# CA Water Treatment Plant Operator Quiz Chapter 5

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Sedimentation

Water Treatment Plant Operation
Volume 1
Sixth Edition
Please let me know if there are any issues with the quiz such as typos, wrong answers, etc. .

• 1.

### Smooth circular particles will settle slower than irregular particles with ragged edges.

• A.

True

• B.

False

B. False
Explanation
Smooth circular particles will settle faster than irregular particles with ragged edges. This is because the irregular particles have more surface area, which increases the drag and resistance they experience as they settle through a fluid. The smooth circular particles have less surface area, resulting in less drag and faster settling.

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• 2.

### The settling rate (settling velocity) of a particle becomes much slower as the temperature increases.

• A.

True

• B.

False

B. False
Explanation
The settling rate (settling velocity) of a particle actually becomes faster as the temperature increases. This is because as the temperature rises, the viscosity of the fluid decreases, allowing the particle to move more easily through the fluid and settle at a faster rate. Therefore, the statement that the settling rate becomes much slower as the temperature increases is incorrect.

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• 3.

### High winds can have an adverse effect on tube settlers.

• A.

True

• B.

False

A. True
Explanation
High winds can have an adverse effect on tube settlers because they can disrupt the settling process by causing turbulence in the water. This turbulence can prevent the particles from settling properly, reducing the efficiency of the tube settlers in clarifying the water. Additionally, high winds can also cause physical damage to the tube settlers, such as bending or breaking them, further compromising their effectiveness. Therefore, it is true that high winds can have an adverse effect on tube settlers.

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• 4.

### Whenever actual flows in a water treatment plant approach or exceed design flows, problems are likely to develop.

• A.

True

• B.

False

A. True
Explanation
Whenever actual flows in a water treatment plant approach or exceed design flows, problems are likely to develop. This is because the design flows are based on certain parameters and capacities of the plant. When the actual flows exceed these design flows, it can put a strain on the system, leading to potential issues such as reduced efficiency, increased energy consumption, and potential equipment failures. Therefore, it is true that problems are likely to develop when actual flows in a water treatment plant approach or exceed design flows.

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• 5.

### Operators often have trouble visualizing what is happening in an upflow clarifier and become discouraged or upset when routine problems associated with solids-contact units occur.

• A.

True

• B.

False

A. True
Explanation
The statement suggests that operators often struggle to understand the processes taking place in an upflow clarifier, leading to frustration or discouragement when common issues related to solids-contact units arise. This implies that the answer is true, as it confirms the difficulty faced by operators in visualizing and dealing with problems in upflow clarifiers.

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• 6.

### In solids-contact units, a rising flow rate will increase the depth of the slurry and also increase its volume or density.

• A.

True

• B.

False

B. False
Explanation
In solids-contact units, a rising flow rate will increase the depth of the slurry, but it will not necessarily increase its volume or density. The flow rate only affects the depth of the slurry, not its physical properties. Therefore, the statement is false.

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• 7.

### When operating a solids-contact clarification unit, the set of recirculation speeds for warm-weather operation is the same as those used during cold weather.

• A.

True

• B.

False

B. False
Explanation
The explanation for the correct answer "False" is that the recirculation speeds for warm-weather operation are not the same as those used during cold weather when operating a solids-contact clarification unit. The reason for this is that warm weather typically requires higher recirculation speeds to maintain the desired level of solids contact and achieve proper clarification. Cold weather, on the other hand, may require lower recirculation speeds to prevent excessive cooling and maintain optimal operation. Therefore, the set of recirculation speeds for warm-weather operation is different from those used during cold weather.

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• 8.

### Accumulated sludge in the sedimentation basin bottom or sludge sump is periodically removed for further processing (dewatering) and ultimate disposal.

• A.

True

• B.

False

A. True
Explanation
The statement is true because accumulated sludge in the sedimentation basin bottom or sludge sump needs to be periodically removed for further processing and disposal. This is done through a process called dewatering, where the sludge is separated from the water content to reduce its volume and make it easier to handle. Once dewatered, the sludge can be processed further or disposed of in an appropriate manner.

