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ME Water Operator practice questions

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Question 1Water treatment

A groundwater source contains dissolved iron and manganese in the reduced (ferrous/manganous) form. Which treatment sequence is standard for removing these metals?

  1. Coagulation followed by sedimentation
  2. Ion exchange softening followed by chlorination
  3. Oxidation followed by filtration Correct answer.
  4. Aeration followed by lime softening

Explanation

Reduced iron and manganese must first be oxidized to an insoluble form, then removed by filtration. Chlorine, potassium permanganate, or aeration serve as the oxidant, and the precipitated particles are captured in a filter bed.

Question 2Water treatment

What is the primary purpose of the flocculation step in a conventional surface water treatment plant?

  1. To strip dissolved gases from the water
  2. To provide gentle mixing that encourages small particles to collide and grow into larger floc Correct answer.
  3. To disinfect the water before sedimentation
  4. To increase the velocity gradient so particles settle by gravity

Explanation

Flocculation uses slow, gentle mixing to promote collisions between destabilized particles so they aggregate into settleable floc. Rapid mixing, by contrast, disperses the coagulant, and sedimentation removes the floc that forms.

Question 3Water treatment

A water sample has a pH of 7.0. What is the approximate hydrogen ion concentration?

  1. 1 × 10^7 moles per liter
  2. 7 moles per liter
  3. 1 × 10^-7 moles per liter Correct answer.
  4. 0.7 moles per liter

Explanation

pH is defined as the negative base-10 logarithm of hydrogen ion activity, so pH 7 corresponds to 1 × 10^-7 mol/L. Each unit change in pH reflects a tenfold change in hydrogen ion concentration.

Question 4Water treatment

Why is chlorine residual measured at the far end of the distribution system rather than only at the treatment plant exit?

  1. To confirm that disinfection capacity persists throughout the system and reaches distant customers Correct answer.
  2. To measure the total organic carbon concentration in the water
  3. To verify that the filter media is properly graded
  4. To determine the hardness of the finished water

Explanation

Residual disinfectant must be maintained throughout the distribution system to protect against contamination after treatment. Sampling at distant points confirms that chlorine demand and decay have not consumed the residual before it reaches customers.

Question 5Water treatment

A rapid sand filter is operating with a head loss that has reached its terminal limit, but the effluent turbidity remains acceptable. What is the appropriate operational response?

  1. Backwash the filter to restore the media bed Correct answer.
  2. Continue running until turbidity breakthrough occurs
  3. Add more coagulant to the filter influent
  4. Increase the filtration rate to push through the clogged media

Explanation

When terminal head loss is reached, the filter must be backwashed to remove accumulated solids and restore flow capacity. Waiting for turbidity breakthrough risks passing particles and is not an acceptable operating practice.

Question 6Water treatment

Which unit process is primarily responsible for removing dissolved gases such as carbon dioxide and volatile organic compounds from water?

  1. Filtration
  2. Sedimentation
  3. Fluoridation
  4. Aeration Correct answer.

Explanation

Aeration brings water into contact with air so dissolved gases can transfer from the liquid phase to the atmosphere. It is also used to oxidize iron and to strip volatile organics and carbon dioxide.

Question 7Water treatment

What does a turbidity measurement in finished water primarily indicate?

  1. The alkalinity of the water
  2. The corrosivity of the water toward pipe materials
  3. The presence of suspended particles that can shield microorganisms from disinfection Correct answer.
  4. The concentration of dissolved minerals

Explanation

Turbidity measures light scattering by suspended particles, which can harbor pathogens and interfere with disinfection. Low finished-water turbidity is therefore a key indicator of treatment effectiveness and microbial safety.

Question 8Water treatment

A water treatment plant uses a coagulant that consumes alkalinity, and finished water pH has dropped below the target. Which corrective action is most appropriate?

  1. Reduce the filter backwash frequency
  2. Increase the coagulant dose to stabilize pH
  3. Add a base such as lime or caustic soda to raise pH and restore alkalinity Correct answer.
  4. Add chlorine to raise the pH

Explanation

Coagulants such as alum consume natural alkalinity and depress pH, so adding an alkaline chemical restores both pH and buffering capacity. Lime, hydrated lime, or caustic soda are commonly used for this purpose.

Question 9Water treatment

In a softening plant, a jar test is used to determine which parameter before full-scale operation?

