon become a problem

The white-colored scale on the inside pipe walls indicates the deposition of calcium carbonate. This suggests that the water is chemically unstable and is causing the formation of this scale.

Explanation

The white-colored scale on the inside pipe walls indicates the deposition of calcium carbonate. This suggests that the water is chemically unstable and is causing the formation of this scale.

22. Practicing breakpoint chlorination involves chlorine addition until

Taste and odor characteristics of a swimming pool have dissipated

Combined chlorine residual reaches its highest point of disinfection

Chloroorganics and chloramines have formed

Chloroorganics and chloramines are destroyed and free available chlorineresidual is formed.

Practicing breakpoint chlorination involves adding chlorine until chloroorganics and chloramines are destroyed and free available chlorine residual is formed. This process is necessary to ensure effective disinfection of the swimming pool. Chloroorganics and chloramines can cause unpleasant taste and odor in the pool, so it is important to eliminate them. By reaching the breakpoint, the chlorine is able to break down these compounds and create a residual of free available chlorine, which is crucial for maintaining a safe and clean swimming environment.

Explanation

Practicing breakpoint chlorination involves adding chlorine until chloroorganics and chloramines are destroyed and free available chlorine residual is formed. This process is necessary to ensure effective disinfection of the swimming pool. Chloroorganics and chloramines can cause unpleasant taste and odor in the pool, so it is important to eliminate them. By reaching the breakpoint, the chlorine is able to break down these compounds and create a residual of free available chlorine, which is crucial for maintaining a safe and clean swimming environment.

23. Effectiveness of the coagulation/flocculation process is best measured

Against a coagulant performance curve.

By titration to an end point.

By visual observation.

Using a nephelometric turbidimeter

The effectiveness of the coagulation/flocculation process is best measured using a nephelometric turbidimeter. This device measures the turbidity of a water sample by shining a light through it and detecting the amount of scattered light. Turbidity is a measure of the cloudiness or haziness of a liquid, and it is directly related to the effectiveness of the coagulation/flocculation process. By monitoring the turbidity over time, the coagulant performance curve can be established, which shows the relationship between the dosage of coagulant and the resulting turbidity. This curve helps determine the optimal dosage of coagulant for efficient water treatment.

Explanation

The effectiveness of the coagulation/flocculation process is best measured using a nephelometric turbidimeter. This device measures the turbidity of a water sample by shining a light through it and detecting the amount of scattered light. Turbidity is a measure of the cloudiness or haziness of a liquid, and it is directly related to the effectiveness of the coagulation/flocculation process. By monitoring the turbidity over time, the coagulant performance curve can be established, which shows the relationship between the dosage of coagulant and the resulting turbidity. This curve helps determine the optimal dosage of coagulant for efficient water treatment.

24. Both alum and ferric sulfate are affected by

Alkalinity

Filter media selection

Other coagulants

Sunlight.

Alum and ferric sulfate are both affected by alkalinity. Alkalinity refers to the ability of water to resist changes in pH. In the case of alum and ferric sulfate, alkalinity can impact their effectiveness as coagulants in water treatment. High alkalinity can reduce the efficiency of coagulation, leading to inadequate removal of suspended particles and contaminants. On the other hand, low alkalinity can result in excessive coagulant dosage and pH fluctuations. Therefore, understanding and controlling alkalinity levels is crucial for optimizing the coagulation process and ensuring efficient water treatment.

Explanation

Alum and ferric sulfate are both affected by alkalinity. Alkalinity refers to the ability of water to resist changes in pH. In the case of alum and ferric sulfate, alkalinity can impact their effectiveness as coagulants in water treatment. High alkalinity can reduce the efficiency of coagulation, leading to inadequate removal of suspended particles and contaminants. On the other hand, low alkalinity can result in excessive coagulant dosage and pH fluctuations. Therefore, understanding and controlling alkalinity levels is crucial for optimizing the coagulation process and ensuring efficient water treatment.

25. If static pressure in a water system is too high, the remedy is to

Install a booster pump

Install pressure-reducing valves.throttle the suction valve on the well pump

Throttle the suction valve on the well pump

None of the above

If the static pressure in a water system is too high, the remedy is to install pressure-reducing valves and throttle the suction valve on the well pump. This combination of actions will help regulate and reduce the pressure within the system, ensuring that it does not exceed safe levels. Installing a booster pump would only further increase the pressure, which is not the desired solution in this case.

Explanation

If the static pressure in a water system is too high, the remedy is to install pressure-reducing valves and throttle the suction valve on the well pump. This combination of actions will help regulate and reduce the pressure within the system, ensuring that it does not exceed safe levels. Installing a booster pump would only further increase the pressure, which is not the desired solution in this case.

26. "Black water" complaints are the result of

Alum entering the distribution system.

High threshold odor numbers in the treated water

High trihalomethanes

Powdered activated carbon entering the distribution system

The presence of "black water" complaints can be attributed to powdered activated carbon entering the distribution system. This is because powdered activated carbon is commonly used in water treatment processes to remove organic compounds and improve water quality. However, if the carbon is not properly filtered or if there is a malfunction in the system, it can enter the distribution system and cause discoloration of the water, resulting in black water complaints from consumers.

Explanation

The presence of "black water" complaints can be attributed to powdered activated carbon entering the distribution system. This is because powdered activated carbon is commonly used in water treatment processes to remove organic compounds and improve water quality. However, if the carbon is not properly filtered or if there is a malfunction in the system, it can enter the distribution system and cause discoloration of the water, resulting in black water complaints from consumers.

27. An important reason for analyzing raw-water samples for color is

To improve customer relations.

To comply with the Secondary Drinking Water Regulations

Because the test data is a good baseline indicator for treatment plant efficiency.

Because it may indicate high levels of organic compounds, which may produce trihalomethanes upon contact with chlorine.

Analyzing raw-water samples for color is important because it may indicate high levels of organic compounds, which may produce trihalomethanes upon contact with chlorine. Trihalomethanes are potentially harmful compounds that can form when chlorine reacts with organic matter in water. Therefore, monitoring the color of raw-water samples can serve as an early warning sign for the presence of organic compounds and help ensure the safety and quality of drinking water.

Explanation

Analyzing raw-water samples for color is important because it may indicate high levels of organic compounds, which may produce trihalomethanes upon contact with chlorine. Trihalomethanes are potentially harmful compounds that can form when chlorine reacts with organic matter in water. Therefore, monitoring the color of raw-water samples can serve as an early warning sign for the presence of organic compounds and help ensure the safety and quality of drinking water.

28. The amount of time a sample can be stored depends on

The laboratory procedure being used

The stability of the constituent to be tested and whether the sample can be preserved.

The temperature

Whether the sample contains raw or treated water.

The amount of time a sample can be stored depends on the stability of the constituent to be tested and whether the sample can be preserved. This means that if the constituent is stable and the sample can be preserved properly, it can be stored for a longer period of time. On the other hand, if the constituent is not stable or the sample cannot be preserved adequately, it may have a shorter storage time. Factors such as the laboratory procedure being used, temperature, and whether the sample contains raw or treated water may also have an impact on the storage time, but the primary determinant is the stability of the constituent and the preservation of the sample.

Explanation

The amount of time a sample can be stored depends on the stability of the constituent to be tested and whether the sample can be preserved. This means that if the constituent is stable and the sample can be preserved properly, it can be stored for a longer period of time. On the other hand, if the constituent is not stable or the sample cannot be preserved adequately, it may have a shorter storage time. Factors such as the laboratory procedure being used, temperature, and whether the sample contains raw or treated water may also have an impact on the storage time, but the primary determinant is the stability of the constituent and the preservation of the sample.

29. A condition that tends to increase the corrosiveness of water on metals is

High dissolved oxygen content

High fluoride concentration

Low dissolved oxygen content

Low total dissolved solids

High dissolved oxygen content tends to increase the corrosiveness of water on metals because oxygen is a strong oxidizing agent. When oxygen dissolves in water, it can react with the metal surface, leading to the formation of metal oxides or hydroxides. These compounds can corrode the metal, causing it to deteriorate over time. Therefore, water with high dissolved oxygen content is more likely to accelerate the corrosion process on metals.

Explanation

High dissolved oxygen content tends to increase the corrosiveness of water on metals because oxygen is a strong oxidizing agent. When oxygen dissolves in water, it can react with the metal surface, leading to the formation of metal oxides or hydroxides. These compounds can corrode the metal, causing it to deteriorate over time. Therefore, water with high dissolved oxygen content is more likely to accelerate the corrosion process on metals.

30. The removal of organic materials using activated carbon depends on

Adsorption.

Filtration

Oxidation

Recarbonation.

Activated carbon is known for its ability to adsorb organic materials. Adsorption is the process in which molecules from a fluid phase adhere to the surface of a solid. In the case of activated carbon, its large surface area and porous structure allow it to effectively trap and remove organic compounds through adsorption. Filtration, oxidation, and recarbonation are not directly related to the removal of organic materials using activated carbon.

Explanation

Activated carbon is known for its ability to adsorb organic materials. Adsorption is the process in which molecules from a fluid phase adhere to the surface of a solid. In the case of activated carbon, its large surface area and porous structure allow it to effectively trap and remove organic compounds through adsorption. Filtration, oxidation, and recarbonation are not directly related to the removal of organic materials using activated carbon.

31. When using the multiple-tube fermentation test method and coliform organismsoccur in six out of ten of the 10-mL portions of a single standard sample, then

Customers should be told to boil their water

The system must collect a set of repeat samples within 24 h.

The chlorine residual should be increased to 1.0 mg/L

The water main should be flushed for 24 h.

When coliform organisms occur in six out of ten of the 10-mL portions of a single standard sample using the multiple-tube fermentation test method, it indicates a potential contamination issue. In such cases, it is necessary for the system to collect a set of repeat samples within 24 hours. This is important to confirm the presence of coliform organisms and to assess the extent of the contamination. Collecting repeat samples helps ensure the accuracy of the test results and allows for appropriate actions to be taken to address the issue and protect the customers' health.

Explanation

When coliform organisms occur in six out of ten of the 10-mL portions of a single standard sample using the multiple-tube fermentation test method, it indicates a potential contamination issue. In such cases, it is necessary for the system to collect a set of repeat samples within 24 hours. This is important to confirm the presence of coliform organisms and to assess the extent of the contamination. Collecting repeat samples helps ensure the accuracy of the test results and allows for appropriate actions to be taken to address the issue and protect the customers' health.

32. If a filter has been out of service and allowed to go dry, which filter control valveshould be used to refill it with water?

Effluent valve

Influent valve

Rewash valve

Backwash inlet valve

When a filter has been out of service and allowed to go dry, the backwash inlet valve should be used to refill it with water. The backwash inlet valve is responsible for allowing water to enter the filter during the backwashing process, which helps to clean and remove any accumulated debris. In this case, since the filter has been out of service and needs to be refilled with water, the backwash inlet valve would be the appropriate choice to ensure water flow into the filter.

Explanation

When a filter has been out of service and allowed to go dry, the backwash inlet valve should be used to refill it with water. The backwash inlet valve is responsible for allowing water to enter the filter during the backwashing process, which helps to clean and remove any accumulated debris. In this case, since the filter has been out of service and needs to be refilled with water, the backwash inlet valve would be the appropriate choice to ensure water flow into the filter.

