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OR Water/Wastewater Operator practice questions

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Question 1Source Water Characteristics and Water Quality

Which source water type is generally most vulnerable to rapid turbidity changes after a heavy rain?

  1. Surface water Correct answer.
  2. A deep confined aquifer
  3. A bedrock artesian well
  4. A protected spring

Explanation

Surface waters receive direct runoff from their watersheds, so storms quickly carry soil and organic particles into rivers, streams, and reservoirs. Groundwater sources are usually shielded by soil and rock, which filter particles and moderate changes.

Question 2Source Water Characteristics and Water Quality

Turbidity in drinking water is most commonly expressed in which unit?

  1. NTU Correct answer.
  2. ppm
  3. mg/L
  4. uS/cm

Explanation

Turbidity is an optical measurement of light scattering and is reported in nephelometric turbidity units (NTU). Mass-based units such as mg/L and ppm do not describe light scattering, and uS/cm is used for conductivity.

Question 3Source Water Characteristics and Water Quality

Which pathogen is most resistant to standard free chlorine disinfection at typical doses and is a major concern in surface water supplies?

  1. Cryptosporidium Correct answer.
  2. Fecal coliform bacteria
  3. Enterococcus
  4. Giardia lamblia

Explanation

Cryptosporidium forms thick-walled oocysts that are highly resistant to typical free chlorine doses used in drinking water treatment. Giardia is also chlorine-resistant relative to many bacteria, but Cryptosporidium is the more chlorine-resistant protozoan of the two.

Question 4Source Water Characteristics and Water Quality

A water sample with a pH of 5.5 is best described as:

  1. Slightly basic
  2. Neutral
  3. Strongly basic
  4. Acidic Correct answer.

Explanation

The pH scale runs from 0 to 14, with 7 considered neutral. Values below 7 are acidic, and values above 7 are basic or alkaline.

Question 5Source Water Characteristics and Water Quality

Detection of total coliform bacteria in a raw surface water sample most directly indicates:

  1. A natural condition requiring no follow-up
  2. High calcium hardness
  3. A possible contamination problem Correct answer.
  4. Low chlorine demand

Explanation

Total coliforms are widely used indicator organisms because their presence suggests possible fecal contamination or a breakdown in treatment and distribution barriers. Their detection calls for investigation rather than automatic acceptance.

Question 6Source Water Characteristics and Water Quality

Water hardness is primarily caused by which dissolved ions?

  1. Sodium and potassium
  2. Calcium and magnesium Correct answer.
  3. Sulfate and chloride compounds
  4. Nitrate and phosphate

Explanation

Hardness is mainly caused by dissolved calcium and magnesium ions, which react with soap and can form scale. Sodium, potassium, chloride, sulfate, nitrate, and phosphate are not the primary hardness-causing ions.

Question 7Source Water Characteristics and Water Quality

Alkalinity in source water primarily measures the water's:

  1. Total dissolved solids content
  2. Capacity to neutralize acid Correct answer.
  3. Concentration of dissolved oxygen
  4. Number of suspended particles

Explanation

Alkalinity is the acid-neutralizing capacity of water, largely due to bicarbonate, carbonate, and hydroxide ions. It helps buffer pH changes and is distinct from dissolved oxygen, total dissolved solids, and particle counts.

Question 8Source Water Characteristics and Water Quality

Elevated nitrate in a rural groundwater supply is most often associated with:

  1. Fertilizer and septic waste Correct answer.
  2. Atmospheric acid deposition
  3. Road salt application
  4. Naturally occurring radon gas in bedrock

Explanation

Nitrate in rural groundwater commonly comes from agricultural fertilizer, animal waste, and septic system effluent that leach into the aquifer. High nitrate is a health concern, especially for infants.

Question 9Source Water Characteristics and Water Quality

Total organic carbon (TOC) in raw water is of concern mainly because it:

  1. Reduces the need for coagulation
  2. Forms disinfection byproducts Correct answer.
  3. Raises the pH of the water
  4. Increases calcium hardness

Explanation

Organic carbon reacts with disinfectants such as chlorine to form regulated disinfection byproducts, including trihalomethanes and haloacetic acids. Reducing TOC before disinfection helps control byproduct formation.

Question 10Source Water Characteristics and Water Quality

Iron in source water commonly causes which aesthetic problem?