  1. The optimum chemical dose for the treatment goal Correct answer.
  2. The chlorine decay coefficient
  3. The distribution system pressure
  4. The filter media size distribution

Explanation

Jar tests simulate coagulation, softening, or other chemical treatment on a small scale to identify the optimum chemical dose and mixing conditions. The results guide full-scale dosing to achieve the target water quality.

Question 10Water treatment

A filter run shows turbidity breakthrough shortly after backwash even though head loss is low. Which condition is the most likely cause?

  1. Media loss or disturbance creating a preferential flow path Correct answer.
  2. High coagulant dose in the raw water
  3. Excessive filter run length
  4. Low raw water turbidity

Explanation

Early breakthrough with low head loss suggests short-circuiting, often caused by media loss, media upset, or a disturbed bed after backwash. The filter must be inspected and the media restored or restratified.

Question 11Water treatment

Why is it important to maintain a minimum chlorine residual in the distribution system rather than only achieving a high dose at the plant?

  1. Because the residual provides ongoing protection against contamination and regrowth throughout the system Correct answer.
  2. Because a high plant dose guarantees disinfection at all points
  3. Because residual chlorine increases water hardness
  4. Because residual chlorine removes dissolved iron

Explanation

A maintained residual continues to inactivate microorganisms and provides a barrier against contamination that may enter the distribution system. Monitoring at representative points confirms that protection persists to the farthest customers.

Question 12Water treatment

A plant reports that finished water turbidity is consistently below the regulatory limit, but individual filter effluent turbidity spikes briefly after each backwash. What is the best interpretation?

  1. The backwash rate should be increased to maximum
  2. The coagulant dose should be eliminated
  3. The filters are performing well and no action is needed
  4. Filter-to-waste or a filter ripening period should be used to manage post-backwash spikes Correct answer.

Explanation

Post-backwash turbidity spikes are a normal ripening phenomenon and can be managed by filtering to waste until effluent quality stabilizes. This prevents the spike from reaching the finished water.

Question 13Water treatment

Which disinfectant is typically chosen when a long-lasting residual is needed in a large distribution system?

  1. Chloramines Correct answer.
  2. Ultraviolet light
  3. Ozone
  4. Chlorine dioxide

Explanation

Chloramines are more stable than free chlorine and persist longer in distribution systems, making them useful where a durable residual is required. They are formed by combining chlorine with ammonia.

Question 14Water treatment

A water system uses alum coagulation. What is the primary mechanism by which alum destabilizes particles?

  1. It raises the pH to precipitate calcium carbonate
  2. It neutralizes negative surface charges on particles and enmeshes them in a hydroxide precipitate Correct answer.
  3. It increases the dissolved oxygen concentration
  4. It adds chlorine to oxidize organic matter

Explanation

Alum hydrolyzes to form positively charged species that neutralize the negative charges on particles, and the resulting aluminum hydroxide precipitate enmeshes particles. This allows the particles to aggregate into settleable floc.

Question 15Water treatment

Which parameter is most directly used to determine the lime dose required for softening water with high calcium hardness?

  1. The total alkalinity and calcium hardness concentrations Correct answer.
  2. The fluoride concentration
  3. The chlorine demand of the water
  4. The turbidity of the finished water

Explanation

Lime softening removes calcium hardness by precipitating calcium carbonate, and the required dose depends on the calcium hardness and alkalinity present. These concentrations are measured to calculate the stoichiometric lime requirement.

Question 16Water treatment

A treatment plant operator observes that filter backwash water is unusually muddy and the bed appears to have lost depth. What is the most likely cause?

  1. Low filter loading rate
  2. Excessive backwash rate causing media expansion and loss Correct answer.
  3. High raw water pH
  4. Insufficient coagulant addition

Explanation

Backwash rates that are too high expand the bed excessively and can wash media over the wash troughs, reducing bed depth. This leads to poor filtration and requires rate adjustment and media replacement.

Question 17Water treatment

Which of the following best describes the purpose of a clearwell in a surface water treatment plant?

  1. To provide contact time for disinfection and to store finished water Correct answer.
  2. To dewater filter backwash sludge
  3. To remove dissolved iron and manganese
  4. To flocculate particles before sedimentation

Explanation

A clearwell provides detention time for disinfectant contact and stores treated water to balance plant production against demand. It is typically located after filtration and disinfection.

Question 18Water treatment

A water sample is measured to have a pH of 6.5 and a total alkalinity of 20 mg/L as CaCO3. What treatment concern does this combination most likely raise?