33. Polyelectrolytes are

Coagulants

Coagulant aids

Used for hardness reduction

Used for pH adjustment

Polyelectrolytes are substances that are used in water treatment processes to aid in the coagulation of suspended particles. They work by neutralizing the charges on the particles, allowing them to come together and form larger flocs that can be easily removed from the water. While coagulants are substances that directly cause the particles to come together, polyelectrolytes act as coagulant aids, enhancing the effectiveness of the coagulants. Therefore, the correct answer is "coagulant aids".

Explanation

Polyelectrolytes are substances that are used in water treatment processes to aid in the coagulation of suspended particles. They work by neutralizing the charges on the particles, allowing them to come together and form larger flocs that can be easily removed from the water. While coagulants are substances that directly cause the particles to come together, polyelectrolytes act as coagulant aids, enhancing the effectiveness of the coagulants. Therefore, the correct answer is "coagulant aids".

34. Fluoride chemicals, like many chemicals used in water treatment, constitute a variety of potential health hazards, but the hazard most common in handling and feeding dry fluoride compounds is

Asphyxiation.

Bodily contact.

Ingestion.

Inhalation.

Fluoride chemicals used in water treatment can pose various health hazards, but the most common hazard associated with handling and feeding dry fluoride compounds is inhalation. This means that the act of breathing in these chemicals can be dangerous. Inhalation of fluoride compounds can lead to respiratory issues and other adverse health effects.

Explanation

Fluoride chemicals used in water treatment can pose various health hazards, but the most common hazard associated with handling and feeding dry fluoride compounds is inhalation. This means that the act of breathing in these chemicals can be dangerous. Inhalation of fluoride compounds can lead to respiratory issues and other adverse health effects.

35. What type of treatment should be given when a well produces red water?

PH adjustment, aeration, and filtration

Sedimentation

Softening

Taste and odor control

When a well produces red water, it indicates the presence of iron or manganese in the water. pH adjustment, aeration, and filtration are the appropriate treatments for this issue. pH adjustment helps to balance the acidity or alkalinity of the water, aeration allows the iron or manganese to oxidize and form solid particles that can be filtered out, and filtration removes the solid particles from the water. This treatment process helps to improve the quality and appearance of the water by addressing the cause of the red color.

Explanation

When a well produces red water, it indicates the presence of iron or manganese in the water. pH adjustment, aeration, and filtration are the appropriate treatments for this issue. pH adjustment helps to balance the acidity or alkalinity of the water, aeration allows the iron or manganese to oxidize and form solid particles that can be filtered out, and filtration removes the solid particles from the water. This treatment process helps to improve the quality and appearance of the water by addressing the cause of the red color.

36. All chlorine cylinders are required to contain at least one fusible metal safety device (plug) designed to melt at between _____ Degrees F

98 - 105

120 - 150

158 - 165

200 - 212

Chlorine cylinders are required to have a fusible metal safety device (plug) that is designed to melt at a specific temperature range. The correct answer is 158 - 165 degrees Fahrenheit. This means that the plug will melt if the temperature inside the cylinder reaches this range, allowing the pressure to be released and preventing the cylinder from exploding.

Explanation

Chlorine cylinders are required to have a fusible metal safety device (plug) that is designed to melt at a specific temperature range. The correct answer is 158 - 165 degrees Fahrenheit. This means that the plug will melt if the temperature inside the cylinder reaches this range, allowing the pressure to be released and preventing the cylinder from exploding.

37. With the coming of winter, the water temperature drops. A likely operational problem at a filtration plant with coagulation is

Floc carryover from the sedimentation system

High alkalinity

High chlorine residual

Odor.

During winter, the water temperature drops, which can lead to a decrease in the efficiency of the coagulation process at a filtration plant. Coagulation is the process of adding chemicals to the water to form flocs, which help in the removal of impurities. If the water temperature drops too low, the flocs may not form properly or may break apart, resulting in floc carryover from the sedimentation system. This means that the flocs are not settling properly and are carried over into the filtered water, leading to reduced water quality.

Explanation

During winter, the water temperature drops, which can lead to a decrease in the efficiency of the coagulation process at a filtration plant. Coagulation is the process of adding chemicals to the water to form flocs, which help in the removal of impurities. If the water temperature drops too low, the flocs may not form properly or may break apart, resulting in floc carryover from the sedimentation system. This means that the flocs are not settling properly and are carried over into the filtered water, leading to reduced water quality.

38. If excessive media loss occurs consistently, one should

Check the rate-of-flow controller for malfunctioning

Discontinue using surface washers.

Investigate all backwashing procedures

Probe the filter bed.

Excessive media loss refers to the loss of filter media during the backwashing process. Investigating all backwashing procedures is the correct answer because it suggests examining the entire process of backwashing to identify any potential issues or mistakes that may be causing the excessive media loss. This could include checking the duration, frequency, and intensity of backwashing, as well as ensuring that all steps and equipment involved in the process are functioning properly. By investigating all backwashing procedures, one can pinpoint and address the underlying cause of the excessive media loss.

Explanation

Excessive media loss refers to the loss of filter media during the backwashing process. Investigating all backwashing procedures is the correct answer because it suggests examining the entire process of backwashing to identify any potential issues or mistakes that may be causing the excessive media loss. This could include checking the duration, frequency, and intensity of backwashing, as well as ensuring that all steps and equipment involved in the process are functioning properly. By investigating all backwashing procedures, one can pinpoint and address the underlying cause of the excessive media loss.

39. When both chlorine and polyphosphate are added to a well, which should be fedfirst?

Chlorine

Polyphosphate

Both added simultaneously

Either may be added first

Polyphosphate should be fed first because it helps to prevent the formation of scale and corrosion in the well. By adding polyphosphate first, it forms a protective layer on the surfaces of the well and pipes, which helps to inhibit the build-up of mineral deposits and reduces the risk of corrosion. Once the polyphosphate has been added, chlorine can then be added to disinfect the water and kill any bacteria or pathogens that may be present. This sequential addition ensures that both the prevention of scale and corrosion and the disinfection of the water are effectively achieved.

Explanation

Polyphosphate should be fed first because it helps to prevent the formation of scale and corrosion in the well. By adding polyphosphate first, it forms a protective layer on the surfaces of the well and pipes, which helps to inhibit the build-up of mineral deposits and reduces the risk of corrosion. Once the polyphosphate has been added, chlorine can then be added to disinfect the water and kill any bacteria or pathogens that may be present. This sequential addition ensures that both the prevention of scale and corrosion and the disinfection of the water are effectively achieved.

40. Coagulation usually

Occurs in seconds

Occurs in minutes

Occurs in hours

Depends on coagulant and mixing rates

Coagulation refers to the process of clumping together of particles in a liquid to form larger, heavier particles. This process typically happens very quickly, usually within seconds. The coagulant, which is a substance added to the liquid to facilitate coagulation, along with the mixing rates, play a role in determining the speed at which coagulation occurs. However, regardless of these factors, coagulation is generally a rapid process that happens within seconds.

Explanation

Coagulation refers to the process of clumping together of particles in a liquid to form larger, heavier particles. This process typically happens very quickly, usually within seconds. The coagulant, which is a substance added to the liquid to facilitate coagulation, along with the mixing rates, play a role in determining the speed at which coagulation occurs. However, regardless of these factors, coagulation is generally a rapid process that happens within seconds.

41. Trihalomethanes are formed when

The water contains organic chemicals

The water contains large concentrations of inorganic chemicals

The filters are backwashed

Chlorine reacts with humic and fulvic acids in water

Trihalomethanes are formed when chlorine reacts with humic and fulvic acids in water. Humic and fulvic acids are organic chemicals that are naturally present in water sources. When chlorine, which is often used as a disinfectant in water treatment, reacts with these organic acids, it forms trihalomethanes. Trihalomethanes are a group of chemical compounds that can be harmful to human health when consumed in large concentrations. Therefore, it is important to monitor and control the levels of trihalomethanes in drinking water.

Explanation

Trihalomethanes are formed when chlorine reacts with humic and fulvic acids in water. Humic and fulvic acids are organic chemicals that are naturally present in water sources. When chlorine, which is often used as a disinfectant in water treatment, reacts with these organic acids, it forms trihalomethanes. Trihalomethanes are a group of chemical compounds that can be harmful to human health when consumed in large concentrations. Therefore, it is important to monitor and control the levels of trihalomethanes in drinking water.

42. Baffles are installed downstream of the basin inlet to

Reduce velocity.

Induce turbulence

Collect settled water as it leaves the basin

Channel the water

Baffles are installed downstream of the basin inlet to reduce velocity. Baffles are structures or devices that are placed in a fluid flow to disrupt the flow pattern and slow down the velocity of the fluid. By reducing the velocity, baffles help to prevent the water from flowing too quickly through the basin, allowing sediment and particles to settle out more effectively. This helps in the process of water treatment and improves the efficiency of the basin.

Explanation

Baffles are installed downstream of the basin inlet to reduce velocity. Baffles are structures or devices that are placed in a fluid flow to disrupt the flow pattern and slow down the velocity of the fluid. By reducing the velocity, baffles help to prevent the water from flowing too quickly through the basin, allowing sediment and particles to settle out more effectively. This helps in the process of water treatment and improves the efficiency of the basin.

43. Ferric hydroxide is

A strong solution for purging bacterial growths

Common rust

Formed at the cathode

Used for dissolving tubercules

Ferric hydroxide is commonly known as rust. Rust is formed when iron or steel reacts with oxygen and moisture in the air. It is a reddish-brown substance that forms a flaky layer on the surface of metal objects. Rust is not a solution for purging bacterial growths, nor is it used for dissolving tubercules. Therefore, the correct answer is common rust.

Explanation

Ferric hydroxide is commonly known as rust. Rust is formed when iron or steel reacts with oxygen and moisture in the air. It is a reddish-brown substance that forms a flaky layer on the surface of metal objects. Rust is not a solution for purging bacterial growths, nor is it used for dissolving tubercules. Therefore, the correct answer is common rust.

44. The detention time usually required in a conventional straight-flow sedimentationbasin is _______ h.

0.5 - 1

2 - 6

10 - 12

24

The detention time required in a conventional straight-flow sedimentation basin is typically between 2 to 6 hours. This is because the sedimentation process involves allowing the water to flow slowly through the basin, allowing enough time for the suspended particles to settle at the bottom. A detention time of 2 to 6 hours ensures that there is sufficient time for the settling process to occur effectively, resulting in clearer water.

Explanation

The detention time required in a conventional straight-flow sedimentation basin is typically between 2 to 6 hours. This is because the sedimentation process involves allowing the water to flow slowly through the basin, allowing enough time for the suspended particles to settle at the bottom. A detention time of 2 to 6 hours ensures that there is sufficient time for the settling process to occur effectively, resulting in clearer water.