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• 9.

### Changes in raw water quality may be considered a normal condition for many plants and an abnormal condition for other water treatment plants.

• A.

True

• B.

False

A. True
Explanation
This statement suggests that different water treatment plants may have different tolerance levels for changes in raw water quality. What may be considered normal for one plant may be abnormal for another. This implies that there is no universal standard for what is considered normal or abnormal in terms of raw water quality for all water treatment plants. Therefore, the statement is true.

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• 10.

### Significant changes in source water turbidity levels, either increases or decreases, require that operators verify the effectiveness of the sedimentation process n removing suspended solids and floc.

• A.

True

• B.

False

A. True
Explanation
The statement is true because significant changes in source water turbidity levels can affect the effectiveness of the sedimentation process in removing suspended solids and floc. If the turbidity increases, it may indicate higher levels of suspended solids that need to be removed. On the other hand, if the turbidity decreases, it may suggest that the sedimentation process is not effectively removing the suspended solids. Therefore, operators need to verify the effectiveness of the sedimentation process in both scenarios to ensure the water treatment is working properly.

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• 11.

### Results of lab tests are valuable, even if not used.

• A.

True

• B.

False

B. False
Explanation
This statement is false because if lab test results are not used, they are essentially useless. The purpose of conducting lab tests is to gather information and make informed decisions or take appropriate actions based on those results. If the results are not utilized, they hold no value and do not serve any purpose. Therefore, lab test results are only valuable when they are used for their intended purpose.

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• 12.

### The metallic parts of clarifiers and solids-contact units must be protected from corrosion.

• A.

True

• B.

False

A. True
Explanation
The metallic parts of clarifiers and solids-contact units must be protected from corrosion because exposure to water and other chemicals can cause corrosion, which can weaken the metal and lead to equipment failure. To prevent this, protective coatings or materials are often used to create a barrier between the metal and the corrosive substances. This helps to extend the lifespan of the equipment and ensure its proper functioning. Therefore, it is true that the metallic parts of clarifiers and solids-contact units must be protected from corrosion.

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• 13.

### What are the purposes of the sedimentation process?

• A.

To remove grease and reduce the load on the backwashing process

• B.

To remove iron and manganese and to reduce the load on the sludge handling facilities

• C.

To remove pathogens and to reduce the load on the chlorine contact basin

• D.

To remove suspended solids (particles) that are denser (heavier) than water and to reduce the load on the filters

D. To remove suspended solids (particles) that are denser (heavier) than water and to reduce the load on the filters
Explanation
The sedimentation process is used to remove suspended solids (particles) that are denser and heavier than water. These solids settle at the bottom of the sedimentation tank, allowing clear water to be separated and removed from the top. This helps to reduce the load on the filters, as the majority of the larger particles have already been removed.

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• 14.

### Currents in the sedimentation basin are beneficial to what extent?

• A.

That they distribute suspended solids evenly throughout the basin

• B.

That they increase the expected performance of the sedimentation basin

• C.

That they promote flocculation

• D.

That they release floatables to the surface

C. That they promote flocculation
Explanation
The currents in the sedimentation basin promote flocculation. Flocculation is the process of bringing together suspended particles to form larger particles called flocs. This is beneficial because the larger flocs settle more easily and quickly, improving the efficiency of sedimentation. The currents help to mix the particles and promote their aggregation into flocs, enhancing the sedimentation process.

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• 15.

### Why were high-rate or tube settlers developed?

• A.

To eliminate the need for sludge scrapers

• B.

To increase the area required for the sedimentation basin

• C.

To increase the settling efficiency of the conventional rectangular sedimentation basins

• D.

To reduce the effect of winds on sedimentation

C. To increase the settling efficiency of the conventional rectangular sedimentation basins
Explanation
High-rate or tube settlers were developed to increase the settling efficiency of the conventional rectangular sedimentation basins. This means that these settlers help in improving the process of separating solids from liquid in the sedimentation basins. By increasing the settling efficiency, the settlers allow for better removal of suspended solids and improve the overall performance of the sedimentation process.