  1. The water has excessive fluoride
  2. The water is likely to be corrosive and poorly buffered Correct answer.
  3. The water contains excessive dissolved oxygen
  4. The water is likely to form heavy scale deposits

Explanation

Low pH combined with low alkalinity means the water has little buffering capacity and tends to be corrosive to metal piping. Adjusting pH and alkalinity is typically required to stabilize the water.

Question 19Water treatment

What is the primary function of the sedimentation basin following coagulation and flocculation?

  1. To adjust the fluoride concentration
  2. To oxidize dissolved iron
  3. To allow floc to settle out by gravity before filtration Correct answer.
  4. To disinfect the water with chlorine

Explanation

Sedimentation provides quiescent conditions and detention time for floc to settle by gravity, reducing the solids load on filters. Removing floc before filtration extends filter runs and improves effluent quality.

Question 20Water treatment

An operator notes that the chlorine dose at the plant is 3.0 mg/L and the residual leaving the plant is 1.2 mg/L. What does the difference primarily represent?

  1. The turbidity of the water
  2. The alkalinity of the water
  3. The chlorine demand of the water Correct answer.
  4. The hardness of the water

Explanation

Chlorine demand is the difference between the applied dose and the residual remaining after contact, representing chlorine consumed by oxidizable substances. The 1.8 mg/L difference in this example is the demand exerted.

Question 21Water treatment

A surface water source with high color and low turbidity is difficult to coagulate. Which approach is most commonly used to improve treatment?

  1. Adjust pH and coagulant dose, possibly adding a coagulant aid, to optimize removal of color-causing organics Correct answer.
  2. Discontinue sedimentation and filter directly
  3. Reduce coagulant dose and rely on filtration alone
  4. Increase filter loading rate to improve color removal

Explanation

Low-turbidity, high-color waters often require pH adjustment and careful coagulant dosing to precipitate dissolved organics effectively. A coagulant aid or polymer can strengthen floc and improve removal.

Question 22Water treatment

Which statement correctly describes the relationship between alkalinity and pH stability during coagulation with a metal salt coagulant?

  1. Alkalinity has no effect on pH during coagulation
  2. Adequate alkalinity buffers the water and prevents excessive pH depression when coagulant is added Correct answer.
  3. Higher alkalinity always increases coagulant demand without affecting pH
  4. Alkalinity must be zero for coagulation to occur

Explanation

Alkalinity provides buffering capacity that resists pH changes as coagulant consumes alkalinity. When alkalinity is insufficient, pH can drop sharply and impair coagulation, requiring alkaline chemical addition.

Question 23Water treatment

A plant treats water with a high concentration of natural organic matter. Which treatment change best reduces the formation of disinfection byproducts during chlorination?

  1. Reducing backwash frequency
  2. Increasing chlorine dose before filtration
  3. Switching to a higher filter loading rate
  4. Removing organic precursors through enhanced coagulation and adjusting the point of chlorination Correct answer.

Explanation

Disinfection byproducts form when chlorine reacts with natural organic matter, so reducing precursor concentrations through enhanced coagulation lowers formation potential. Adjusting the chlorination point and dose further limits the reaction.

Question 24Water treatment

A distribution system experiences complaints of red water at customer taps. Which condition is the most likely explanation?

  1. Corrosion or disturbance of iron pipe scales releasing iron particles into the water Correct answer.
  2. Low turbidity in the finished water
  3. High chlorine residual throughout the system
  4. Excessive fluoride in the finished water

Explanation

Red water typically results from iron corrosion products or iron-bearing scales being released into the water, often after hydraulic disturbances or changes in water chemistry. Controlling corrosion and stabilizing water quality prevent the release.

Question 25Water treatment

An operator must evaluate whether a filter is performing adequately after a media replacement. Which combination of observations provides the strongest evidence of proper performance?

  1. Effluent turbidity equal to raw water turbidity
  2. Rapid turbidity breakthrough after each backwash
  3. Stable low effluent turbidity and a normal head loss development pattern over the run Correct answer.
  4. High initial head loss and frequent backwashing

Explanation

A properly functioning filter produces consistently low effluent turbidity while head loss increases gradually over the filter run. Both indicators together confirm that particles are being captured rather than passing through.

Question 26Water treatment

Which chemical is most commonly added to water to raise pH and alkalinity without adding hardness in a surface water treatment plant?

  1. Aluminum sulfate
  2. Sodium hydroxide Correct answer.
  3. Sodium chloride
  4. Calcium oxide

Explanation

Sodium hydroxide raises pH and adds alkalinity as the hydroxide ion without introducing calcium or magnesium hardness. Quicklime (calcium oxide) raises pH but adds calcium hardness and requires careful slaking. Alum is an acidic coagulant that consumes alkalinity rather than adding it.