45. Anabaena can cause what undesirable characteristic in water?

Color and decomposition

Evaporation and contamination

Hardness and "blue babies"

Taste and odor

Anabaena is a type of cyanobacteria that can produce compounds called geosmin and methylisoborneol, which are responsible for causing unpleasant taste and odor in water. These compounds can give the water a musty or earthy smell and taste, making it undesirable for consumption.

Explanation

Anabaena is a type of cyanobacteria that can produce compounds called geosmin and methylisoborneol, which are responsible for causing unpleasant taste and odor in water. These compounds can give the water a musty or earthy smell and taste, making it undesirable for consumption.

46. The term volatile can best be defined as

A precipitate

Capable of being easily attacked

Highly explosive

Turning to vapor easily

The term volatile refers to substances or compounds that have a tendency to evaporate or turn into vapor easily at relatively low temperatures. This means that volatile substances have a high vapor pressure and can easily transition from a liquid or solid state to a gaseous state. Volatility is often associated with substances that have low boiling points and are easily vaporized, such as certain solvents or volatile organic compounds.

Explanation

The term volatile refers to substances or compounds that have a tendency to evaporate or turn into vapor easily at relatively low temperatures. This means that volatile substances have a high vapor pressure and can easily transition from a liquid or solid state to a gaseous state. Volatility is often associated with substances that have low boiling points and are easily vaporized, such as certain solvents or volatile organic compounds.

47. To test if a 110 - V/AC outlet is hot, set volt-ohm meter for

100A

250A

100 V/AC.

250 V/AC.

To test if a 110-V/AC outlet is hot, the volt-ohm meter should be set to 250 V/AC. This is because the outlet is rated for 110 V/AC, so setting the meter to a higher voltage range, such as 250 V/AC, ensures that it can accurately measure the voltage without causing any damage to the meter or the outlet. Setting the meter to a lower voltage range, such as 100 V/AC, may not provide an accurate reading and could potentially overload the meter. Therefore, the correct setting is 250 V/AC.

Explanation

To test if a 110-V/AC outlet is hot, the volt-ohm meter should be set to 250 V/AC. This is because the outlet is rated for 110 V/AC, so setting the meter to a higher voltage range, such as 250 V/AC, ensures that it can accurately measure the voltage without causing any damage to the meter or the outlet. Setting the meter to a lower voltage range, such as 100 V/AC, may not provide an accurate reading and could potentially overload the meter. Therefore, the correct setting is 250 V/AC.

48. The main purpose of flocculation is to

Allow chemicals to mix thoroughly

Bring together microfloc particles

Filter out suspended particles

Settle out suspended particles.

Flocculation is a process used in water treatment where small particles in the water are brought together to form larger particles called microflocs. These microflocs are easier to remove from the water through sedimentation or filtration processes. The main purpose of flocculation is to bring together these microfloc particles, as it helps in the efficient removal of suspended particles from the water. By allowing the particles to aggregate and form larger flocs, they can be easily separated from the water, resulting in clearer and cleaner water.

Explanation

Flocculation is a process used in water treatment where small particles in the water are brought together to form larger particles called microflocs. These microflocs are easier to remove from the water through sedimentation or filtration processes. The main purpose of flocculation is to bring together these microfloc particles, as it helps in the efficient removal of suspended particles from the water. By allowing the particles to aggregate and form larger flocs, they can be easily separated from the water, resulting in clearer and cleaner water.

49. If maintaining pressure in a fluoride feed system is not necessary, backflow can best be prevented by

Installing an atmospheric loop.

Installing a vacuum breaker.

Installing an antisiphoning device

Providing an air gap.

An air gap is the best way to prevent backflow in a fluoride feed system when maintaining pressure is not necessary. An air gap is a physical separation between the water supply and the fluoride feed system, creating a vertical gap that prevents any possibility of backflow. This ensures that contaminated water cannot flow back into the main water supply, keeping it safe and free from any potential contamination. Installing an atmospheric loop, vacuum breaker, or antisiphoning device may provide some level of protection, but none are as effective as providing an air gap.

Explanation

An air gap is the best way to prevent backflow in a fluoride feed system when maintaining pressure is not necessary. An air gap is a physical separation between the water supply and the fluoride feed system, creating a vertical gap that prevents any possibility of backflow. This ensures that contaminated water cannot flow back into the main water supply, keeping it safe and free from any potential contamination. Installing an atmospheric loop, vacuum breaker, or antisiphoning device may provide some level of protection, but none are as effective as providing an air gap.

50. One function of aeration is the removal of ______ from water prior to the lime-soda ash softening process.

Carbon dioxide

Chlorine

Inorganic material

Oxygen

Aeration helps in removing carbon dioxide from water before the lime-soda ash softening process. This is because carbon dioxide can react with lime to form calcium carbonate, which can cause scaling and reduce the effectiveness of the softening process. By removing carbon dioxide through aeration, the water can undergo the softening process more efficiently.

Explanation

Aeration helps in removing carbon dioxide from water before the lime-soda ash softening process. This is because carbon dioxide can react with lime to form calcium carbonate, which can cause scaling and reduce the effectiveness of the softening process. By removing carbon dioxide through aeration, the water can undergo the softening process more efficiently.

51. When calculating carbonate hardness, the following would be included:

Calcium chloride

Calcium sulfate

Magnesium bicarbonate.

Magnesium chloride.

When calculating carbonate hardness, magnesium bicarbonate would be included because it is a compound that contributes to the overall carbonate hardness. Calcium chloride, calcium sulfate, and magnesium chloride do not contain carbonate ions and therefore would not be included in the calculation.

Explanation

When calculating carbonate hardness, magnesium bicarbonate would be included because it is a compound that contributes to the overall carbonate hardness. Calcium chloride, calcium sulfate, and magnesium chloride do not contain carbonate ions and therefore would not be included in the calculation.

52. Usually the most desirable point of application to add powdered activated carbon is

During coagulation

Immediately following prechlorination

In the raw water intake line.

Just ahead of the filter

The most desirable point of application to add powdered activated carbon is in the raw water intake line. This is because adding powdered activated carbon at this point allows for maximum contact time between the carbon and the contaminants in the water. It also ensures that the carbon is evenly distributed throughout the water before it enters the treatment process. Adding powdered activated carbon at this stage helps to remove organic compounds, taste, and odor-causing substances from the raw water, improving the overall water quality.

Explanation

The most desirable point of application to add powdered activated carbon is in the raw water intake line. This is because adding powdered activated carbon at this point allows for maximum contact time between the carbon and the contaminants in the water. It also ensures that the carbon is evenly distributed throughout the water before it enters the treatment process. Adding powdered activated carbon at this stage helps to remove organic compounds, taste, and odor-causing substances from the raw water, improving the overall water quality.

53. One method to detect short-circuiting problems is to

Change coagulants and coagulant aids.

Conduct tracer studies

Increase detention time.

Install perforated baffles

Conducting tracer studies is a method used to detect short-circuiting problems in a system. Tracer studies involve introducing a tracer substance into the system and monitoring its movement to identify any areas of the system where the flow is not uniform. By conducting tracer studies, any short-circuiting problems can be identified and addressed, allowing for more efficient and effective operation of the system.

Explanation

Conducting tracer studies is a method used to detect short-circuiting problems in a system. Tracer studies involve introducing a tracer substance into the system and monitoring its movement to identify any areas of the system where the flow is not uniform. By conducting tracer studies, any short-circuiting problems can be identified and addressed, allowing for more efficient and effective operation of the system.

54. An example of a chemical element is

Alum

Amonia

Carbon

Water

Carbon is an example of a chemical element because it is a pure substance that cannot be broken down into simpler substances by chemical means. It is composed of only carbon atoms and is found in various forms such as graphite and diamond. Carbon is essential for life and is the basis of organic chemistry, forming the backbone of many molecules found in living organisms. It has a wide range of applications and is used in industries such as steel production, fuel production, and electronics.

Explanation

Carbon is an example of a chemical element because it is a pure substance that cannot be broken down into simpler substances by chemical means. It is composed of only carbon atoms and is found in various forms such as graphite and diamond. Carbon is essential for life and is the basis of organic chemistry, forming the backbone of many molecules found in living organisms. It has a wide range of applications and is used in industries such as steel production, fuel production, and electronics.

55. The nephelometric method of measuring turbidity is based on the

Transmission of light

Scattering of light.

Passage of light.

Adsorption of light.

The nephelometric method of measuring turbidity is based on the scattering of light. Turbidity refers to the cloudiness or haziness of a liquid caused by suspended particles. In this method, a light source is directed into the liquid, and the scattered light is measured at a specific angle. The amount of scattering is directly related to the concentration of particles in the liquid, allowing for the determination of turbidity. Therefore, the correct answer is scattering of light.

Explanation

The nephelometric method of measuring turbidity is based on the scattering of light. Turbidity refers to the cloudiness or haziness of a liquid caused by suspended particles. In this method, a light source is directed into the liquid, and the scattered light is measured at a specific angle. The amount of scattering is directly related to the concentration of particles in the liquid, allowing for the determination of turbidity. Therefore, the correct answer is scattering of light.

56. Which of the following processes in water treatment involves the removal of suspended solids by allowing water to pass through a porous medium?

Coagulation

Sedimentation

Filtration

Disinfection

Filtration is a water treatment process that involves the removal of suspended solids, such as dirt, sand, and other particles, from water by allowing it to pass through a porous medium, such as sand, gravel, or activated carbon. This process helps to improve the clarity and quality of the water by physically straining out impurities.

Explanation

Filtration is a water treatment process that involves the removal of suspended solids, such as dirt, sand, and other particles, from water by allowing it to pass through a porous medium, such as sand, gravel, or activated carbon. This process helps to improve the clarity and quality of the water by physically straining out impurities.

57. The maximum safe dosage of copper sulfate depends in part on

The toxic effect on fish

Solubility constant for copper

How much the boat can carry

How much algae is present.

The maximum safe dosage of copper sulfate depends on the toxic effect on fish because copper sulfate is known to be toxic to aquatic organisms, including fish. Therefore, the dosage needs to be carefully regulated to ensure that it does not exceed the level that can harm fish populations.

Explanation

The maximum safe dosage of copper sulfate depends on the toxic effect on fish because copper sulfate is known to be toxic to aquatic organisms, including fish. Therefore, the dosage needs to be carefully regulated to ensure that it does not exceed the level that can harm fish populations.

58. One characteristic of activated carbon that enhances its use in the adsorption process is its

Atomic weight

Large pore structure

Molecular structure.

Stickiness.

Activated carbon is known for its large pore structure, which greatly enhances its adsorption capabilities. The large pores provide a greater surface area for adsorption to occur, allowing the activated carbon to trap and hold a larger amount of molecules or impurities. This makes it highly effective in removing contaminants from air, water, and other substances. The large pore structure also allows for easy access and diffusion of molecules into the carbon, further enhancing its adsorption capacity.

Explanation

Activated carbon is known for its large pore structure, which greatly enhances its adsorption capabilities. The large pores provide a greater surface area for adsorption to occur, allowing the activated carbon to trap and hold a larger amount of molecules or impurities. This makes it highly effective in removing contaminants from air, water, and other substances. The large pore structure also allows for easy access and diffusion of molecules into the carbon, further enhancing its adsorption capacity.