  1. White scale deposits
  2. Red-brown staining of fixtures Correct answer.
  3. A soapy taste
  4. Blue-green staining of fixtures

Explanation

Iron dissolved in water can oxidize and precipitate as reddish-brown deposits that stain fixtures, laundry, and plumbing. Manganese tends to cause dark or black staining, while calcium carbonate scale is usually white.

Question 11Source Water Characteristics and Water Quality

Excessive nutrient loading in a lake most commonly leads to:

  1. Reduced pH buffering capacity
  2. Increased dissolved oxygen
  3. Algal blooms and eutrophication Correct answer.
  4. Lower turbidity and clearer water

Explanation

Phosphorus and nitrogen inputs can stimulate excessive algae and plant growth, a process called eutrophication. Decaying algae then consume oxygen and can create taste, odor, and treatment problems.

Question 12Source Water Characteristics and Water Quality

Groundwater under the direct influence of surface water (GWUDI) is best described as:

  1. A deep confined aquifer with no surface connection
  2. Groundwater with a direct surface-water connection Correct answer.
  3. Water with naturally high total dissolved solids
  4. Surface water that has been fully treated

Explanation

GWUDI refers to groundwater that is hydraulically connected to surface water and may be subject to pathogen contamination from that source. It often requires treatment similar to surface water.

Question 13Source Water Characteristics and Water Quality

In a stratified lake during summer, the hypolimnion typically has:

  1. Greater algal production
  2. Lower dissolved oxygen Correct answer.
  3. Higher pH values
  4. Warmer water temperatures

Explanation

The hypolimnion is the cooler, deeper layer that is isolated from the atmosphere and sunlight during stratification. Oxygen in that layer is consumed by decomposition and is not readily replenished, so dissolved oxygen tends to be lower.

Question 14Source Water Characteristics and Water Quality

Water is most likely to be corrosive when it has:

  1. High turbidity
  2. Low pH and low alkalinity Correct answer.
  3. High calcium hardness
  4. High alkalinity and high pH

Explanation

Low pH and low alkalinity reduce the water's buffering capacity and can make it aggressive toward metal and concrete surfaces. Such water may require pH adjustment or corrosion control treatment.

Question 15Source Water Characteristics and Water Quality

The yellowish-brown color of some raw surface waters is most often caused by:

  1. Minerals leached from concrete pipes
  2. Dissolved iron and manganese only
  3. Natural organic matter like tannins Correct answer.
  4. Suspended clay and silt particles

Explanation

Decaying vegetation releases natural organic matter, including tannins and humic substances, which impart a yellowish-brown color to many surface waters. This color is distinct from turbidity caused by suspended clay or silt.

Question 16Source Water Characteristics and Water Quality

Fluoride is sometimes adjusted in drinking water to:

  1. Control algae growth in reservoirs
  2. Remove nitrate from the water
  3. Soften hard water
  4. Reduce the risk of dental caries Correct answer.

Explanation

Fluoride is added at controlled concentrations to help prevent tooth decay. It is not used as an algicide, softener, or nitrate-removal treatment.

Question 17Source Water Characteristics and Water Quality

In disinfection, the CT value is calculated as:

  1. Concentration multiplied by contact time Correct answer.
  2. Temperature multiplied by contact time
  3. Disinfectant demand multiplied by turbidity
  4. Contact time divided by concentration

Explanation

CT is the product of disinfectant residual concentration (C) and contact time (T). It is used with organism-specific tables to estimate inactivation achieved under given conditions.

Question 18Source Water Characteristics and Water Quality

Cyanotoxins produced during a harmful algal bloom are of concern because they:

  1. They are destroyed by boiling
  2. They increase the buffering capacity of water
  3. They improve taste and odor
  4. They are toxic and treatment-resistant Correct answer.

Explanation

Some cyanotoxins can be toxic to humans and animals and may persist through conventional treatment processes. Boiling is not a reliable remedy because it can concentrate toxins as water evaporates.

Question 19Source Water Characteristics and Water Quality

A positive Langelier Saturation Index (LSI) generally indicates water that is:

  1. High in nitrate
  2. Scale-forming Correct answer.
  3. Exactly balanced
  4. Corrosive

Explanation

A positive LSI means the water is supersaturated with respect to calcium carbonate and tends to deposit scale. A negative index suggests undersaturation and a tendency toward corrosion.