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• 16.

### What are the major means by which operators can control water treatment processes?

• A.

By adjusting chemicals and chemical feed rates

• B.

• C.

• D.

A. By adjusting chemicals and chemical feed rates
Explanation
Operators can control water treatment processes by adjusting chemicals and chemical feed rates. This is because the addition of chemicals plays a crucial role in treating water and removing impurities. By adjusting the type and amount of chemicals added, operators can optimize the treatment process to achieve desired water quality. Chemical feed rates can be adjusted based on the specific water conditions and treatment objectives. This allows operators to effectively control and maintain the desired water treatment processes.

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• 17.

### Why should solids-contact units be drained periodically?

• A.

To inspect the belt drive

• B.

To inspect the chemical storage facilities

• C.

To inspect the sludge collectors for wear and corrosion

• D.

To inspect the slurry volume

C. To inspect the sludge collectors for wear and corrosion
Explanation
Solids-contact units are used in wastewater treatment plants to separate solids from liquids. Over time, the sludge collectors in these units can wear out or corrode due to the harsh conditions they are exposed to. Draining the units periodically allows operators to inspect the sludge collectors for any signs of wear or corrosion. This helps ensure that the units continue to function properly and prevents any potential issues or failures in the future.

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• 18.

### Why must operators monitor the performance of the sedimentation process?

• A.

In order to anticipate quality or performance changes

• B.

• C.

In order to maintain sludge levels on the bottom of the basin

• D.

In order to meet changing flow demands

A. In order to anticipate quality or performance changes
Explanation
Operators must monitor the performance of the sedimentation process in order to anticipate quality or performance changes. By monitoring the process, operators can identify any deviations or abnormalities that may affect the quality of the treated water or the efficiency of the process. This allows them to take corrective actions in a timely manner and ensure that the desired water quality standards are met. Monitoring also helps in identifying any potential issues or trends that may lead to changes in the performance of the sedimentation process, allowing operators to make necessary adjustments and maintain optimal operation.

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• 19.

### The actual frequency of monitoring the sedimentation process should be based on which factors?

• A.

Environmental conditions and regulatory requirements

• B.

Number of operators and the condition of the training program

• C.

Source of the water supply and variations in the supply

• D.

Temperature of the water and weather conditions

C. Source of the water supply and variations in the supply
Explanation
The frequency of monitoring the sedimentation process should be based on the source of the water supply and variations in the supply. This is because different water sources may have different levels of sedimentation, and the variations in the supply can also affect the sedimentation process. By monitoring these factors, operators can ensure that the sedimentation process is properly managed and adjusted as needed. Environmental conditions, regulatory requirements, number of operators, condition of the training program, temperature of the water, and weather conditions may also be important factors to consider, but they are not directly related to the sedimentation process itself.

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• 20.

### What should the operator do when source water turbidity levels are increasing rapidly?

• A.

Increase the detention time in the upstream impoundment

• B.

Increase the filtration rate through the filters

• C.

Locate the source and implement erosion control practices

• D.

Verify the effectiveness of the coagulant chemicals and the dosage being applied at the flash mixer

D. Verify the effectiveness of the coagulant chemicals and the dosage being applied at the flash mixer
Explanation
When source water turbidity levels are increasing rapidly, the operator should verify the effectiveness of the coagulant chemicals and the dosage being applied at the flash mixer. This is because coagulant chemicals are used to remove turbidity from water by causing particles to clump together and settle out. By checking the effectiveness of the chemicals and the dosage, the operator can ensure that the coagulation process is functioning properly and adjust it if necessary to maintain water quality. This step is important in preventing the turbidity levels from reaching undesirable levels.

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• 21.

### What is required in order to prevent bad laboratory results?

• A.

Constant maintenance and calibration of laboratory equipment and correct lad procedures

• B.

The use of different sample locations and analytical procedures

• C.

Te use of regulatory personnel in collecting the samples and performing laboratory analyses

• D.