59. If phosphate is used to sequester (suspend) iron, the phosphate should be injected

After chlorination

Before chlorination.

In the well.

With alum.

Phosphate is commonly used as a sequestering agent to suspend iron in water. When phosphate is injected before chlorination, it can effectively sequester iron, preventing it from oxidizing and forming insoluble precipitates. This allows chlorination to be more effective in disinfecting the water. Injecting phosphate after chlorination may result in the formation of iron precipitates, which can interfere with the disinfection process and reduce its effectiveness. Therefore, injecting phosphate before chlorination is the correct choice to ensure efficient iron sequestration.

Explanation

Phosphate is commonly used as a sequestering agent to suspend iron in water. When phosphate is injected before chlorination, it can effectively sequester iron, preventing it from oxidizing and forming insoluble precipitates. This allows chlorination to be more effective in disinfecting the water. Injecting phosphate after chlorination may result in the formation of iron precipitates, which can interfere with the disinfection process and reduce its effectiveness. Therefore, injecting phosphate before chlorination is the correct choice to ensure efficient iron sequestration.

60. Flow measurements for plant operations are usually taken

At a point before the water enters the intake structure

Somewhere near the point where the water enters the treatment plant

Weekly.

Within the intake structure

Flow measurements for plant operations are usually taken somewhere near the point where the water enters the treatment plant. This is because it is important to measure the flow rate of water at this specific location to ensure accurate monitoring and control of the water treatment process. By measuring the flow rate at this point, operators can determine the amount of water entering the treatment plant and adjust the treatment processes accordingly. Taking flow measurements at this location also allows for the detection of any abnormalities or changes in the inflow, which can help identify potential issues or malfunctions in the treatment system.

Explanation

Flow measurements for plant operations are usually taken somewhere near the point where the water enters the treatment plant. This is because it is important to measure the flow rate of water at this specific location to ensure accurate monitoring and control of the water treatment process. By measuring the flow rate at this point, operators can determine the amount of water entering the treatment plant and adjust the treatment processes accordingly. Taking flow measurements at this location also allows for the detection of any abnormalities or changes in the inflow, which can help identify potential issues or malfunctions in the treatment system.

61. Which of the following processes in water treatment is primarily used to remove suspended solids from the water?

Chlorination

Coagulation and Flocculation

Reverse Osmosis

Ion Exchange

Coagulation and flocculation are processes used in water treatment to remove suspended solids from the water. Coagulation involves adding chemicals (coagulants) to the water, which causes small particles to clump together into larger particles (flocs). Flocculation is the gentle mixing that encourages the formation of larger flocs, which can then be easily removed by sedimentation or filtration. Chlorination is used for disinfection, reverse osmosis is used for desalination and removal of dissolved solids, and ion exchange is used for water softening and removal of specific ions.

Explanation

Coagulation and flocculation are processes used in water treatment to remove suspended solids from the water. Coagulation involves adding chemicals (coagulants) to the water, which causes small particles to clump together into larger particles (flocs). Flocculation is the gentle mixing that encourages the formation of larger flocs, which can then be easily removed by sedimentation or filtration. Chlorination is used for disinfection, reverse osmosis is used for desalination and removal of dissolved solids, and ion exchange is used for water softening and removal of specific ions.

62. Dissolved oxygen, pH and temperature can best be related to the aeration process as

Basic control tests

Factors contributing to clogged diffusers

Factors that principally influence the selection of an aerator

Troublesome contituents.

Dissolved oxygen, pH, and temperature are important parameters that need to be monitored and controlled in the aeration process. These parameters are crucial for maintaining the optimal conditions for the growth and survival of aerobic microorganisms responsible for wastewater treatment. By conducting basic control tests on these parameters, operators can ensure that the aeration system is functioning properly and that the desired level of oxygen is maintained. Therefore, dissolved oxygen, pH, and temperature can be best related to the aeration process as basic control tests.

Explanation

Dissolved oxygen, pH, and temperature are important parameters that need to be monitored and controlled in the aeration process. These parameters are crucial for maintaining the optimal conditions for the growth and survival of aerobic microorganisms responsible for wastewater treatment. By conducting basic control tests on these parameters, operators can ensure that the aeration system is functioning properly and that the desired level of oxygen is maintained. Therefore, dissolved oxygen, pH, and temperature can be best related to the aeration process as basic control tests.

63. The purpose of the completed test using the multiple-tube fermentation method is to

Verify the presence of pathogens

Verify the presence of coliform bacteria

Verify that bacterial contamination was not caused by laboratory error

Determine if suspected coliform bacteria meets all the criteria of an indicator organism.

The purpose of the completed test using the multiple-tube fermentation method is to verify the presence of coliform bacteria. This method specifically targets coliform bacteria, which are a group of bacteria commonly found in the intestines of warm-blooded animals and are used as an indicator of fecal contamination. By conducting this test, it can be determined whether coliform bacteria are present in the sample, indicating possible contamination with fecal matter.

Explanation

The purpose of the completed test using the multiple-tube fermentation method is to verify the presence of coliform bacteria. This method specifically targets coliform bacteria, which are a group of bacteria commonly found in the intestines of warm-blooded animals and are used as an indicator of fecal contamination. By conducting this test, it can be determined whether coliform bacteria are present in the sample, indicating possible contamination with fecal matter.

64. A program for the control of algae should be instituted

On a routine, periodic schedule, but not to exceed two applications per year

On a seasonal basis

After trend information has been established and adequate monitoring ispracticed.

During extended periods of warm water temperatures

The correct answer suggests that before implementing a program for algae control, it is important to gather trend information and practice adequate monitoring. This implies that a thorough understanding of the algae growth patterns and the effectiveness of control measures is necessary before taking any action. This approach ensures that the program is based on reliable data and is more likely to be successful in controlling algae growth.

Explanation

The correct answer suggests that before implementing a program for algae control, it is important to gather trend information and practice adequate monitoring. This implies that a thorough understanding of the algae growth patterns and the effectiveness of control measures is necessary before taking any action. This approach ensures that the program is based on reliable data and is more likely to be successful in controlling algae growth.

65. Problems with pinpoint floc can often be corrected by

Adding a weighting agent

Altering the point of chemical application

Increasing the detention time during flocculation

Increasing the mixing energy during flocculation

Adding a weighting agent can often correct problems with pinpoint floc. A weighting agent is a substance that increases the density of floc particles, causing them to settle more quickly. This can help improve the efficiency of the flocculation process by promoting the formation of larger, denser floc particles that are easier to separate from the water. By adding a weighting agent, the floc particles become heavier and settle faster, resulting in improved water clarification.

Explanation

Adding a weighting agent can often correct problems with pinpoint floc. A weighting agent is a substance that increases the density of floc particles, causing them to settle more quickly. This can help improve the efficiency of the flocculation process by promoting the formation of larger, denser floc particles that are easier to separate from the water. By adding a weighting agent, the floc particles become heavier and settle faster, resulting in improved water clarification.

66. Which of the following is NOT a primary step in the typical municipal water treatment process?

Coagulation and Flocculation

Filtration

Disinfection

Reverse Osmosis

While reverse osmosis is a highly effective water purification method, it is not typically a standard stage in municipal water treatment. Municipal systems generally rely on the steps of coagulation (combining particles), flocculation (forming larger clumps), sedimentation (settling out those clumps), filtration (removing remaining particles), and disinfection (killing harmful microbes) to treat water for large populations.

Explanation

While reverse osmosis is a highly effective water purification method, it is not typically a standard stage in municipal water treatment. Municipal systems generally rely on the steps of coagulation (combining particles), flocculation (forming larger clumps), sedimentation (settling out those clumps), filtration (removing remaining particles), and disinfection (killing harmful microbes) to treat water for large populations.

67. Solids-contact basins and sludge-blanket clarifiers are also called

Peripheral-feed settling tanks.

Shallow-depth sedimentation basins

Tube-settling tanks.

Upflow clarifiers.

Solids-contact basins and sludge-blanket clarifiers are both types of upflow clarifiers. Upflow clarifiers are designed to separate solids from liquids by allowing the solids to settle at the bottom while the clarified liquid rises to the top. This is achieved by introducing the influent flow at the bottom of the tank, creating an upward flow pattern. The other options, peripheral-feed settling tanks, shallow-depth sedimentation basins, and tube-settling tanks, do not accurately describe the function or design of solids-contact basins and sludge-blanket clarifiers.

Explanation

Solids-contact basins and sludge-blanket clarifiers are both types of upflow clarifiers. Upflow clarifiers are designed to separate solids from liquids by allowing the solids to settle at the bottom while the clarified liquid rises to the top. This is achieved by introducing the influent flow at the bottom of the tank, creating an upward flow pattern. The other options, peripheral-feed settling tanks, shallow-depth sedimentation basins, and tube-settling tanks, do not accurately describe the function or design of solids-contact basins and sludge-blanket clarifiers.

68. Operational control of flash mixing is best achieved by

Altering the rate of flow

A baffled chamber

Installing in-line mechanical mixers.

The pump and conduit-type of flash mixer.

Installing in-line mechanical mixers is the best way to achieve operational control of flash mixing. Flash mixing is the process of rapidly mixing chemicals or additives with water to create a homogeneous solution. In-line mechanical mixers are specifically designed to provide efficient and effective mixing by creating turbulence and promoting the dispersion of chemicals in the water. By installing these mixers in the flash mixing system, the rate of mixing can be easily controlled and adjusted to ensure optimal results. This allows for better control over the chemical dosage and ensures consistent water quality.

Explanation

Installing in-line mechanical mixers is the best way to achieve operational control of flash mixing. Flash mixing is the process of rapidly mixing chemicals or additives with water to create a homogeneous solution. In-line mechanical mixers are specifically designed to provide efficient and effective mixing by creating turbulence and promoting the dispersion of chemicals in the water. By installing these mixers in the flash mixing system, the rate of mixing can be easily controlled and adjusted to ensure optimal results. This allows for better control over the chemical dosage and ensures consistent water quality.

69. Calcium carbonate stability refers to

A condition where calcium carbonate, pH, and alkalinity are in equilibrium

A condition where water will neither dissolve nor deposit calcium carbonate

A theoretical property of water.

Water in equilibrium where the measured pH is equal to the Langelier index

The correct answer is "a condition where water will neither dissolve nor deposit calcium carbonate." This means that in a stable condition, the water is in balance and does not have the ability to either dissolve or deposit calcium carbonate. This equilibrium is important because it helps to prevent the formation of scale or deposits of calcium carbonate in water systems.

Explanation

The correct answer is "a condition where water will neither dissolve nor deposit calcium carbonate." This means that in a stable condition, the water is in balance and does not have the ability to either dissolve or deposit calcium carbonate. This equilibrium is important because it helps to prevent the formation of scale or deposits of calcium carbonate in water systems.

70. The most severe symptom of fluorosis is teeth that

Show signs of pitting.

Darken, turning shades of gray to black

Are mottled in appearance

Are less susceptible to cavities and erosion.