Question 20Source Water Characteristics and Water Quality

Arsenic in Oregon groundwater is most commonly derived from:

  1. Leaking septic systems
  2. Natural geological deposits Correct answer.
  3. Agricultural fertilizer application
  4. Road salt storage

Explanation

Arsenic in groundwater is often released naturally from certain rocks and sediments, including volcanic and sedimentary deposits found in parts of Oregon. It is not primarily a fertilizer, road salt, or septic indicator.

Question 21Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What is the primary purpose of coagulation in a surface water treatment plant?

  1. To destabilize colloids so they can clump together Correct answer.
  2. To physically strain suspended solids out of the water
  3. To raise the pH of the water into the scaling range
  4. To oxidize dissolved organic matter into carbon dioxide

Explanation

Coagulant chemicals neutralize the negative surface charge that keeps colloids apart, allowing particles to approach one another and aggregate. Straining of solids is a filtration function, oxidation is a separate chemical step, and pH adjustment for scaling control is a different operation.

Question 22Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Which chemical is the most common primary coagulant used in North American surface water plants?

  1. Powdered activated carbon
  2. Sodium fluoride
  3. Sodium hypochlorite
  4. Aluminum sulfate (alum) Correct answer.

Explanation

Alum hydrolyzes in water to form positively charged aluminum species that destabilize negatively charged colloids. Hypochlorite is a disinfectant, powdered activated carbon is an adsorbent for taste and odor compounds, and fluoride is added for dental health.

Question 23Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What is the purpose of the rapid mix (flash mix) stage that precedes flocculation?

  1. To settle out the heaviest grit before treatment
  2. To let the filter media ripen
  3. To allow flocs to grow large enough to settle
  4. To disperse coagulant rapidly and evenly Correct answer.

Explanation

Rapid mix applies high shear for a short period, usually seconds to about a minute, so the coagulant is spread uniformly and hydrolysis products form throughout the flow. Floc growth occurs later in flocculation, and grit removal is handled in a separate grit chamber.

Question 24Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Flocculation is best described as:

  1. The settling of suspended particles under gravity
  2. Gentle, slow mixing that builds larger floc Correct answer.
  3. Rapid, violent stirring that breaks apart the floc
  4. Addition of chlorine to inactivate pathogens

Explanation

Flocculation uses gentle agitation, typically for 15 to 45 minutes at a low velocity gradient, so particles collide and stick together into larger, denser floc. Violent stirring shears floc apart, and settling is a separate downstream step.

Question 25Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

In a conventional treatment train, what is the main function of the sedimentation basin?

  1. To remove dissolved minerals such as calcium and magnesium
  2. To dissolve coagulant chemicals
  3. To disinfect the water with ultraviolet light
  4. To settle floc out before filtration Correct answer.

Explanation

The clarifier provides quiet conditions in which floc formed during flocculation settles to the bottom as sludge, reducing the solids load on the filters. Chemical dissolution occurs upstream in the rapid mix, and hardness removal is a softening function.

Question 26Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Which two ions are primarily responsible for the hardness of water?

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

Explanation

Hardness is conventionally defined as the sum of calcium and magnesium concentrations, expressed as calcium carbonate equivalents. Sodium and potassium are monovalent and are not counted as hardness, and chloride and sulfate are merely accompanying anions.

Question 27Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What is the dominant removal mechanism in a properly operating rapid sand filter?

  1. Volatilization of dissolved gases
  2. Chemical oxidation of contaminants
  3. Attachment to media grains and deposited solids Correct answer.
  4. Simple straining of particles larger than the pore spaces

Explanation

Most particles are far smaller than the pore openings, so removal depends on transport to the grain surfaces followed by attachment, aided by material already deposited in the bed. Straining captures only the largest particles.

Question 28Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

In lime softening, adding hydrated lime primarily removes which constituent?

  1. Calcium hardness Correct answer.
  2. Nitrate (NO3-)
  3. Total organic carbon (TOC)
  4. Dissolved oxygen (DO)

Explanation

Lime raises pH and supplies carbonate so dissolved calcium precipitates as calcium carbonate, which is removed as sludge. Magnesium requires a still higher pH, and lime does not remove nitrate or organic carbon.

Question 29Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Alum reacts with the natural bicarbonate alkalinity in the water. What is the main effect of that reaction?

  1. It produces alkalinity and raises the pH
  2. It uses up alkalinity and lowers pH Correct answer.
  3. It increases both alkalinity and dissolved oxygen
  4. It has no measurable effect on pH or alkalinity

Explanation

Alum consumes bicarbonate and releases carbon dioxide and sulfate, which depresses pH; roughly 0.45 mg/L of alkalinity as CaCO3 is used per mg/L of alum. Where alkalinity is too low, lime or soda ash must be added to complete the reaction.

