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NJ Water/Wastewater Operator practice questions

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Question 1Source Water, Water Quality and Public Health Protection

What is the primary purpose of a maximum contaminant level (MCL) in public drinking water?

  1. To establish the minimum sampling frequency for each contaminant
  2. To cap a contaminant's concentration in delivered water Correct answer.
  3. To specify the treatment technology a system must install
  4. To define the deadline for reporting each contaminant result

Explanation

An MCL is a legal ceiling on the concentration of a regulated contaminant in water delivered to consumers. It is a health-based limit and does not prescribe the treatment method, sampling schedule, or reporting deadline.

Question 2Source Water, Water Quality and Public Health Protection

Turbidity in drinking water treatment is normally reported in which unit?

  1. Milligrams per liter
  2. Microsiemens per centimeter
  3. Standard pH units
  4. Nephelometric turbidity units Correct answer.

Explanation

Turbidity is measured by the amount of light scattered by suspended particles and is reported in nephelometric turbidity units (NTU). Milligrams per liter, microsiemens per centimeter, and pH units describe other water characteristics.

Question 3Source Water, Water Quality and Public Health Protection

Why does a distribution system maintain a disinfectant residual?

  1. To reduce hardness in the distribution system
  2. To remove dissolved iron from mains
  3. To raise the pH of stored water
  4. To protect against microbial regrowth Correct answer.

Explanation

A disinfectant residual provides continued protection against microbial regrowth and contamination within the distribution system after treatment. It is not intended to adjust pH, remove iron, or soften water.

Question 4Source Water, Water Quality and Public Health Protection

In the Total Coliform Rule, total coliform bacteria primarily serve as what?

  1. A direct measure of virus inactivation
  2. An indicator of nitrate contamination
  3. An indicator of distribution system contamination Correct answer.
  4. A test for corrosion control effectiveness

Explanation

Total coliforms are used as indicator organisms because their presence suggests a pathway for contamination or a loss of distribution system integrity. They do not directly measure viruses, nitrate, or corrosion control performance.

Question 5Source Water, Water Quality and Public Health Protection

The federal MCL for nitrate is set mainly to protect against which condition?

  1. Kidney damage in adults
  2. Thyroid dysfunction in adults
  3. Methemoglobinemia in infants Correct answer.
  4. Dental fluorosis in children

Explanation

High nitrate levels can cause methemoglobinemia, often called blue baby syndrome, in infants. Dental fluorosis is associated with fluoride, while the other listed effects are not the basis for the nitrate MCL.

Question 6Source Water, Water Quality and Public Health Protection

A watershed is best described as what?

  1. The treatment plant's finished water storage area
  2. The land area that drains to a given water body Correct answer.
  3. The zone where wells are sealed with grout
  4. The portion of a distribution system beyond the plant

Explanation

A watershed is the land area from which water drains into a particular stream, lake, or other water body. Storage areas and distribution piping are infrastructure, while grouting zones relate to well construction.

Question 7Source Water, Water Quality and Public Health Protection

A source water assessment program mainly does what?

  1. Identifies potential threats to a drinking water source Correct answer.
  2. Sets the MCL for each regulated contaminant
  3. Certifies laboratory analysts for drinking water testing
  4. Calculates the CT value needed for disinfection

Explanation

A source water assessment evaluates the area around a drinking water source to identify potential contamination sources and the source's susceptibility. It does not set MCLs, certify analysts, or calculate disinfection CT values.

Question 8Source Water, Water Quality and Public Health Protection

Which characteristic makes Cryptosporidium difficult to control with chlorine alone?

  1. It is measured by turbidity
  2. It is easily filtered from raw water
  3. Its oocysts resist common chlorine doses Correct answer.
  4. It grows only in distribution mains

Explanation

Cryptosporidium forms oocysts that are highly resistant to commonly used free chlorine residuals. Treatment therefore relies on physical removal and other disinfectants, such as ultraviolet light or ozone.