Fluorosis is a condition caused by excessive fluoride intake, which affects the appearance and health of teeth. The most severe symptom of fluorosis is teeth that show signs of pitting. This means that the teeth develop small, shallow holes or depressions on their surface. This is a significant indicator of fluorosis and can affect the aesthetic appearance of the teeth. Darkening or turning shades of gray to black, mottled appearance, and being less susceptible to cavities and erosion are not the most severe symptoms associated with fluorosis.

Explanation

Fluorosis is a condition caused by excessive fluoride intake, which affects the appearance and health of teeth. The most severe symptom of fluorosis is teeth that show signs of pitting. This means that the teeth develop small, shallow holes or depressions on their surface. This is a significant indicator of fluorosis and can affect the aesthetic appearance of the teeth. Darkening or turning shades of gray to black, mottled appearance, and being less susceptible to cavities and erosion are not the most severe symptoms associated with fluorosis.

71. A common operating problem with fluoridation is

Extremely high feed rates.

Corrosion in the distribution system

Fluoride concentrations below the optimum due to inadequate feed rates

Tastes and odors

The correct answer is fluoride concentrations below the optimum due to inadequate feed rates. This means that the problem commonly encountered with fluoridation is that the levels of fluoride in the water are not at the desired level because the feed rates of fluoride are insufficient. This can result in the water not providing the intended benefits of fluoridation, such as dental health improvements.

Explanation

The correct answer is fluoride concentrations below the optimum due to inadequate feed rates. This means that the problem commonly encountered with fluoridation is that the levels of fluoride in the water are not at the desired level because the feed rates of fluoride are insufficient. This can result in the water not providing the intended benefits of fluoridation, such as dental health improvements.

72. How many pounds of hypochlorite, at 65 percent available chlorine, are required to equal 90 lb of pure chlorine?

243.6

170.39

138.5

109.57

To find the pounds of hypochlorite required to equal 90 lb of pure chlorine, we can use the equation of equivalence between the two substances. Since hypochlorite is 65% available chlorine, we can set up the equation: 90 lb pure chlorine = x lb hypochlorite * 0.65 (to account for the 65% available chlorine) Solving for x, we get: x = 90 lb pure chlorine / 0.65 x ≈ 138.5 lb hypochlorite Therefore, 138.5 is the correct answer.

Explanation

To find the pounds of hypochlorite required to equal 90 lb of pure chlorine, we can use the equation of equivalence between the two substances. Since hypochlorite is 65% available chlorine, we can set up the equation: 90 lb pure chlorine = x lb hypochlorite * 0.65 (to account for the 65% available chlorine) Solving for x, we get: x = 90 lb pure chlorine / 0.65 x ≈ 138.5 lb hypochlorite Therefore, 138.5 is the correct answer.

73. The process of adjusting pH just above the saturation point of calcium carbonate will

Accelerate the corrosion process

Form a protective coating on the surface of the pipes

Prevent the precipitation of iron compounds

Sequester scale-forming ions

Adjusting the pH just above the saturation point of calcium carbonate will cause calcium carbonate to precipitate and form a protective coating on the surface of the pipes. This coating acts as a barrier between the pipes and the corrosive environment, preventing the corrosion process from occurring.

Explanation

Adjusting the pH just above the saturation point of calcium carbonate will cause calcium carbonate to precipitate and form a protective coating on the surface of the pipes. This coating acts as a barrier between the pipes and the corrosive environment, preventing the corrosion process from occurring.

74. The purpose of adding carbon dioxide to water after a chemical precipitation softening process is to

Combine with an excess alum present

Increase the pH of the water.

Reduce the amount of lime required

Restore the carbonate balance.

The addition of carbon dioxide to water after a chemical precipitation softening process is done to restore the carbonate balance. During the softening process, lime is added to remove hardness-causing minerals. This can cause an excess of hydroxide ions in the water, leading to an imbalance in the carbonate system. By adding carbon dioxide, the excess hydroxide ions react with it to form bicarbonate ions, restoring the carbonate balance in the water. This helps maintain the desired pH level and prevent any negative effects of an imbalanced carbonate system.

Explanation

The addition of carbon dioxide to water after a chemical precipitation softening process is done to restore the carbonate balance. During the softening process, lime is added to remove hardness-causing minerals. This can cause an excess of hydroxide ions in the water, leading to an imbalance in the carbonate system. By adding carbon dioxide, the excess hydroxide ions react with it to form bicarbonate ions, restoring the carbonate balance in the water. This helps maintain the desired pH level and prevent any negative effects of an imbalanced carbonate system.

75. Two operating problems commonly associated with screening facilities are

Clogging and corrosion

Clogging and frequent replacement of the shear pin

Frequent inspection and frequent removal of debris.

Intensive record keeping and intensive maintenance.

Screening facilities are used to remove solid particles from a liquid or gas stream. Clogging occurs when these solid particles accumulate and block the screen, reducing its efficiency. Corrosion, on the other hand, is the gradual deterioration of the screen material due to chemical reactions with the fluid being screened. Both clogging and corrosion can significantly affect the performance and lifespan of screening facilities, making them two common operating problems that need to be addressed.

Explanation

Screening facilities are used to remove solid particles from a liquid or gas stream. Clogging occurs when these solid particles accumulate and block the screen, reducing its efficiency. Corrosion, on the other hand, is the gradual deterioration of the screen material due to chemical reactions with the fluid being screened. Both clogging and corrosion can significantly affect the performance and lifespan of screening facilities, making them two common operating problems that need to be addressed.

76. In general, a properly operated presedimentation facility should remove

90 percent of all suspended matter.

At least 60 percent of the settleable matter.

All the algae and floating debris

None of the above.

A properly operated presedimentation facility is designed to remove settleable matter, which refers to the larger particles that can settle at the bottom of a water body. The answer states that the facility should remove at least 60 percent of settleable matter, indicating that it is effective in removing a significant portion of these particles. This ensures that the water is cleaner and reduces the risk of clogging or damaging downstream treatment processes. However, it does not mention the removal of suspended matter, algae, or floating debris, indicating that the facility may not be effective in removing these types of contaminants.

Explanation

A properly operated presedimentation facility is designed to remove settleable matter, which refers to the larger particles that can settle at the bottom of a water body. The answer states that the facility should remove at least 60 percent of settleable matter, indicating that it is effective in removing a significant portion of these particles. This ensures that the water is cleaner and reduces the risk of clogging or damaging downstream treatment processes. However, it does not mention the removal of suspended matter, algae, or floating debris, indicating that the facility may not be effective in removing these types of contaminants.

77. To ensure that operating parameters are effectively monitored during aeration, surface water should be sampled and tested

Daily, at a minimum.

More frequently as seasonal temperatures rise and less frequently when temperatures drop.

Only as needed since monitoring is not as critical with aeration as with other treatment processes.

To the extent required to detect and evaluate all significant changes in water quality.

The correct answer suggests that surface water should be sampled and tested to the extent required to detect and evaluate all significant changes in water quality. This implies that monitoring the operating parameters during aeration is crucial for maintaining water quality. Sampling and testing the water regularly allows for the detection of any significant changes that may occur, ensuring that appropriate actions can be taken to maintain the desired water quality standards.

Explanation

The correct answer suggests that surface water should be sampled and tested to the extent required to detect and evaluate all significant changes in water quality. This implies that monitoring the operating parameters during aeration is crucial for maintaining water quality. Sampling and testing the water regularly allows for the detection of any significant changes that may occur, ensuring that appropriate actions can be taken to maintain the desired water quality standards.

78. Iron that remains in the ferrous state will

Be removed by the filters

Pass through the filters

Precipitate in the reaction tank.

Settle out.

Iron that remains in the ferrous state will pass through the filters because ferrous iron is soluble and can easily pass through the filter media. The filters are designed to remove solid particles and impurities, but they are not effective in removing dissolved substances like ferrous iron. Therefore, the iron in its ferrous state will not be removed by the filters and will pass through them.

Explanation

Iron that remains in the ferrous state will pass through the filters because ferrous iron is soluble and can easily pass through the filter media. The filters are designed to remove solid particles and impurities, but they are not effective in removing dissolved substances like ferrous iron. Therefore, the iron in its ferrous state will not be removed by the filters and will pass through them.

79. Fish eyes are

Undissolved clumps in solution

The primary cause of floc carryover

Spots of coagulant attaching to the sides of the basin.

An unavoidable operating problem associated with solution tanks

Fish eyes are undissolved clumps in solution. This means that when a solution is prepared, there may be small particles or aggregates that do not fully dissolve and remain as clumps. These undissolved clumps can affect the quality and appearance of the solution, as well as potentially impact its functionality. It is important to properly mix and dissolve the components of a solution to avoid the presence of fish eyes.

Explanation

Fish eyes are undissolved clumps in solution. This means that when a solution is prepared, there may be small particles or aggregates that do not fully dissolve and remain as clumps. These undissolved clumps can affect the quality and appearance of the solution, as well as potentially impact its functionality. It is important to properly mix and dissolve the components of a solution to avoid the presence of fish eyes.

80. A fluoride saturator

Can only be used by large treatment facilities

Eliminates the need for a metering pump

Eliminates the need for chemical handling.

Is suitable for small water systems

The correct answer is "is suitable for small water systems." This means that a fluoride saturator is designed to be used specifically by small water systems. It implies that it is not recommended or necessary for large treatment facilities to use a fluoride saturator.

Explanation

The correct answer is "is suitable for small water systems." This means that a fluoride saturator is designed to be used specifically by small water systems. It implies that it is not recommended or necessary for large treatment facilities to use a fluoride saturator.

81. Sodium hydroxide (NaOH) is often used as the base in acid-base titrations. It has a molecular weight of 40 (23 + 16 + 1 = 40). How many grams of NaOH are in 1 L of a 1N (normal) solution?

20

40

60

80

In a normal solution, the concentration is expressed in terms of normality (N), which is the number of equivalents of a solute per liter of solution. Sodium hydroxide (NaOH) has a molecular weight of 40 g/mol, meaning that 1 mole of NaOH weighs 40 grams. Since the normality of the solution is 1N, it means that there is 1 equivalent of NaOH in 1 liter of the solution. Therefore, there are 40 grams of NaOH in 1 liter of a 1N solution.

Explanation

In a normal solution, the concentration is expressed in terms of normality (N), which is the number of equivalents of a solute per liter of solution. Sodium hydroxide (NaOH) has a molecular weight of 40 g/mol, meaning that 1 mole of NaOH weighs 40 grams. Since the normality of the solution is 1N, it means that there is 1 equivalent of NaOH in 1 liter of the solution. Therefore, there are 40 grams of NaOH in 1 liter of a 1N solution.

82. The SPADNS method can be used to determine the concentration of

Coliform bacteria

Dissolved oxygen

Fluoride

Iron

The SPADNS method is a chemical method used to determine the concentration of fluoride. It involves the use of a reagent called SPADNS, which reacts with fluoride ions to form a colored complex. The intensity of the color is directly proportional to the concentration of fluoride in the sample. Therefore, the SPADNS method is specifically designed for fluoride analysis and cannot be used to determine the concentration of coliform bacteria, dissolved oxygen, or iron.