Question 30Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

A jar test is used to pick the optimum coagulant dose. Which observation most directly identifies that dose?

  1. The longest time for floc to form
  2. Clearest supernatant with well-formed floc Correct answer.
  3. The largest pH increase after dosing
  4. The highest turbidity reading after slow mixing

Explanation

The jar test simulates rapid mix, flocculation, and settling at several doses; the best dose yields the clearest supernatant with a good settleable floc in a reasonable time. High residual turbidity points to underdosing or overdosing, not to the optimum.

Question 31Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

A settling basin receives 4.0 MGD and has a surface area of 10,000 ft2. What is the surface overflow rate?

  1. 40 gpd/ft2
  2. 4,000 gpd/ft2
  3. 250 gpd/ft2
  4. 400 gpd/ft2 Correct answer.

Explanation

Surface overflow rate equals flow divided by surface area: 4,000,000 gpd divided by 10,000 ft2 gives 400 gpd/ft2. Basin depth affects detention time but does not enter this calculation.

Question 32Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Detention time in a settling basin is calculated as:

  1. Weir length divided by flow rate
  2. Flow rate multiplied by basin depth
  3. Surface area divided by flow rate
  4. Basin volume divided by flow rate Correct answer.

Explanation

Detention time is the basin volume divided by the flow rate, giving the average time a parcel of water spends in the basin. Surface overflow rate, by contrast, is flow divided by surface area and has units of velocity.

Question 33Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

The velocity gradient (G) in a flocculation basin is a measure of:

  1. The concentration of coagulant in the water
  2. The shear intensity of the applied mixing Correct answer.
  3. The settling velocity of the floc particles
  4. The head loss through the filter bed

Explanation

G, expressed in reciprocal seconds, quantifies the mixing energy per unit volume and therefore the shear that promotes particle collisions. Flocculation is usually tapered from a higher G to a lower G so floc grows without being broken apart.

Question 34Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

A dual-media filter normally has which arrangement, from top to bottom?

  1. Garnet over sand over anthracite
  2. Sand over gravel over anthracite
  3. Activated carbon over gravel
  4. Anthracite coal over sand Correct answer.

Explanation

Anthracite is less dense and coarser than sand, so backwashing stratifies it on top, producing coarse-to-fine filtration that lets solids penetrate deeper into the bed. Garnet is the densest medium and is used as the bottom layer in a multimedia bed.

Question 35Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

During backwash of a rapid sand filter, the bed is typically expanded by approximately:

  1. 0 to 5 percent
  2. 10 to 15 percent
  3. 100 to 150 percent
  4. 20 to 50 percent Correct answer.

Explanation

Design backwash rates expand the bed about 20 to 50 percent, which lets grains collide and scrub off attached solids while the dirt is carried to the wash troughs. Too little expansion leaves media dirty, and too much washes media to waste.

Question 36Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Near the end of a filter run, which condition typically signals that the filter must be backwashed?

  1. Media grains dissolve and soften the water
  2. Head loss drops and effluent turbidity falls
  3. The filter bed expands and the flow reverses
  4. Head loss reaches its limit and turbidity may rise Correct answer.

Explanation

Captured solids clog the bed, so head loss climbs until it reaches the terminal value; if the filter is not backwashed first, turbidity breaks through into the effluent. Either condition is a trigger to end the run.

Question 37Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

In lime-soda softening, which chemical supplies the carbonate needed to remove noncarbonate hardness such as calcium sulfate?

  1. Sodium chloride
  2. Soda ash Correct answer.
  3. Hydrated lime alone
  4. Sulfuric acid

Explanation

Lime removes carbonate hardness, but calcium associated with sulfate or chloride needs an added carbonate source, which soda ash provides. Lime alone cannot remove noncarbonate hardness because there is no bicarbonate present to convert.

Question 38Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Which statement correctly describes a sodium-cycle ion exchange softener?

  1. It removes hardness with a reverse osmosis membrane
  2. It swaps sodium for calcium and magnesium Correct answer.
  3. It removes hardness by boiling the water
  4. It precipitates hardness as a sludge for disposal

Explanation

Resin in the sodium form gives up two sodium ions for each calcium or magnesium ion taken out of the water, and the resin is regenerated with brine. Hardness leaves in the regenerant waste rather than as a precipitate in the treated water.