Question 9Source Water, Water Quality and Public Health Protection

Under the Surface Water Treatment Rule, a conventional filtered system must keep combined filter effluent turbidity at or below what level in at least 95% of monthly measurements?

  1. 10.0 NTU
  2. 5.0 NTU
  3. 0.3 NTU Correct answer.
  4. 1.0 NTU

Explanation

Conventional filtration systems must meet a combined filter effluent limit of 0.3 NTU in at least 95% of monthly measurements, with no individual reading above 1 NTU. The other values are far above the regulatory turbidity limit.

Question 10Source Water, Water Quality and Public Health Protection

In disinfection, the CT value is calculated by multiplying disinfectant concentration by what?

  1. The contact time Correct answer.
  2. The turbidity
  3. The water temperature
  4. The pH

Explanation

CT stands for concentration times time, so the disinfectant residual concentration is multiplied by the effective contact time. Temperature and pH affect disinfection efficiency, but they are not multiplied in the basic CT calculation.

Question 11Source Water, Water Quality and Public Health Protection

The Stage 2 Disinfectants and Disinfection Byproducts Rule sets a locational running annual average limit of 80 µg/L for which group?

  1. Nitrate
  2. Total trihalomethanes Correct answer.
  3. Haloacetic acids
  4. Arsenic

Explanation

The Stage 2 DBPR limit is 80 µg/L for total trihalomethanes and 60 µg/L for five haloacetic acids, both as locational running annual averages. Nitrate and arsenic are regulated under separate contaminant standards.

Question 12Source Water, Water Quality and Public Health Protection

A community water system exceeds the lead action level. What is the required response?

  1. Switch to bottled water for all users
  2. Install granular activated carbon at every tap
  3. Issue a boil water notice immediately
  4. Optimize corrosion control treatment Correct answer.

Explanation

An action level exceedance triggers corrosion control optimization and related public education requirements. Boil water notices and system-wide bottled water are not the standard response to a lead action level exceedance.

Question 13Source Water, Water Quality and Public Health Protection

The federal MCL for arsenic in drinking water is what?

  1. 10 µg/L Correct answer.
  2. 50 µg/L
  3. 5 µg/L
  4. 100 µg/L

Explanation

The current federal arsenic MCL is 10 µg/L. The older standard of 50 µg/L was lowered, and 5 µg/L and 100 µg/L are not the federal MCL.

Question 14Source Water, Water Quality and Public Health Protection

The federal MCL for nitrate, expressed as nitrogen, is what?

  1. 50 mg/L
  2. 100 mg/L
  3. 1 mg/L
  4. 10 mg/L Correct answer.

Explanation

The nitrate MCL is 10 mg/L when expressed as nitrogen. Nitrate is sometimes reported as nitrate ion, which uses a different numerical value, so the as-nitrogen basis must be noted.

Question 15Source Water, Water Quality and Public Health Protection

A wellhead protection area is generally defined by what?

  1. The property line of the well owner
  2. The area feeding a well within a set travel time Correct answer.
  3. The fenced boundary of the treatment plant
  4. The full service area of the distribution system

Explanation

Wellhead protection areas are commonly based on groundwater travel time to the well, such as a one-year time-of-travel zone. Property lines, service areas, and plant fences do not define the contributing area.

Question 16Source Water, Water Quality and Public Health Protection

A sanitary survey of a public water system is conducted to do what?

  1. Measure the chlorine demand of the untreated raw water
  2. Review facilities, operations, and source protection Correct answer.
  3. Determine the finished water's hardness
  4. Establish the system's water rates

Explanation

A sanitary survey is a comprehensive review of the system's facilities, operations, monitoring, and source protection to identify deficiencies. It is not a water quality test for chlorine demand or hardness, nor a rate-setting process.

Question 17Source Water, Water Quality and Public Health Protection

Why is raw source water monitored separately from finished water?