Question 27Water treatment

What is the primary purpose of adding chlorine to treated water before it leaves the plant?

  1. To increase the alkalinity of the water
  2. To oxidize iron and manganese in the source
  3. To provide disinfection and a persistent residual Correct answer.
  4. To raise the pH of the finished water

Explanation

Chlorine applied at the plant disinfects the finished water and leaves a residual that continues to protect the distribution system against microbial regrowth. It does not serve as a pH or alkalinity adjustment chemical. Iron and manganese oxidation is a separate pretreatment step, not the purpose of final disinfection.

Question 28Water treatment

Which type of coagulant is most commonly used in municipal surface water treatment plants in North America?

  1. Aluminum sulfate (alum) Correct answer.
  2. Sodium fluoride
  3. Calcium hypochlorite
  4. Potassium permanganate

Explanation

Alum is the most widely used primary coagulant because it is effective, inexpensive, and well understood. It destabilizes negatively charged particles and forms floc that can be settled and filtered. The other listed chemicals serve fluoridation, oxidation, or disinfection roles.

Question 29Water treatment

Which unit process in a conventional surface water plant immediately follows flocculation?

  1. Recarbonation
  2. Filtration
  3. Granular activated carbon adsorption
  4. Sedimentation Correct answer.

Explanation

In the conventional treatment train, coagulation and flocculation are followed by sedimentation, where the floc settles out before filtration. Filtration comes after sedimentation as the final particle barrier. Recarbonation and carbon adsorption are separate processes used for specific water quality goals.

Question 30Water treatment

Which measurement is the standard field indicator of the effectiveness of the particle removal process in finished water?

  1. Conductivity
  2. Hardness
  3. Dissolved oxygen
  4. Turbidity Correct answer.

Explanation

Turbidity is a direct, low-cost surrogate for suspended particles and pathogens in finished water, and it is monitored continuously in most plants. Conductivity reflects dissolved ions, hardness reflects calcium and magnesium, and dissolved oxygen is not a treatment performance measure.

Question 31Water treatment

What does a positive coliform result in a distribution system sample most directly indicate?

  1. The water has excessive hardness
  2. Microbiological contamination or a loss of system integrity is possible Correct answer.
  3. The chlorine residual is too high
  4. The filter media has failed

Explanation

Coliforms are indicator organisms, and a positive result signals possible contamination or a breach such as a cross-connection, main break, or loss of residual. It triggers follow-up sampling and investigation rather than a single simple fix. Hardness, high residual, and filter media are unrelated to a coliform result.

Question 32Water treatment

Which chemical is commonly used to fluoridate drinking water?

  1. Ferric chloride
  2. Fluorosilicic acid Correct answer.
  3. Sodium bicarbonate
  4. Sodium hypochlorite

Explanation

Fluorosilicic acid is the most widely used fluoridation chemical in large systems, with sodium fluoride and sodium fluorosilicate also used. Sodium hypochlorite is a disinfectant, sodium bicarbonate raises alkalinity, and ferric chloride is a coagulant.

Question 33Water treatment

What is the purpose of the backwash step in a rapid sand filter?

  1. To disinfect the filter media permanently
  2. To add coagulant to the filter influent
  3. To increase the filter run length by compacting the media
  4. To remove accumulated particles and restore the media bed Correct answer.

Explanation

Backwashing reverses flow upward through the bed, expanding the media and flushing out trapped particles so the filter can be returned to service. It restores head loss and particle removal capacity. It does not compact media, dose coagulant, or permanently disinfect the bed.

Question 34Water treatment

A plant's raw water alkalinity is 180 mg/L as CaCO3 and the coagulant dose consumes 40 mg/L. What is the approximate alkalinity remaining after coagulation, assuming no other reactions?

  1. 220 mg/L
  2. 40 mg/L
  3. 180 mg/L
  4. 140 mg/L Correct answer.

Explanation

Alkalinity consumed by the coagulant is subtracted from the raw water value, so 180 minus 40 equals 140 mg/L as CaCO3. The remaining alkalinity buffers the water and helps keep pH from dropping excessively. Adding the two values or ignoring the consumption gives incorrect results.

Question 35Water treatment

A filter has a design loading rate of 4 gpm/ft2 and a surface area of 200 ft2. What is the design flow through the filter?

  1. 50 gpm
  2. 1,600 gpm
  3. 200 gpm
  4. 800 gpm Correct answer.