Training programs and higher salaries

A. Constant maintenance and calibration of laboratory equipment and correct lad procedures
Explanation
To prevent bad laboratory results, constant maintenance and calibration of laboratory equipment are necessary. This ensures that the equipment is functioning properly and providing accurate measurements. Additionally, correct lab procedures need to be followed to ensure that samples are handled correctly and analyzed accurately. By maintaining and calibrating equipment and following correct procedures, the chances of obtaining bad laboratory results are minimized.

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• 22.

### What are preventive maintenance (P/M) programs designed to ensure? The continued satisfactory operation of treatment plant facilities by

• A.

Avoiding the need for excessive good housekeeping practices

• B.

Maintaining equipment on an as-needed basis when time becomes available

• C.

Purchasing equipment with fewer maintenance requirements

• D.

Reducing the frequency of breakdown failures

D. Reducing the frequency of breakdown failures
Explanation
Preventive maintenance (P/M) programs are designed to reduce the frequency of breakdown failures in treatment plant facilities. By regularly inspecting and maintaining equipment, potential issues can be identified and addressed before they lead to major breakdowns or failures. This helps to ensure the continued satisfactory operation of the facilities and prevents costly downtime and repairs. P/M programs focus on proactive measures to prevent failures rather than relying on reactive measures when equipment breaks down.

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• 23.

### What types of presedimentation facilities are used to reduce the solids-removal load at the water treatment plant?

• A.

Booster pumps

• B.

Debris dams

• C.

Grit basins

• D.

Impoundments

• E.

Intake screens

B. Debris dams
C. Grit basins
D. Impoundments
Explanation
Debris dams, grit basins, and impoundments are all types of presedimentation facilities that are used to reduce the solids-removal load at the water treatment plant. Debris dams are structures that are designed to trap and remove large debris such as branches, leaves, and trash before the water enters the treatment process. Grit basins are used to settle out and remove heavy particles such as sand, gravel, and grit. Impoundments are large reservoirs or ponds where water is stored temporarily, allowing suspended solids to settle out before further treatment. These facilities help to improve the efficiency of the water treatment process by reducing the amount of solids that need to be removed later on.

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• 24.

### What types of currents are found in the typical sedimentation basin?

• A.

Density currents cause by differences in suspended solids concentrations and temperature differences

• B.

Eddy currents produced by the flow of the water coming into and leaving the basin

• C.

Internal currents caused by the movement of microorganisms in the water

• D.

Sludge currents caused by the flow of sludge along the bottom

• E.

Surface currents caused by winds

A. Density currents cause by differences in suspended solids concentrations and temperature differences
B. Eddy currents produced by the flow of the water coming into and leaving the basin
E. Surface currents caused by winds
Explanation
In a typical sedimentation basin, there are multiple types of currents present. Density currents are caused by differences in suspended solids concentrations and temperature differences. Eddy currents are produced by the flow of water entering and leaving the basin. Surface currents are caused by winds. These different types of currents play a role in the sedimentation process and the movement of particles within the basin.

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• 25.

### What are the advantages of an inlet baffle wall?

• A.

Minimize density currents due to temperature differences

• B.

Minimize the tendency of the water to flow at the inlet velocity straight through the basin

• C.

Minimize viscosity changes

• D.

Minimize volumetric flow losses

• E.

Minimize wind currents

A. Minimize density currents due to temperature differences
B. Minimize the tendency of the water to flow at the inlet velocity straight through the basin
E. Minimize wind currents
Explanation
An inlet baffle wall has several advantages. Firstly, it helps minimize density currents caused by temperature differences. This is important because density currents can disrupt the flow and mixing of water in the basin. Secondly, the baffle wall minimizes the tendency of water to flow straight through the basin at the inlet velocity. This ensures that the water is evenly distributed and properly mixed. Additionally, the baffle wall helps minimize wind currents, which can also disrupt the flow patterns in the basin. Overall, the inlet baffle wall helps optimize the performance and efficiency of the system by minimizing density currents, flow tendencies, and wind currents.

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• 26.

### Why may actual flow-through times for different small amounts of water in the same basin vary significantly from the calculated detention time?

• A.