  1. To satisfy distribution system residual rules
  2. To measure customer tap lead levels
  3. To track incoming quality and adjust treatment Correct answer.
  4. To set the system's water rates

Explanation

Raw water monitoring shows the quality of water entering the plant so operators can adjust treatment to meet finished water standards. Distribution residual rules and tap lead monitoring apply to other parts of the system.

Question 18Source Water, Water Quality and Public Health Protection

Which treatment is most effective for inactivating Cryptosporidium oocysts?

  1. Aeration alone
  2. Ultraviolet light disinfection Correct answer.
  3. Chloramine at normal residual
  4. Free chlorine at normal residual

Explanation

Ultraviolet light is effective against Cryptosporidium oocysts at relatively low doses. Free chlorine and chloramine residuals at normal levels do not reliably inactivate the oocysts, and aeration does not disinfect.

Question 19Source Water, Water Quality and Public Health Protection

Which source water characteristic most increases formation of trihalomethanes during chlorination?

  1. High calcium hardness
  2. High dissolved oxygen
  3. High alkalinity
  4. High natural organic matter Correct answer.

Explanation

Natural organic matter reacts with chlorine to form trihalomethanes and other disinfection byproducts. Alkalinity, dissolved oxygen, and calcium hardness are not the primary precursors for trihalomethane formation.

Question 20Source Water, Water Quality and Public Health Protection

Under the Stage 2 DBPR, compliance with TTHM and HAA5 limits is based on what?

  1. The highest monthly sample in the system
  2. A site-specific running annual average Correct answer.
  3. A single sample at the plant tap
  4. The average of all raw water samples

Explanation

Stage 2 DBPR compliance is based on a locational running annual average at each monitoring site, which accounts for persistent elevated results at individual locations. Single samples and raw water averages do not determine compliance.

Question 21Source Water, Water Quality and Public Health Protection

The Long Term 2 Enhanced Surface Water Treatment Rule requires systems to do what?

  1. Test every service connection for lead each year
  2. Maintain a minimum chlorine residual of 2 mg/L
  3. Sample every storage tank for nitrate each month
  4. Monitor for Cryptosporidium and treat as needed Correct answer.

Explanation

The LT2ESWTR requires source water monitoring for Cryptosporidium and assigns additional treatment based on the monitoring results. Lead tap testing, a fixed 2 mg/L residual, and monthly tank nitrate sampling are not LT2 requirements.

Question 22Source Water, Water Quality and Public Health Protection

The Ground Water Rule requires a groundwater system with a significant deficiency to do what?

  1. Switch to a surface water source
  2. Install granular activated carbon for nitrate
  3. Sample for radon at every entry point daily
  4. Provide at least 4-log virus treatment Correct answer.

Explanation

The Ground Water Rule requires corrective action for significant deficiencies, including providing at least 4-log virus treatment or an equivalent state-approved approach. Switching sources, carbon for nitrate, and daily radon sampling are not the rule's standard requirement.

Question 23Source Water, Water Quality and Public Health Protection

Under the Surface Water Treatment Rule, a filtered system must achieve at least what overall removal/inactivation of Giardia lamblia?

  1. 99.99 percent (4-log)
  2. 99 percent (2-log)
  3. 90 percent (1-log)
  4. 99.9 percent (3-log) Correct answer.

Explanation

The SWTR requires at least 99.9 percent (3-log) removal and/or inactivation of Giardia lamblia and 99.99 percent (4-log) for viruses. The 4-log value applies to viruses, not Giardia.

Question 24Source Water, Water Quality and Public Health Protection

Why is turbidity used as a key indicator in filtered surface water systems?

  1. It measures the water's calcium content
  2. It directly measures virus concentration
  3. It indicates the chlorine dose required by rule
  4. It shows particle and pathogen removal effectiveness Correct answer.

Explanation

Turbidity is a surrogate for particulate removal; low filtered water turbidity suggests that particles, including pathogens, are being removed effectively. It does not directly measure viruses, set chlorine dose, or measure calcium.

Question 25Source Water, Water Quality and Public Health Protection

In wellhead protection, a one-year time-of-travel boundary is used to do what?