Explanation

Flow equals loading rate multiplied by surface area, so 4 gpm/ft2 times 200 ft2 equals 800 gpm. This calculation is used to check whether the filter is operating within its design capacity. Dividing the area by the rate or using the area alone gives the wrong answer.

Question 36Water treatment

An operator wants to determine the optimum coagulant dose for a new source water. Which test is most appropriate?

  1. A chlorine demand test
  2. A bacteriological membrane filtration test
  3. A hardness titration
  4. A jar test Correct answer.

Explanation

A jar test simulates coagulation, flocculation, and settling at several chemical doses so the operator can select the dose producing the clearest settled water. Chlorine demand, hardness titration, and bacteriological testing measure different water quality parameters and do not identify coagulant dose.

Question 37Water treatment

A plant uses free chlorine for primary disinfection. Which factor most strongly affects the CT value required to inactivate Giardia?

  1. The water temperature and pH Correct answer.
  2. The size of the clearwell inlet pipe
  3. The type of filter underdrain
  4. The color of the filter media

Explanation

CT (concentration times contact time) requirements depend strongly on temperature and pH because they affect the speciation and reactivity of free chlorine. Lower temperature and higher pH generally require greater CT for the same inactivation. Media color, pipe size, and underdrain type do not change the disinfection requirement.

Question 38Water treatment

An operator measures a free chlorine residual of 0.2 mg/L at a distant point in the distribution system while the plant effluent is 1.0 mg/L. What is the most likely explanation?

  1. The pH at the plant is too high
  2. The filter is passing too many particles
  3. The water temperature at the plant is too low
  4. Chlorine is decaying along the pipe due to reactions with pipe surfaces and organics Correct answer.

Explanation

Free chlorine residual declines with travel time and distance as it reacts with pipe wall material, biofilm, and dissolved organics. A large drop from plant to distant point indicates chlorine decay in the system. Plant temperature, pH, and filter performance do not directly explain a localized low residual far from the plant.

Question 39Water treatment

A softening plant treats water with 250 mg/L total hardness as CaCO3 and targets 80 mg/L. How much hardness must be removed?

  1. 250 mg/L
  2. 170 mg/L Correct answer.
  3. 80 mg/L
  4. 330 mg/L

Explanation

The hardness to remove is the difference between the influent and target values, so 250 minus 80 equals 170 mg/L as CaCO3. This value drives the lime and soda ash dose calculations. Using the target alone or adding the values gives the wrong amount.

Question 40Water treatment

Why is a minimum chlorine residual maintained throughout the distribution system rather than only at the plant?

  1. To improve the aesthetic quality of the water
  2. To provide continuous protection against contamination that may enter downstream Correct answer.
  3. To reduce the turbidity of the water
  4. To increase the hardness of the water

Explanation

A residual carried into the distribution system provides ongoing disinfection against microbial contamination introduced by main breaks, cross-connections, or regrowth. It is a barrier after the plant, not a treatment for aesthetics, hardness, or turbidity.

Question 41Water treatment

A plant's filtered water turbidity is 0.08 NTU and the finished water turbidity is 0.10 NTU. Which conclusion is most appropriate?

  1. Turbidity is within typical regulatory limits and performance is acceptable Correct answer.
  2. The clearwell is adding excessive turbidity
  3. The coagulant dose is far too high
  4. The filters are performing poorly and require immediate backwash

Explanation

Values near or below 0.1 NTU are consistent with good filtration and typical regulatory limits for filtered water. A small increase from filtered to finished water is common and not by itself a problem. Poor filter performance would show substantially higher values, and the data do not indicate a coagulant overdose.

Question 42Water treatment

What is the main purpose of adding a polymer as a filter aid?

  1. To reduce the alkalinity of the water
  2. To strengthen floc so it is captured more effectively by the filter Correct answer.
  3. To increase the pH of the filtered water
  4. To disinfect the filter media

Explanation

Filter aids are low-dose polymers that bind small particles into larger, stronger flocs that are more easily captured in the filter bed, improving effluent quality and lengthening runs. They do not adjust pH or alkalinity and are not disinfectants.

Question 43Water treatment

A rapid sand filter shows rising head loss and good effluent turbidity. What does this pattern most likely indicate?

  1. The media has been lost from the bed
  2. The coagulant dose is too low
  3. Particles are passing through the filter into the effluent
  4. Particles are being captured in the upper media and the filter needs backwashing Correct answer.