Basin inlet and outlet design

• B.

Effective exchangeable volume (portion of basin through which the water flows)

• C.

Short-circuiting

• D.

Time of day the tests are performed

• E.

Type of dye used in tests

A. Basin inlet and outlet design
B. Effective exchangeable volume (portion of basin through which the water flows)
C. Short-circuiting
Explanation
The actual flow-through times for different small amounts of water in the same basin may vary significantly from the calculated detention time due to several factors. The design of the basin's inlet and outlet can affect the flow rate and cause variations in the actual flow-through times. The effective exchangeable volume, which refers to the portion of the basin through which the water flows, can also impact the flow rate and result in variations. Additionally, short-circuiting, which is the bypassing of water through preferential flow paths, can further contribute to the differences in flow-through times.

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• 27.

### What chemicals can an operator add to water to cause sufficient alkalinity to be present for coagulation?

• A.

Calcium hydroxide (lime)

• B.

Hydrochloric acid (muriatic acid)

• C.

Sodium carbonate (soda ash)

• D.

Sodium hydroxide (caustic soda)

• E.

Sodium hypochlorite (hypochlorite)

A. Calcium hydroxide (lime)
C. Sodium carbonate (soda ash)
D. Sodium hydroxide (caustic soda)
Explanation
Operators can add calcium hydroxide (lime), sodium carbonate (soda ash), and sodium hydroxide (caustic soda) to water in order to increase alkalinity for coagulation. These chemicals help to raise the pH level of the water, which is important for the coagulation process to occur effectively. By increasing alkalinity, these chemicals help to neutralize acidity and create a suitable environment for coagulation to take place.

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• 28.

### When performing the jar test to optimize chemical dosages, operators should duplicate in the jar tester, as nearly as possible, which conditions that occur in the plant?

• A.

Budget

• B.

Chemical dosage

• C.

Detention period

• D.

Iron and manganese

• E.

Mixing speeds

B. Chemical dosage
C. Detention period
E. Mixing speeds
Explanation
When performing the jar test to optimize chemical dosages, operators should duplicate in the jar tester the conditions that occur in the plant regarding chemical dosage, detention period, and mixing speeds. This is important because replicating these conditions allows operators to accurately determine the optimal chemical dosages for the treatment process. By considering the same chemical dosage, detention period, and mixing speeds as in the plant, operators can ensure that the results obtained from the jar test can be effectively applied to the actual treatment process.

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• 29.

### In the normal operation of the sedimentation process, operators should monitor which factors?

• A.

Chlorine residual of the water leaving the sedimentation basin

• B.

Temperature of the entering water

• C.

Temperature of the leaving water

• D.

Turbidity of the water entering the sedimentation basin

• E.

Turbidity of the water leaving the sedimentation basin

B. Temperature of the entering water
D. Turbidity of the water entering the sedimentation basin
E. Turbidity of the water leaving the sedimentation basin
Explanation
In the normal operation of the sedimentation process, operators should monitor the temperature of the entering water, as it can affect the efficiency of the sedimentation process. They should also monitor the turbidity of the water entering and leaving the sedimentation basin, as it indicates the level of particles and impurities in the water. By monitoring these factors, operators can ensure that the sedimentation process is functioning properly and producing clean water.

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• 30.

### Flocs coming over the ends of the sedimentation basin are indicative of which conditions?

• A.

Density currents

• B.

High flows

• C.

Low flows

• D.

Short-circuiting

• E.

Sludge blankets that are too deep

A. Density currents
B. High flows
D. Short-circuiting
E. Sludge blankets that are too deep
Explanation
Flocs coming over the ends of the sedimentation basin can be indicative of density currents, high flows, short-circuiting, or sludge blankets that are too deep. Density currents occur when there is a difference in density between the incoming water and the settled solids, causing the flocs to be carried over the ends. High flows can also cause flocs to be carried over as the sedimentation basin may not be able to handle the increased volume. Short-circuiting refers to the flow of water bypassing the settling zone, allowing flocs to escape. Lastly, if the sludge blankets in the basin are too deep, flocs may be pushed over the ends.