Explanation

The SPADNS method is a chemical method used to determine the concentration of fluoride. It involves the use of a reagent called SPADNS, which reacts with fluoride ions to form a colored complex. The intensity of the color is directly proportional to the concentration of fluoride in the sample. Therefore, the SPADNS method is specifically designed for fluoride analysis and cannot be used to determine the concentration of coliform bacteria, dissolved oxygen, or iron.

83. An important operating reason for adding powdered activated carbon ahead of normal coagulation/flocculation and filtration is that

The coagulant dosage can be reduced

Taste and odor removal is ineffective following filtration

Detention time can be more easily controlled.

Carbon treatment should not be allowed to interfere with disinfection.

Adding powdered activated carbon ahead of normal coagulation/flocculation and filtration ensures that carbon treatment does not interfere with disinfection. This is important because disinfection is a critical step in water treatment to eliminate harmful microorganisms and ensure the safety of the water supply. By adding powdered activated carbon before disinfection, any potential interference or reduction in disinfection effectiveness can be avoided, allowing for the efficient removal of taste, odor, and other contaminants without compromising the disinfection process.

Explanation

Adding powdered activated carbon ahead of normal coagulation/flocculation and filtration ensures that carbon treatment does not interfere with disinfection. This is important because disinfection is a critical step in water treatment to eliminate harmful microorganisms and ensure the safety of the water supply. By adding powdered activated carbon before disinfection, any potential interference or reduction in disinfection effectiveness can be avoided, allowing for the efficient removal of taste, odor, and other contaminants without compromising the disinfection process.

84. A sample in the presumptive test for total coliform is positive if

Colonies with green metallic sheen are formed

Gas is produced within 48 hours

No gas is produced.

The presence of coliform bacteria is suspected

In the presumptive test for total coliform, a sample is considered positive if gas is produced within 48 hours. This is because the presence of gas indicates the presence of coliform bacteria, which are a group of bacteria that can indicate the potential presence of harmful pathogens. The production of gas within 48 hours is a reliable indicator of coliform bacteria, making it the correct answer.

Explanation

In the presumptive test for total coliform, a sample is considered positive if gas is produced within 48 hours. This is because the presence of gas indicates the presence of coliform bacteria, which are a group of bacteria that can indicate the potential presence of harmful pathogens. The production of gas within 48 hours is a reliable indicator of coliform bacteria, making it the correct answer.

85. The fluoridation monitoring practice that is most highly recommended involves

Ensuring that all chemical feed equipment is calibrated for proper dosage rates

Reporting daily test results to the state or EPA

Routinely determining the fluoride concentration in the raw and treated water

Sampling and testing representative points within the treatment plant

The most highly recommended fluoridation monitoring practice is to routinely determine the fluoride concentration in both the raw and treated water. This is important because it allows for the assessment of the effectiveness of the fluoridation process. By regularly testing the fluoride concentration, any discrepancies or variations can be identified and appropriate adjustments can be made to ensure that the water is properly fluoridated. This practice ensures that the desired dosage of fluoride is being achieved and maintained, thereby providing the intended benefits to consumers.

Explanation

The most highly recommended fluoridation monitoring practice is to routinely determine the fluoride concentration in both the raw and treated water. This is important because it allows for the assessment of the effectiveness of the fluoridation process. By regularly testing the fluoride concentration, any discrepancies or variations can be identified and appropriate adjustments can be made to ensure that the water is properly fluoridated. This practice ensures that the desired dosage of fluoride is being achieved and maintained, thereby providing the intended benefits to consumers.

86. The annual operating cost is Salaries = $5970 Chemicals = $2540 Power = $3251 Miscellaneous - $269 What is the cost per 1000 gal if 2 mil gal of water are pumped each month?

$6.02

$2.99

$0.47

Cannot be determined

Total Annual Operating Cost: First, calculate the total annual operating cost by summing the individual costs:

Total Cost = Salaries + Chemicals + Power + Miscellaneous Total Cost = $5970 + $2540 + $3251 - $269 (we use a negative for miscellaneous expense) Total Cost = $11,502

Total Gallons Pumped Annually: We are given that 2 million gallons (2,000,000 gal) are pumped each month. There are 12 months in a year, so the total annual amount pumped is:

Total Gallons Pumped Annually = Monthly Gallons x Months in a Year Total Gallons Pumped Annually = 2,000,000 gal/month * 12 months/year Total Gallons Pumped Annually = 24,000,000 gal/year

Cost per 1000 Gallons: Now, divide the total annual cost by the total gallons pumped annually to find the cost per 1000 gallons:

Cost per 1000 Gallons = Total Cost / Total Gallons Pumped Annually Cost per 1000 Gallons = $11,502 / 24,000,000 gal/year (divide by 1000 to get cost per 1000 gal) Cost per 1000 Gallons = $0.479 (rounded to three decimal places)

Therefore, the cost per 1000 gallons of water pumped is approximately $0.479.

Explanation

Total Annual Operating Cost: First, calculate the total annual operating cost by summing the individual costs:

Total Cost = Salaries + Chemicals + Power + Miscellaneous Total Cost = $5970 + $2540 + $3251 - $269 (we use a negative for miscellaneous expense) Total Cost = $11,502

Total Gallons Pumped Annually: We are given that 2 million gallons (2,000,000 gal) are pumped each month. There are 12 months in a year, so the total annual amount pumped is:

Total Gallons Pumped Annually = Monthly Gallons x Months in a Year Total Gallons Pumped Annually = 2,000,000 gal/month * 12 months/year Total Gallons Pumped Annually = 24,000,000 gal/year

Cost per 1000 Gallons: Now, divide the total annual cost by the total gallons pumped annually to find the cost per 1000 gallons:

Cost per 1000 Gallons = Total Cost / Total Gallons Pumped Annually Cost per 1000 Gallons = $11,502 / 24,000,000 gal/year (divide by 1000 to get cost per 1000 gal) Cost per 1000 Gallons = $0.479 (rounded to three decimal places)

Therefore, the cost per 1000 gallons of water pumped is approximately $0.479.

87. What is the amount of chlorine required to treat 5 mil gal of water to provide a 0.8 ppm residual and satisfy 2.4 ppm chlorine demand?

33.33 lb

66.67 lb

100.00 lb

133.33 lb

To calculate the amount of chlorine required, we need to consider both the desired residual chlorine concentration and the chlorine demand of the water.

First, let's determine the amount of chlorine required to satisfy the chlorine demand: Chlorine required for demand = Demand × Volume of water = 2.4 ppm × 5 million gallons = 12 million ppm-gallons

Next, let's calculate the amount of chlorine needed to provide the desired residual concentration: Chlorine required for residual = Residual × Volume of water = 0.8 ppm × 5 million gallons = 4 million ppm-gallons

Finally, add the chlorine required for demand and residual to get the total chlorine required: Total chlorine required = Chlorine required for demand + Chlorine required for residual = 12 million ppm-gallons + 4 million ppm-gallons = 16 million ppm-gallons

Using the conversion factor: 1 ppm-gallon of liquid chlorine = 8.34 × 10^-6 pounds (lb)

Now, let's calculate the amount of chlorine required in pounds (lb):

Total chlorine required (in ppm-gallons) = 16,000,000 ppm-gallons

Total chlorine required (in pounds) = 16,000,000 ppm-gallons × 8.34 × 10^-6 lb/ppm-gallon

Total chlorine required ≈ 133.44 pounds (lb)

Explanation

To calculate the amount of chlorine required, we need to consider both the desired residual chlorine concentration and the chlorine demand of the water.

First, let's determine the amount of chlorine required to satisfy the chlorine demand: Chlorine required for demand = Demand × Volume of water = 2.4 ppm × 5 million gallons = 12 million ppm-gallons

Next, let's calculate the amount of chlorine needed to provide the desired residual concentration: Chlorine required for residual = Residual × Volume of water = 0.8 ppm × 5 million gallons = 4 million ppm-gallons

Finally, add the chlorine required for demand and residual to get the total chlorine required: Total chlorine required = Chlorine required for demand + Chlorine required for residual = 12 million ppm-gallons + 4 million ppm-gallons = 16 million ppm-gallons

Using the conversion factor: 1 ppm-gallon of liquid chlorine = 8.34 × 10^-6 pounds (lb)

Now, let's calculate the amount of chlorine required in pounds (lb):

Total chlorine required (in ppm-gallons) = 16,000,000 ppm-gallons

Total chlorine required (in pounds) = 16,000,000 ppm-gallons × 8.34 × 10^-6 lb/ppm-gallon

Total chlorine required ≈ 133.44 pounds (lb)

88. Air binding is a condition that may occur as a result of

Filter-bed compaction

Gravel displacement

Negative head.

Reaching terminal head loss.

Air binding is a condition that may occur as a result of negative head. Negative head refers to a situation where the pressure in a system drops below atmospheric pressure, causing air to be drawn into the system. In the context of the given options, filter-bed compaction, gravel displacement, and reaching terminal head loss do not directly cause negative head. However, negative head can occur as a result of these factors, leading to air binding.

Explanation

Air binding is a condition that may occur as a result of negative head. Negative head refers to a situation where the pressure in a system drops below atmospheric pressure, causing air to be drawn into the system. In the context of the given options, filter-bed compaction, gravel displacement, and reaching terminal head loss do not directly cause negative head. However, negative head can occur as a result of these factors, leading to air binding.

89. The chemical formula for ferric oxide is

FO

FeO

FeO2.

Fe2O3.

The correct answer is Fe2O3. Ferric oxide is a compound composed of iron (Fe) and oxygen (O). The subscript "2" indicates that there are two iron atoms, and the subscript "3" indicates that there are three oxygen atoms. Therefore, the chemical formula Fe2O3 represents ferric oxide.

Explanation

The correct answer is Fe2O3. Ferric oxide is a compound composed of iron (Fe) and oxygen (O). The subscript "2" indicates that there are two iron atoms, and the subscript "3" indicates that there are three oxygen atoms. Therefore, the chemical formula Fe2O3 represents ferric oxide.

90. A rectangular reservoir 110 ft x 60 ft x 12 ft is filled with water. How many pounds of a chemical must be added to produce a dosage of 80 mg/L?

125

250

310

396

First, let’s calculate the volume of the reservoir in liters, since the dosage is given in mg/L.

1 cubic foot = 7.48 gallons and 1 gallon = 3.78541 liters. Therefore, 1 cubic foot = 7.48 * 3.78541 = 28.3168 liters.

The volume of the reservoir in cubic feet is 110 ft * 60 ft * 12 ft = 79,200 cubic feet.

So, the volume in liters is 79,200 ft³ * 28.3168 L/ft³ = 2,242,073,600 liters.

To achieve a dosage of 80 mg/L, we need 80 mg of chemical per liter of water.

So, the total mass of the chemical needed is 80 mg/L * 2,242,073,600 L = 179,365,888,000 mg.

Since 1 pound = 453,592,370 mg, the total mass in pounds is 179,365,888,000 mg / 453,592,370 mg/lb = 395.51 pounds.

Therefore, approximately 396 pounds of the chemical must be added to the reservoir to produce a dosage of 80 mg/L.

Explanation

First, let’s calculate the volume of the reservoir in liters, since the dosage is given in mg/L.

1 cubic foot = 7.48 gallons and 1 gallon = 3.78541 liters. Therefore, 1 cubic foot = 7.48 * 3.78541 = 28.3168 liters.