Explanation

Rising head loss with good effluent quality means the filter is effectively capturing particles, which accumulate and increase resistance to flow until backwash is needed. Particle passage would show as turbidity breakthrough, media loss would show as reduced bed depth, and a low coagulant dose would typically degrade effluent quality.

Question 44Water treatment

A plant must reduce disinfection byproduct formation while maintaining adequate disinfection. Which strategy best addresses this goal?

  1. Reducing filter backwash frequency
  2. Removing natural organic matter precursors before chlorination Correct answer.
  3. Raising the finished water pH before chlorination
  4. Increasing the chlorine dose before coagulation

Explanation

Disinfection byproducts such as trihalomethanes form when chlorine reacts with natural organic matter. Removing precursors through enhanced coagulation, sedimentation, and filtration before chlorination reduces formation. Increasing the chlorine dose or raising pH would tend to worsen or not solve the problem, and backwash frequency is unrelated.

Question 45Water treatment

Which statement best describes the role of the clearwell in a surface water plant?

  1. It provides contact time for disinfection and stores finished water Correct answer.
  2. It serves as the primary coagulation basin
  3. It removes dissolved gases from the water
  4. It backwashes the filters

Explanation

The clearwell stores filtered water and provides the contact time needed for disinfection before the water is pumped to the distribution system. It is not a gas removal unit, coagulation basin, or backwash facility.

Question 46Water treatment

A lime softening plant produces water with a pH of 10.5 after excess lime treatment. Why must this water be recarbonated?

  1. To remove chlorine residual
  2. To raise the pH further for disinfection
  3. To lower the pH and stabilize the water to prevent scale or corrosion Correct answer.
  4. To increase the calcium concentration

Explanation

Excess lime softening leaves the water supersaturated with calcium carbonate and at high pH. Recarbonation with carbon dioxide lowers the pH and converts excess hydroxide and carbonate so the water is stable and will not deposit scale or cause corrosion in the distribution system. It does not raise pH, add calcium, or remove chlorine.

Question 47Water treatment

A filter run ends after only 8 hours with high head loss, while the previous run lasted 30 hours. Which condition is the most likely cause?

  1. The backwash rate was too low to clean the bed
  2. The filter was returned to service without proper media conditioning
  3. The coagulant dose was increased and floc carryover overloaded the filter Correct answer.
  4. The raw water turbidity decreased significantly

Explanation

A sudden shortening of filter runs with high head loss commonly follows an increase in coagulant dose or poor floc formation that carries more solids onto the filter. A low backwash rate would leave the bed dirty but would typically show up as turbidity breakthrough as well. Clean media conditioning and lower raw turbidity would tend to lengthen, not shorten, runs.

Question 48Water treatment

An operator calculates that the required CT for Giardia inactivation at the current temperature and pH is 120 mg-min/L, and the measured residual is 1.5 mg/L. What minimum contact time is required?

  1. 120 minutes
  2. 80 minutes Correct answer.
  3. 40 minutes
  4. 180 minutes

Explanation

Contact time equals CT divided by the residual concentration, so 120 divided by 1.5 equals 80 minutes. This calculation verifies whether the clearwell provides sufficient detention time under current conditions. Using the CT value directly or dividing by the wrong number gives an incorrect time.

Question 49Water treatment

A plant using alum coagulation observes that pH drops sharply after coagulant addition and floc formation is poor. Which corrective action is most appropriate?

  1. Increase the alum dose to improve floc
  2. Increase the chlorine dose before coagulation
  3. Reduce the filter loading rate
  4. Add an alkaline chemical to restore pH and alkalinity Correct answer.

Explanation

Alum consumes alkalinity and releases hydrogen ions, lowering pH. When alkalinity is insufficient, pH falls outside the range where floc forms well, so adding an alkaline chemical such as lime or sodium hydroxide restores the buffering and improves coagulation. Increasing alum worsens the pH drop, and filter loading and prechlorination do not address the cause.

Question 50Water treatment

Which combination of observations best confirms that a filter is performing adequately after a media replacement?

  1. Low effluent turbidity and no head loss increase
  2. Low effluent turbidity, acceptable head loss development, and proper backwash expansion Correct answer.
  3. High backwash rate and short filter runs
  4. High effluent turbidity and rapid head loss

Explanation

Adequate filter performance after media replacement is confirmed by consistently low effluent turbidity, normal head loss development during the run, and proper bed expansion during backwash. High turbidity, no head loss change, or short runs indicate problems such as media loss, poor cleaning, or inadequate conditioning.