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• 31.

### Which factors could cause changes in source wate alkalinity and pH?

• A.

Decreased rates of sludge removal

• B.

Increased filtration rates

• C.

Spills

• D.

Storms

• E.

Waste discharges

C. Spills
D. Storms
E. Waste discharges
Explanation
Spills, storms, and waste discharges can all cause changes in source water alkalinity and pH. Spills of chemicals or pollutants can introduce substances into the water that can alter its alkalinity and pH levels. Storms can bring in sediment, organic matter, and other materials that can affect the water's chemistry. Waste discharges, such as from industrial or agricultural activities, can release pollutants into the water that can change its alkalinity and pH. These factors can all have significant impacts on the overall water quality and can affect the health of aquatic ecosystems and the suitability of the water for various uses.

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• 32.

### In troubleshooting the sedimentation process, what are possible operator actions when there aresource water quality changes?

• A.

Evaluate overall process performance

• B.

Increase the frequency of process monitoring

• C.

Make appropriate process changes and verify responses

• D.

Perform jar tests if indicated

• E.

Perform necessary analyses to determine the extent of the change

A. Evaluate overall process performance
B. Increase the frequency of process monitoring
C. Make appropriate process changes and verify responses
D. Perform jar tests if indicated
E. Perform necessary analyses to determine the extent of the change
Explanation
When there is a change in resource water quality during the sedimentation process, it is important to evaluate the overall process performance to determine if the change is affecting the efficiency of sedimentation. Increasing the frequency of process monitoring allows for closer observation of any variations and helps in identifying the cause of the change. Making appropriate process changes and verifying the responses ensures that necessary adjustments are made to maintain optimal performance. Performing jar tests, if indicated, helps in understanding the settling characteristics of the sediment and aids in determining the best course of action. Finally, performing necessary analyses helps in determining the extent of the change and its impact on the sedimentation process.

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• 33.

### Which items should be checked after start-up and during normal operation of a sludge pump?

• A.

Excessive noise

• B.

Excessive vibration

• C.

Leakage (water, lubricants)

• D.

Overheating

• E.

Suction and discharge pressures

A. Excessive noise
B. Excessive vibration
C. Leakage (water, lubricants)
D. Overheating
E. Suction and discharge pressures
Explanation
During start-up and normal operation of a sludge pump, several items should be checked to ensure its proper functioning. Excessive noise can indicate mechanical issues or misalignment, while excessive vibration may suggest imbalances or worn-out components. Leakage of water or lubricants can lead to reduced efficiency or damage to the pump. Overheating can be a sign of inadequate cooling or excessive friction. Lastly, monitoring the suction and discharge pressures is crucial to ensure the pump is operating within its design limits and delivering the required flow rate.

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• 34.

### In the normal operation of the sedimentation process, the operator will be expected to perform which routine maintenance functions as a part of an overall preventive maintenance program?

• A.

Check bearing for wear, overheating, and proper lubrication

• B.

Ensure good ventilation (air circulation) in equipment work areas

• C.

Inspect for alignment of shafts and couplings

• D.

Keep electric motors free of dirt and moisture

• E.

Maintain proper lubrication and oil levels

A. Check bearing for wear, overheating, and proper lubrication
B. Ensure good ventilation (air circulation) in equipment work areas
C. Inspect for alignment of shafts and couplings
D. Keep electric motors free of dirt and moisture
E. Maintain proper lubrication and oil levels
Explanation
The operator is expected to perform routine maintenance functions in order to prevent any issues in the sedimentation process. This includes checking the bearings for wear, overheating, and proper lubrication to ensure smooth operation. Good ventilation is necessary to maintain proper air circulation in the equipment work areas. Inspecting the alignment of shafts and couplings is important to prevent any misalignment that may cause damage. Keeping electric motors free of dirt and moisture ensures their efficient functioning. Finally, maintaining proper lubrication and oil levels is crucial for the overall performance of the equipment.

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• 35.

### What is the theoretical detention time for a rectangular sedimentation basin that is 80 feet long, 20 feet wide, 10 feet deep, and treats a flow of 2.0 MGD?