  1. Establish the chlorine residual at the wellhead
  2. Determine the well's required casing depth
  3. Define the area likely to affect the well quickly Correct answer.
  4. Set the maximum pumping rate of the well

Explanation

A one-year time-of-travel boundary identifies the area from which groundwater can reach the well within one year, helping focus protection efforts on the most immediate threats. It does not set pumping rates, chlorine residual, or casing depth.

Question 26Source Water, Water Quality and Public Health Protection

What is the federal primary maximum contaminant level (MCL) for fluoride in drinking water?

  1. 8.0 mg/L
  2. 2.0 mg/L
  3. 4.0 mg/L Correct answer.
  4. 10 mg/L

Explanation

The primary MCL for fluoride is 4.0 mg/L, set to protect against crippling skeletal fluorosis. A separate secondary standard of 2.0 mg/L addresses the aesthetic problem of dental fluorosis (mottling of teeth) in children.

Question 27Source Water, Water Quality and Public Health Protection

Hardness in a drinking water supply is caused primarily by the presence of which two ions?

  1. Chloride and sulfate
  2. Calcium and magnesium Correct answer.
  3. Iron and manganese
  4. Sodium and potassium

Explanation

Hardness is defined as the sum of divalent metal ions, predominantly calcium and magnesium, and is usually reported as mg/L calcium carbonate. Iron and manganese are separate secondary-standard concerns that can add minor hardness but are not the primary cause.

Question 28Source Water, Water Quality and Public Health Protection

A routine sample from a distribution system tests positive for total coliform bacteria. What does this result primarily indicate?

  1. The supply is free of pathogenic organisms
  2. A barrier may have failed, allowing contamination Correct answer.
  3. The chlorine residual is too low to measure
  4. Fecal contamination is definitely present in the water

Explanation

Total coliforms are indicator organisms: their presence signals that a treatment barrier or distribution integrity problem may have allowed contamination to enter, or that regrowth is occurring. The test does not by itself confirm fecal contamination or identify a specific pathogen.

Question 29Source Water, Water Quality and Public Health Protection

A shallow, unconfined sand-and-gravel aquifer lies beneath farmland with permeable soils. Which characteristic most increases this aquifer's vulnerability to nitrate contamination?

  1. A thick clay layer above the water table
  2. Long groundwater travel times to the well
  3. High natural pH of the aquifer material
  4. Rapid recharge through permeable soils Correct answer.

Explanation

Vulnerability of an unconfined aquifer depends largely on how quickly contaminants can move from the land surface to the water table. Permeable soils with rapid recharge and little overlying clay allow nitrate from fertilizer or septic systems to reach the well with minimal attenuation.

Question 30Source Water, Water Quality and Public Health Protection

A utility replaces a direct river intake with wells screened in the aquifer beside the river (riverbank filtration). What is the primary water quality benefit of this change?

  1. It guarantees compliance with all MCLs
  2. It removes the need for any disinfection
  3. It raises the river stage near the intake
  4. Soil passage filters particles and reduces pathogens Correct answer.

Explanation

As river water moves through bank sediments, physical filtration, sorption, and biodegradation reduce turbidity, pathogens, and organic matter, producing a more stable and higher-quality raw water. Treatment and disinfection are still required because the improvement is a matter of degree, not a guarantee.

Question 31Source Water, Water Quality and Public Health Protection

Which set of source water conditions is most likely to promote a cyanotoxin problem?

  1. Warm, slow-moving, nutrient-rich water Correct answer.
  2. Cold, fast-moving water that is low in nutrients
  3. Deep confined groundwater with very low oxygen
  4. Turbid water following a winter storm event

Explanation

Cyanobacteria thrive in warm, slow-moving or stagnant water enriched with nutrients such as phosphorus and nitrogen, conditions that produce dense blooms capable of releasing toxins. Utilities monitor for blooms and may add treatment steps such as activated carbon or oxidation.

Question 32Source Water, Water Quality and Public Health Protection

For free chlorine disinfection at typical water temperatures, which regulated microbial group generally governs the required CT because it is the most resistant to chlorine?