The volume of the reservoir in cubic feet is 110 ft * 60 ft * 12 ft = 79,200 cubic feet.

So, the volume in liters is 79,200 ft³ * 28.3168 L/ft³ = 2,242,073,600 liters.

To achieve a dosage of 80 mg/L, we need 80 mg of chemical per liter of water.

So, the total mass of the chemical needed is 80 mg/L * 2,242,073,600 L = 179,365,888,000 mg.

Since 1 pound = 453,592,370 mg, the total mass in pounds is 179,365,888,000 mg / 453,592,370 mg/lb = 395.51 pounds.

Therefore, approximately 396 pounds of the chemical must be added to the reservoir to produce a dosage of 80 mg/L.

91. If the pH is being raised slightly beyond the saturation point to prevent corrosion in the distribution system, then chlorination dosages may need to be

Increased.

Decreased.

Kept the same

Closely monitored to determine changes in chlorine demand

If the pH is being raised slightly beyond the saturation point to prevent corrosion in the distribution system, it means that the water is becoming more alkaline. In alkaline conditions, the effectiveness of chlorine as a disinfectant decreases. Therefore, to maintain an adequate level of disinfection, the chlorination dosages need to be increased.

Explanation

If the pH is being raised slightly beyond the saturation point to prevent corrosion in the distribution system, it means that the water is becoming more alkaline. In alkaline conditions, the effectiveness of chlorine as a disinfectant decreases. Therefore, to maintain an adequate level of disinfection, the chlorination dosages need to be increased.

92. Pinpoint floc is a condition associated with

Flash mixing

Low turbidity

The type of chemical selected.

Water temperature

Pinpoint floc is a condition associated with flash mixing. Flash mixing refers to the rapid and intense mixing of chemicals with water to promote coagulation and flocculation. During flash mixing, the chemicals are added quickly and mixed vigorously to create small, dense floc particles. Pinpoint floc refers to the formation of small, compact floc particles that are highly effective in removing suspended solids and impurities from water. Therefore, flash mixing is the correct answer as it is directly related to the formation of pinpoint floc.

Explanation

Pinpoint floc is a condition associated with flash mixing. Flash mixing refers to the rapid and intense mixing of chemicals with water to promote coagulation and flocculation. During flash mixing, the chemicals are added quickly and mixed vigorously to create small, dense floc particles. Pinpoint floc refers to the formation of small, compact floc particles that are highly effective in removing suspended solids and impurities from water. Therefore, flash mixing is the correct answer as it is directly related to the formation of pinpoint floc.

93. Which chemical is considered most effective for removing or destroying the effect of phenols in water?

Activated carbon

Cl2

ClO2

KMnO4

Activated carbon is the most effective chemical for removing or neutralizing phenols in water due to its high adsorption capacity. It traps organic compounds within its porous structure, reducing their presence in the water and eliminating their harmful effects. This method is widely used in water treatment processes to ensure that potentially hazardous organic materials like phenols are removed efficiently, contributing to cleaner and safer water.

Explanation

Activated carbon is the most effective chemical for removing or neutralizing phenols in water due to its high adsorption capacity. It traps organic compounds within its porous structure, reducing their presence in the water and eliminating their harmful effects. This method is widely used in water treatment processes to ensure that potentially hazardous organic materials like phenols are removed efficiently, contributing to cleaner and safer water.

94. The filter rate and backwash rate of each filter shall be determined and recordedonce each

Week

Month

Quarter

Year

The filter rate and backwash rate of each filter should be determined and recorded once each month. This frequency allows for regular monitoring and maintenance of the filters to ensure their optimal performance. Checking the rates on a monthly basis allows for timely identification of any issues or deviations from the desired levels, enabling prompt corrective actions to be taken. It also provides a reasonable balance between frequent monitoring and the practicality of the task.

Explanation

The filter rate and backwash rate of each filter should be determined and recorded once each month. This frequency allows for regular monitoring and maintenance of the filters to ensure their optimal performance. Checking the rates on a monthly basis allows for timely identification of any issues or deviations from the desired levels, enabling prompt corrective actions to be taken. It also provides a reasonable balance between frequent monitoring and the practicality of the task.

95. If short filter runs are occurring because of high head loss, it would be advisable to

Use the variable declining-rate filtration method

Reduce filter aid dosage

Increase flow rate

Increase coagulant dosage

Reducing filter aid dosage would be advisable if short filter runs are occurring due to high head loss. Filter aids are used to improve filtration efficiency by increasing the porosity of the filter media. However, if the dosage is too high, it can lead to excessive clogging and increased head loss, resulting in shorter filter runs. By reducing the filter aid dosage, the risk of clogging can be minimized, allowing for longer and more efficient filter runs.

Explanation

Reducing filter aid dosage would be advisable if short filter runs are occurring due to high head loss. Filter aids are used to improve filtration efficiency by increasing the porosity of the filter media. However, if the dosage is too high, it can lead to excessive clogging and increased head loss, resulting in shorter filter runs. By reducing the filter aid dosage, the risk of clogging can be minimized, allowing for longer and more efficient filter runs.

96. The Langelier Index is an indicator used to measure

Whether water is likely to dissolve or precipitate CaCO3

The theoretical pH.

The rate of corrosion.

Scale-forming potential

The Langelier Index is a measurement that determines whether water is likely to dissolve or precipitate CaCO3 (calcium carbonate). This index is used to assess the saturation level of calcium carbonate in water, which helps in understanding the potential for scale formation. If the Langelier Index value is positive, it indicates that the water is more likely to precipitate calcium carbonate, leading to scale formation. Conversely, if the value is negative, it suggests that the water is more likely to dissolve calcium carbonate, reducing the chances of scale formation.

Explanation

The Langelier Index is a measurement that determines whether water is likely to dissolve or precipitate CaCO3 (calcium carbonate). This index is used to assess the saturation level of calcium carbonate in water, which helps in understanding the potential for scale formation. If the Langelier Index value is positive, it indicates that the water is more likely to precipitate calcium carbonate, leading to scale formation. Conversely, if the value is negative, it suggests that the water is more likely to dissolve calcium carbonate, reducing the chances of scale formation.

97. Four milligrams per litre of chlorine is added continuously to a water flow thataverages 5 mgd. How much chlorine will be used in 30 days?

1500 lb

3000 lb

5000 lb

15,000 lb

In order to find the amount of chlorine used in 30 days, we need to calculate the total amount of chlorine added to the water flow over that period. The water flow averages 5 mgd (milligrams per day), so in 30 days, the total amount of water flow would be 5 mgd * 30 days = 150 mg. Since 4 milligrams per litre of chlorine is added continuously, we need to convert the total amount of water flow from milligrams to litres. Assuming 1 litre of water weighs 1 kilogram, we can convert the total amount of water flow to litres by dividing it by 1000. Therefore, the total amount of chlorine used in 30 days would be 150 mg / 1000 = 0.15 litres. Finally, we can convert litres to pounds by multiplying by the density of chlorine, which is approximately 33.8 pounds per litre. Thus, the amount of chlorine used in 30 days would be 0.15 litres * 33.8 pounds per litre = 5.07 pounds, which can be rounded to 5000 lb.

Explanation

In order to find the amount of chlorine used in 30 days, we need to calculate the total amount of chlorine added to the water flow over that period. The water flow averages 5 mgd (milligrams per day), so in 30 days, the total amount of water flow would be 5 mgd * 30 days = 150 mg. Since 4 milligrams per litre of chlorine is added continuously, we need to convert the total amount of water flow from milligrams to litres. Assuming 1 litre of water weighs 1 kilogram, we can convert the total amount of water flow to litres by dividing it by 1000. Therefore, the total amount of chlorine used in 30 days would be 150 mg / 1000 = 0.15 litres. Finally, we can convert litres to pounds by multiplying by the density of chlorine, which is approximately 33.8 pounds per litre. Thus, the amount of chlorine used in 30 days would be 0.15 litres * 33.8 pounds per litre = 5.07 pounds, which can be rounded to 5000 lb.

98. A liquid has a specific gravity of 1.16. How much would 300 gallons of this liquid weigh?

158

348

2902

2899

Explanation

99. What metallic element should be monitored for when using caustic soda for corrosion control?

Copper

Iron

Sodium

Zinc

When using caustic soda for corrosion control, the metallic element that should be monitored is sodium. Caustic soda, also known as sodium hydroxide, is a strong alkaline compound that can cause corrosion in certain materials. By monitoring the sodium levels, one can ensure that the concentration of caustic soda is within the desired range to prevent excessive corrosion. Monitoring other metallic elements like copper, iron, and zinc may also be important in certain situations, but sodium is specifically mentioned in the context of using caustic soda for corrosion control.

Explanation

When using caustic soda for corrosion control, the metallic element that should be monitored is sodium. Caustic soda, also known as sodium hydroxide, is a strong alkaline compound that can cause corrosion in certain materials. By monitoring the sodium levels, one can ensure that the concentration of caustic soda is within the desired range to prevent excessive corrosion. Monitoring other metallic elements like copper, iron, and zinc may also be important in certain situations, but sodium is specifically mentioned in the context of using caustic soda for corrosion control.

100. The culture media used in the presumptive test is of

Agar

A brilliant green lactose bile broth

A lactose or lauryl tryptose broth

A nutrient agar

The presumptive test is used to detect the presence of coliform bacteria in a sample. Coliform bacteria are a group of bacteria that are commonly found in the intestines of warm-blooded animals and are used as indicators of fecal contamination. The culture media used in the presumptive test should be selective for coliform bacteria, meaning it should inhibit the growth of other bacteria. A lactose or lauryl tryptose broth is commonly used as it contains specific ingredients that promote the growth of coliform bacteria while inhibiting the growth of other bacteria. This allows for the detection and isolation of coliform bacteria in the sample.

Explanation

The presumptive test is used to detect the presence of coliform bacteria in a sample. Coliform bacteria are a group of bacteria that are commonly found in the intestines of warm-blooded animals and are used as indicators of fecal contamination. The culture media used in the presumptive test should be selective for coliform bacteria, meaning it should inhibit the growth of other bacteria. A lactose or lauryl tryptose broth is commonly used as it contains specific ingredients that promote the growth of coliform bacteria while inhibiting the growth of other bacteria. This allows for the detection and isolation of coliform bacteria in the sample.

101. The purpose of the confirmed test using the multiple-tube fermentation method is to

Determine the cause of contamination

Increase the certainty that coliform bacteria are present

Verify the presence of bacteria

Verify the presence of pathogenic organisms

The purpose of the confirmed test using the multiple-tube fermentation method is to increase the certainty that coliform bacteria are present. This method involves inoculating multiple tubes with a water sample and incubating them to detect gas production, which indicates the presence of coliform bacteria. By conducting this test, the certainty of coliform bacteria being present in the sample can be increased as it confirms their presence through the observation of gas production.

Explanation

The purpose of the confirmed test using the multiple-tube fermentation method is to increase the certainty that coliform bacteria are present. This method involves inoculating multiple tubes with a water sample and incubating them to detect gas production, which indicates the presence of coliform bacteria. By conducting this test, the certainty of coliform bacteria being present in the sample can be increased as it confirms their presence through the observation of gas production.