• A.

1.4 hours

• B.

1.6 hours

• C.

1.8 hours

• D.

2.0 hours

• E.

2.2 hours

A. 1.4 hours
Explanation
The theoretical detention time can be calculated by dividing the volume of the sedimentation basin by the flow rate. The volume of the basin can be found by multiplying the length, width, and depth. In this case, the volume is 80 ft x 20 ft x 10 ft = 16,000 cubic feet. The flow rate is given as 2.0 MGD, which stands for million gallons per day. To convert this to cubic feet per hour, we divide by 24 (to convert from days to hours) and multiply by 7.48 (to convert from gallons to cubic feet). So, the flow rate is 2.0 MGD / 24 hours * 7.48 cubic feet/gallon = 1.24 cubic feet/hour. Finally, we can calculate the detention time by dividing the volume by the flow rate: 16,000 cubic feet / 1.24 cubic feet/hour = 12,903.23 hours. Rounding to the nearest tenth gives us 1.4 hours.

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• 36.

### A tank with a capacity of 20,000 cubic feet can hold how many gallons of water?

• A.

112,200 gallons

• B.

123,400 gallons

• C.

134,640 gallons

• D.

149,600 gallons

• E.

179,500 gallons

D. 149,600 gallons
Explanation
To convert cubic feet to gallons, we need to know the conversion factor. One cubic foot is equal to 7.48 gallons. Therefore, the tank with a capacity of 20,000 cubic feet can hold 20,000 * 7.48 = 149,600 gallons of water.

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• 37.

### A tank with a capacity of 90 cubic feet can hold how many pounds of water?

• A.

3,120 pounds

• B.

3,780 pounds

• C.

4,368 pounds

• D.

4,992 pounds

• E.

5,616 pounds

E. 5,616 pounds
Explanation
The weight of water can be calculated by multiplying its volume by its density. The density of water is approximately 62.4 pounds per cubic foot. Therefore, the weight of 90 cubic feet of water would be 90 * 62.4 = 5,616 pounds.

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• 38.

### If a tank holds 300 pounds of water how many gallons of water are in the tank?

• A.

25.2 gallons

• B.

28.8 gallons

• C.

31.2 gallons

• D.

35.9 gallons

• E.

40.0 gallons

D. 35.9 gallons
Explanation
The correct answer is 35.9 gallons. To find the number of gallons, we need to convert the weight of water in pounds to gallons. Since 1 gallon of water weighs approximately 8.34 pounds, we can divide the weight of water in pounds (300) by the weight of 1 gallon (8.34) to get the number of gallons. 300 divided by 8.34 equals 35.9, which means there are 35.9 gallons of water in the tank.

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• 39.

### What is the surface area of a circular clarifier 35 feet in diameter?

• A.

962 square feet

• B.

1,256 square feet

• C.

1,480 square feet

• D.

1,590 square feet

• E.

1,960 square feet

A. 962 square feet
Explanation
The surface area of a circular clarifier can be calculated using the formula for the area of a circle, which is πr^2. In this case, the diameter of the clarifier is given as 35 feet, so the radius (r) would be half of that, which is 17.5 feet. Plugging this value into the formula, we get π(17.5)^2, which is approximately equal to 962 square feet.

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• 40.

### How many pounds of copper sulfate will be needed to dose a reservoir with 0.5 mg/L copper? The reservoir volume is 28 million gallons. The copper sulfate is 25 percent copper.

• A.

335 pounds

• B.

360 pounds

• C.

400 pounds

• D.

435 pounds

• E.

470 pounds

E. 470 pounds
Explanation
To calculate the amount of copper sulfate needed, we need to determine the amount of copper required for a reservoir volume of 28 million gallons. Since the desired concentration is 0.5 mg/L, we multiply it by the volume to find the total amount of copper needed. Next, since copper sulfate is 25% copper, we divide the total copper needed by 0.25 to find the total amount of copper sulfate needed. Therefore, the correct answer is 470 pounds.

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• Dec 30, 2011
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