  1. Giardia lamblia cysts Correct answer.
  2. Total coliform bacteria
  3. Heterotrophic bacteria
  4. Enteric viruses

Explanation

Protozoan cysts are far more resistant to free chlorine than vegetative bacteria or enteric viruses, so CT tables for chlorination are typically driven by Giardia. Cryptosporidium oocysts are more resistant still, but chlorine is not credited for their inactivation.

Question 33Source Water, Water Quality and Public Health Protection

Chloride and sodium concentrations in a coastal supply well rise steadily over several years while other water quality parameters remain stable. What is the most likely cause?

  1. Leakage of connate water through the casing seal
  2. Saltwater intrusion from pumping drawdown Correct answer.
  3. Corrosion of the well casing releasing sodium
  4. Chlorination at the wellhead raising chloride

Explanation

Sustained pumping lowers the freshwater head and can allow saline water to migrate toward the well, producing gradual increases in sodium and chloride. A steady multi-year trend in both ions is the classic signature of intrusion rather than a sudden mechanical or treatment-related change.

Question 34Source Water, Water Quality and Public Health Protection

After a heavy rain, a river-fed plant's raw water turbidity rises sharply and the chlorine dose needed to hold residual climbs, although filtered water turbidity remains within limits. Which interpretation best fits these observations?

  1. Runoff is adding turbidity and chlorine-consuming organics Correct answer.
  2. The chlorine feed pump has lost its calibration
  3. The filters have failed and must be taken offline immediately
  4. The filter effluent has exceeded its turbidity limit

Explanation

Storm runoff carries soil particles and natural organic matter into the source water; the particles raise raw turbidity and the organics exert chlorine demand, so more chlorine is needed to maintain residual. Because filtered turbidity is still in compliance, the treatment barriers are working, but the utility should intensify source water monitoring and adjust coagulant dose.

Question 35Treatment Processes and Process Control

In an activated sludge system, the mixed liquor suspended solids (MLSS) concentration represents which of the following?

  1. The concentration of solids in the sludge drawn off the final clarifier
  2. The concentration of solids in the aeration tank contents Correct answer.
  3. The concentration of solids leaving the plant in the final effluent
  4. The concentration of solids in the primary effluent entering the plant

Explanation

Mixed liquor is the combination of influent wastewater and the biological sludge in the aeration tank, so MLSS measures the total suspended solids in that tank. It is the biomass inventory used with the BOD load to set F/M and sludge age. Effluent and primary samples are measured separately and are not mixed liquor.

Question 36Treatment Processes and Process Control

Which of the following best describes the main purpose of a primary clarifier in a wastewater treatment plant?

  1. To dewater waste activated sludge into a cake suitable for landfill disposal
  2. To convert ammonia to nitrate using nitrifying bacteria on attached growth media
  3. To settle settleable solids and reduce the organic load on later processes Correct answer.
  4. To disinfect the raw wastewater with chlorine before it reaches the aeration tank

Explanation

Primary clarification is a physical settling step that removes settleable solids, grit-associated material, and a portion of the BOD before biological treatment. Reducing this load lowers aeration demand and sludge production downstream. Disinfection, nitrification, and dewatering are separate processes located elsewhere in the plant.

Question 37Treatment Processes and Process Control

Chlorine demand is best described as which of the following?

  1. The amount of chlorine that remains after the contact period
  2. The chlorine dose needed to reach a target CT value
  3. The amount of chlorine consumed by substances in the water during contact Correct answer.
  4. The concentration of chloramine formed when ammonia is present

Explanation

Chlorine demand is the difference between the dose applied and the residual left, meaning the chlorine taken up by reducing agents, organics, ammonia, and other oxidizable material. Residual is what remains after demand is satisfied. CT values and chloramine concentrations are related concepts but are not the definition of demand.

Question 38Treatment Processes and Process Control

Which of the following is the purpose of backwashing a granular media filter?