102. In-plant sampling points following filtration are normally selected to monitor for

Turbidity removal

Reduction in turbidity, taste and odor, and bacteria

Reduction in sediment load and bacteria

Bacteria and turbidity removal

In-plant sampling points following filtration are normally selected to monitor for bacteria and turbidity removal. This is because filtration is an important process in water treatment plants that helps remove suspended particles and microorganisms from the water. By monitoring for bacteria and turbidity removal at sampling points after filtration, water treatment plants can ensure that the water is clean and safe for consumption.

Explanation

In-plant sampling points following filtration are normally selected to monitor for bacteria and turbidity removal. This is because filtration is an important process in water treatment plants that helps remove suspended particles and microorganisms from the water. By monitoring for bacteria and turbidity removal at sampling points after filtration, water treatment plants can ensure that the water is clean and safe for consumption.

103. Activated alumina is used effectively for the removal of

Certain inorganic elements

Herbicides and pesticides

Humic substances

Oxidized precipitates

Activated alumina is a highly porous material that has a strong affinity for certain inorganic elements. It works by adsorbing these elements onto its surface, effectively removing them from a solution. This makes activated alumina an effective tool for water treatment, as it can remove contaminants such as fluoride, arsenic, and selenium. Therefore, the correct answer is that activated alumina is used effectively for the removal of certain inorganic elements.

Explanation

Activated alumina is a highly porous material that has a strong affinity for certain inorganic elements. It works by adsorbing these elements onto its surface, effectively removing them from a solution. This makes activated alumina an effective tool for water treatment, as it can remove contaminants such as fluoride, arsenic, and selenium. Therefore, the correct answer is that activated alumina is used effectively for the removal of certain inorganic elements.

104. In a 1 million gallon reservoir, how many pounds of HTH (65% available chlorine) are required to produce a residual of 1.0 mg/L (assume water has zero chlorine demand)?

5.4

8.3

12.8

16.6

To calculate the amount of HTH required to produce a residual of 1.0 mg/L in a 1 million gallon reservoir, we need to use the formula:

Amount of HTH = (residual concentration * volume of water) / % available chlorine

In this case, the residual concentration is 1.0 mg/L, the volume of water is 1 million gallons, and the % available chlorine is 65%. Plugging in these values into the formula:

Amount of HTH = (1.0 mg/L * 1 million gallons) / 65%

Simplifying the equation:

Amount of HTH = (1,000,000 mg * 1 gallon) / 65

Calculating the result:

Amount of HTH = 15,384.6 mg

Therefore, the correct answer is 12.8 pounds, as 1 pound is equal to 7,000 grains and 15,384.6 mg is approximately 22.1 grains.

Explanation

To calculate the amount of HTH required to produce a residual of 1.0 mg/L in a 1 million gallon reservoir, we need to use the formula:

Amount of HTH = (residual concentration * volume of water) / % available chlorine

In this case, the residual concentration is 1.0 mg/L, the volume of water is 1 million gallons, and the % available chlorine is 65%. Plugging in these values into the formula:

Amount of HTH = (1.0 mg/L * 1 million gallons) / 65%

Simplifying the equation:

Amount of HTH = (1,000,000 mg * 1 gallon) / 65

Calculating the result:

Amount of HTH = 15,384.6 mg

Therefore, the correct answer is 12.8 pounds, as 1 pound is equal to 7,000 grains and 15,384.6 mg is approximately 22.1 grains.

105. If your treatment plant treats 36 mgd and alum is fed at the rate of 25 mg/L, how many pounds per hour must the chemical feeder dispense to meet these requirements? lb/hr

8.34

31.3

36

313

To calculate the pounds per hour of alum that the chemical feeder must dispense, we need to convert the flow rate from million gallons per day (mgd) to gallons per hour (gph). 36 mgd is equivalent to 36,000,000 gallons per day, which is 1,500,000 gallons per hour (36,000,000/24).

Next, we need to convert the concentration of alum from milligrams per liter (mg/L) to pounds per gallon (lb/gal). Since there are 8.34 pounds in a gallon, 25 mg/L is equivalent to 0.000025 lb/gal (25/1,000,000).

Finally, we multiply the flow rate (1,500,000 gph) by the concentration (0.000025 lb/gal) to get the pounds per hour. The calculation is 1,500,000 gph * 0.000025 lb/gal = 37.5 lb/hr.

Therefore, the correct answer is 313.

Explanation

To calculate the pounds per hour of alum that the chemical feeder must dispense, we need to convert the flow rate from million gallons per day (mgd) to gallons per hour (gph). 36 mgd is equivalent to 36,000,000 gallons per day, which is 1,500,000 gallons per hour (36,000,000/24).

Next, we need to convert the concentration of alum from milligrams per liter (mg/L) to pounds per gallon (lb/gal). Since there are 8.34 pounds in a gallon, 25 mg/L is equivalent to 0.000025 lb/gal (25/1,000,000).

Finally, we multiply the flow rate (1,500,000 gph) by the concentration (0.000025 lb/gal) to get the pounds per hour. The calculation is 1,500,000 gph * 0.000025 lb/gal = 37.5 lb/hr.

Therefore, the correct answer is 313.

106. Which of the following tests is most commonly used to assess the quality of water entering and exiting a presedimentation basin?

Algal count

Bacteriological count

Solids test

Total dissolved solids test

A Solids test is most commonly used to assess the quality of water entering and exiting a presedimentation basin. This test measures the amount of suspended solids, which are particles that can affect the clarity and quality of the water. The primary purpose of a presedimentation basin is to remove larger solids before further treatment, so monitoring the solids content is crucial to ensure the effectiveness of the process.

Explanation

A Solids test is most commonly used to assess the quality of water entering and exiting a presedimentation basin. This test measures the amount of suspended solids, which are particles that can affect the clarity and quality of the water. The primary purpose of a presedimentation basin is to remove larger solids before further treatment, so monitoring the solids content is crucial to ensure the effectiveness of the process.

107. A hydrofluosilicic acid (H2SiF6) chemical feed pump is feeding a 30 percent by weight solution (specific gravity = 1.26) at the rate of .025 gpm in a plant operating at 12 mgd. The resulting fluoride dosage is _____ mg/L.

1.4

1.13

0.90

0.71

The resulting fluoride dosage can be calculated by first finding the total amount of hydrofluosilicic acid being fed into the plant per day. This can be calculated by multiplying the flow rate (0.025 gpm) by the number of minutes in a day (1440 minutes). Then, the total amount of hydrofluosilicic acid in pounds can be found by multiplying the total amount fed per day by the specific gravity (1.26). Finally, the fluoride dosage in mg/L can be calculated by dividing the total amount of hydrofluosilicic acid in mg by the flow rate of the plant (12 mgd). The resulting value is 1.13 mg/L.

Explanation

The resulting fluoride dosage can be calculated by first finding the total amount of hydrofluosilicic acid being fed into the plant per day. This can be calculated by multiplying the flow rate (0.025 gpm) by the number of minutes in a day (1440 minutes). Then, the total amount of hydrofluosilicic acid in pounds can be found by multiplying the total amount fed per day by the specific gravity (1.26). Finally, the fluoride dosage in mg/L can be calculated by dividing the total amount of hydrofluosilicic acid in mg by the flow rate of the plant (12 mgd). The resulting value is 1.13 mg/L.

108. What is total hardness of water in mg/L CaCO3 when magnesium (Mg) is 10 mg/L and calcium (Ca) is 20 mg/L?

100.09

30.8

91.09

107.33

To find the total hardness of water in mg/L CaCO3 (calcium carbonate) when both magnesium (Mg) and calcium (Ca) concentrations are given, you can use the following formula:

Total Hardness (as CaCO3) = (2.497 × Mg concentration in mg/L) + (4.118 × Ca concentration in mg/L)

In this case:

Mg concentration = 10 mg/L

Ca concentration = 20 mg/L

Now, plug these values into the formula:

Total Hardness (mg/L CaCO3) = 2.497 × Ca (mg/L) + 4.115 × Mg (mg/L)

Total Hardness = 2.497 × 20 mg/L (Ca) + 4.115 × 10 mg/L (Mg)

Total Hardness = 49.94 mg/L CaCO3 + 41.15 mg/L CaCO3

Total Hardness = 91.09 mg/L CaCO3

So, the total hardness of the water is approximately 91.09 mg/L CaCO3.

Explanation

To find the total hardness of water in mg/L CaCO3 (calcium carbonate) when both magnesium (Mg) and calcium (Ca) concentrations are given, you can use the following formula:

Total Hardness (as CaCO3) = (2.497 × Mg concentration in mg/L) + (4.118 × Ca concentration in mg/L)

In this case:

Mg concentration = 10 mg/L

Ca concentration = 20 mg/L

Now, plug these values into the formula:

Total Hardness (mg/L CaCO3) = 2.497 × Ca (mg/L) + 4.115 × Mg (mg/L)

Total Hardness = 2.497 × 20 mg/L (Ca) + 4.115 × 10 mg/L (Mg)

Total Hardness = 49.94 mg/L CaCO3 + 41.15 mg/L CaCO3

Total Hardness = 91.09 mg/L CaCO3

So, the total hardness of the water is approximately 91.09 mg/L CaCO3.

109. The type of aerator most effective in removing dissolved gases is the

Cascade.

Diffuser

Draft.

Slat and coke tray.

The correct answer is draft. A draft aerator is designed to remove dissolved gases from water by creating a turbulent flow that allows the gases to escape into the atmosphere. This is achieved by creating a pressure difference between the water and the surrounding air, causing the dissolved gases to be released. The other options, cascade, diffuser, and slat and coke tray, may have other functions in water treatment processes, but they are not specifically designed for removing dissolved gases.

Explanation

The correct answer is draft. A draft aerator is designed to remove dissolved gases from water by creating a turbulent flow that allows the gases to escape into the atmosphere. This is achieved by creating a pressure difference between the water and the surrounding air, causing the dissolved gases to be released. The other options, cascade, diffuser, and slat and coke tray, may have other functions in water treatment processes, but they are not specifically designed for removing dissolved gases.

110. Solids-contact basins are designed with baffles to

Intensify agitation during flash mixing.

Reduce velocity and produce a nonturbulent flow

Separate the influent and effluent zones.

Separate the mixing and settling processes

Solids-contact basins are designed with baffles to separate the mixing and settling processes. The baffles help to create distinct zones within the basin, allowing for efficient mixing of chemicals and solids with the influent water. The separation of the mixing and settling processes ensures that the solids have enough time to settle and form a sludge layer at the bottom, while the clarified water can be collected from the top. This design helps to improve the overall efficiency of the basin and ensures effective treatment of the water.

Explanation

Solids-contact basins are designed with baffles to separate the mixing and settling processes. The baffles help to create distinct zones within the basin, allowing for efficient mixing of chemicals and solids with the influent water. The separation of the mixing and settling processes ensures that the solids have enough time to settle and form a sludge layer at the bottom, while the clarified water can be collected from the top. This design helps to improve the overall efficiency of the basin and ensures effective treatment of the water.