  1. To increase the filtration rate by re-grading the media
  2. To add coagulant to the media bed for the next filter run
  3. To disinfect the media with a concentrated chlorine solution
  4. To flush accumulated solids out of the media bed Correct answer.

Explanation

Backwashing reverses flow through the bed at a rate high enough to expand and scrub the media, carrying captured particles to waste. It restores the porosity and head loss capacity lost during the filter run. Coagulant is added ahead of the filter, not during backwash.

Question 39Treatment Processes and Process Control

The sludge volume index (SVI) of an activated sludge sample is determined to assess which property?

  1. How well the sludge settles and compacts Correct answer.
  2. How much oxygen the sludge consumes per hour
  3. How completely the sludge can be dewatered on a belt press
  4. How rapidly the sludge digests under anaerobic conditions

Explanation

SVI is the volume occupied by one gram of settled solids after a standard settling test, so it is an indicator of sludge settleability and compaction. A low SVI indicates dense, well-settling sludge, while a high SVI suggests filamentous bulking or poor floc structure. Oxygen uptake and dewaterability are measured by other tests.

Question 40Treatment Processes and Process Control

Nitrifying bacteria in an aeration tank require which of the following to convert ammonia to nitrate?

  1. Ferric chloride and a polymer
  2. Dissolved oxygen and alkalinity Correct answer.
  3. An anaerobic environment with no dissolved oxygen
  4. A high organic loading and a short sludge age

Explanation

Nitrification is an aerobic process, so the nitrifiers need dissolved oxygen, and the reaction consumes alkalinity, which can depress pH if it is not adequate. Because nitrifiers grow slowly, they also need a sufficiently long sludge age and low organic loading to persist. Chemical coagulants play no role in the conversion.

Question 41Treatment Processes and Process Control

The gas produced in greatest quantity by a properly operating anaerobic digester is which of the following?

  1. Ammonia
  2. Carbon dioxide
  3. Hydrogen sulfide
  4. Methane Correct answer.

Explanation

Digester gas is typically about 60 to 70 percent methane, with carbon dioxide making up most of the remainder. Methane is the valuable component because it carries the heating value used for boilers and engines. Hydrogen sulfide and ammonia are present only in small amounts.

Question 42Treatment Processes and Process Control

A jar test is performed to determine which of the following?

  1. The solids loading rate on the filter
  2. The best coagulant dose for the water Correct answer.
  3. The chlorine demand of the finished water
  4. The sludge age of the activated sludge process

Explanation

A jar test stirs several identical samples at increasing coagulant doses and compares floc formation and settled turbidity. The dose that produces the best floc and clearest supernatant is selected for the plant. It does not measure chlorine demand, filter loading, or sludge age.

Question 43Treatment Processes and Process Control

In an activated sludge plant, if the F/M ratio is increased while all other conditions stay the same, which of the following is the most likely result?

  1. More food per unit of biomass, which tends to raise the sludge age
  2. More food per unit of biomass, which tends to reduce the sludge age Correct answer.
  3. No change in sludge age because biomass and food change together
  4. Less food per unit of biomass, which tends to reduce the sludge age

Explanation

F/M is the BOD or COD load divided by the biomass inventory, so a higher F/M means more food available per unit of organisms. With more food per organism, the population grows faster and the solids inventory is turned over more quickly, which corresponds to a lower sludge age. F/M and MCRT move in opposite directions.

Question 44Treatment Processes and Process Control

A plant's MCRT is 18 days and the target is 10 days. Which action would move the MCRT toward the target?

  1. Increase the waste activated sludge flow Correct answer.
  2. Increase the return activated sludge flow
  3. Decrease the waste activated sludge flow
  4. Reduce aeration so the mixed liquor solids drop

Explanation

MCRT is the mass of solids held in the aeration system divided by the mass of solids leaving each day. Wasting more sludge increases the daily solids removed, so the calculated sludge age falls toward the target. Return sludge rate affects solids distribution between the tank and clarifier but not the total mass wasted.

Question 45Treatment Processes and Process Control

An anoxic zone is placed ahead of the aeration tank in a biological nutrient removal plant primarily to accomplish which of the following?

  1. To precipitate phosphorus with ferric chloride
  2. To remove grit and other heavy inert material
  3. To oxidize ammonia to nitrate using added oxygen
  4. To convert nitrate to nitrogen gas using influent organic matter Correct answer.

Explanation

In the anoxic zone, denitrifying bacteria use nitrate recycled from the aerobic zone as an oxygen source while consuming influent carbon, releasing nitrogen gas. Keeping the zone free of dissolved oxygen forces the bacteria to use nitrate. Ammonia oxidation requires oxygen and occurs in the aerobic zone.

Question 46Treatment Processes and Process Control

The sludge blanket in a final clarifier is rising and beginning to carry over the weirs. Which of the following is the most appropriate first response?

  1. Reduce the return activated sludge rate to let the blanket settle
  2. Increase the return sludge rate to pull solids back Correct answer.
  3. Add polymer to the aeration tank to improve flocculation
  4. Increase wasting and reduce the aeration tank dissolved oxygen to zero

Explanation

A rising blanket means solids are being stored in the clarifier faster than they are being returned, so increasing the return sludge rate moves solids back to the aeration tank and lowers the blanket. If the blanket remains high, wasting or reducing solids inventory may also be needed. Cutting return flow or solids inventory prematurely can worsen the carryover.

Question 47Treatment Processes and Process Control

Dissolved oxygen in an aeration tank is normally controlled by adjusting which of the following?

  1. The lime feed to the digester
  2. The polymer feed to the belt press
  3. The air supplied by the blowers or aerators Correct answer.
  4. The ferric chloride feed rate

Explanation

Aeration tank dissolved oxygen responds to the balance between oxygen supplied and oxygen consumed by the biomass. Operators adjust blower output, valve position, or aerator speed to hold the DO setpoint, often in response to online DO readings. Chemical feed rates affect other parts of the plant and do not control DO.

Question 48Treatment Processes and Process Control

A plant reports an SVI of 250 mL/g with a cloudy effluent and a low F/M ratio. Which condition is most likely?

  1. A pin floc caused by an overdose of polymer
  2. Denitrification floating sludge in the clarifier
  3. Filamentous bulking from a low F/M and long sludge age Correct answer.
  4. A young sludge with rapid growth and poor flocculation

Explanation

Filamentous organisms often thrive at low F/M and long sludge age, and their filaments produce a loose, high-volume sludge that settles poorly, giving a high SVI and cloudy effluent. A young sludge or pin floc would typically show a low SVI with fine particles. Denitrification produces rising clumps of sludge, not a uniformly high SVI.

Question 49Treatment Processes and Process Control

At the breakpoint on a chlorine dose-residual curve, which of the following has occurred?

  1. All chlorine has been converted to chloramine and the residual is stable
  2. The water has become anaerobic and chlorine is no longer effective
  3. Chlorine demand has been met, so free residual rises Correct answer.
  4. The chlorine residual has reached its maximum possible value

Explanation

As chlorine is added, it first oxidizes reducing substances and ammonia, and combined residual rises then falls as chloramines are destroyed. At the breakpoint, demand is satisfied and further chlorine appears as free residual that increases with dose. This is why breakpoint chlorination is used to achieve a free chlorine residual.

Question 50Treatment Processes and Process Control

Organic loading on a trickling filter is expressed in which of the following units?

  1. lb BOD/day per 1,000 cu ft of media Correct answer.
  2. pounds of solids per day per linear foot
  3. gallons per day per square foot
  4. mg/L of mixed liquor suspended solids

Explanation

Trickling filter organic loading is the mass of BOD applied per day per unit volume of filter media, commonly pounds BOD per day per 1,000 cubic feet. Hydraulic loading, in gallons per day per square foot of surface area, is a separate parameter. Mixed liquor solids belong to suspended growth systems, not trickling filters.