Question 39Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Most clay colloids in raw water carry a negative surface charge. Why does coagulation make them settle?

  1. The coagulant raises the pH above the point of zero charge
  2. The positive charge of the colloids attracts the coagulant
  3. Positive coagulant species neutralize colloid charge Correct answer.
  4. Heat released by the reaction drives particles together

Explanation

Hydrolysis products of alum or ferric salts are positively charged and adsorb onto the negative colloids, lowering the electrostatic barrier so van der Waals attraction can bind them together. Coagulation is charge neutralization, not heating or pH raising.

Question 40Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Which material is commonly added as a coagulant aid to add weight and strength to floc?

  1. Sodium hypochlorite
  2. An anionic polymer Correct answer.
  3. Potassium permanganate
  4. Hydrated lime

Explanation

Polymers bridge between particles and dense clays add nuclei, producing larger, heavier, more shear-resistant floc that settles faster. Lime adjusts pH, while hypochlorite and permanganate are oxidants that act on other constituents.

Question 41Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What condition is required to remove magnesium hardness by lime softening?

  1. Addition of sodium chloride
  2. Saturation with carbon dioxide gas
  3. A lower pH of about 6.0
  4. Excess lime to pH 10.5 to 11 Correct answer.

Explanation

Magnesium precipitates as magnesium hydroxide only at elevated pH, so plants dose lime past the calcium endpoint to about pH 10.5 to 11. The water is then recarbonated to bring the pH back down and stabilize it.

Question 42Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

Settling of discrete, nonflocculating particles whose velocity stays constant as they fall is classified as:

  1. Type IV settling
  2. Type III settling
  3. Type I settling Correct answer.
  4. Type II settling

Explanation

Type I is discrete particle settling described by Stokes' law, as in grit removal. Type II is flocculent settling, Type III is hindered or zone settling, and Type IV is compression settling within the sludge blanket.

Question 43Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

In a multimedia filter, media are selected by both grain size and specific gravity. Which bed arrangement is correct?

  1. Sand on top of garnet with anthracite at the bottom
  2. Anthracite, then sand, then garnet Correct answer.
  3. Anthracite (SG about 1.4) below sand (SG about 2.65)
  4. Garnet (SG about 4.0) above anthracite (SG about 1.4)

Explanation

Backwash stratification places the lightest, coarsest media on top and the densest on the bottom, so anthracite over sand over garnet gives coarse-to-fine filtration. This lets solids penetrate deeper and lengthens filter runs.

Question 44Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

A plant doses 40 mg/L of alum. Approximately how much natural alkalinity (as CaCO3) will the alum consume?

  1. About 40 mg/L
  2. About 2 mg/L
  3. About 18 mg/L Correct answer.
  4. About 90 mg/L

Explanation

Alum consumes roughly 0.45 mg/L of alkalinity as CaCO3 per mg/L of alum dosed, so 40 mg/L of alum uses about 18 mg/L of alkalinity. If the raw water contains less than that, lime or soda ash must be fed to complete the reaction.

Question 45Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

After excess-lime softening, the water is recarbonated with carbon dioxide. What is the purpose?

  1. To disinfect the water and oxidize organics
  2. To increase the hardness above the target
  3. To lower pH and stabilize the water Correct answer.
  4. To raise the pH further and precipitate sodium

Explanation

Recarbonation converts residual hydroxide and carbonate to bicarbonate, lowering pH so the water will not deposit calcium carbonate scale in filters or distribution piping. It also helps produce a stable, noncorrosive finished water.

Question 46Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What is the primary purpose of the rapid-mix (flash-mix) step in a coagulation treatment train?

  1. To strip dissolved gases such as carbon dioxide from the water
  2. To disperse the coagulant quickly so it contacts particles before floc can form Correct answer.
  3. To scrape settled solids from the floor of the settling basin
  4. To grow large, settleable floc particles that will settle in the basin

Explanation

Rapid mix delivers intense agitation for a short period, typically seconds, so the coagulant is dispersed throughout the water and destabilization begins before any floc forms. The intensity and short duration prevent the fragile floc from being sheared apart later.

Question 47Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

In a slow sand filter, what is the schmutzdecke?

  1. The gravel bed that supports the filter sand
  2. The clearwell that stores finished water
  3. The troughs that carry away backwash water
  4. The biological mat that develops on the media surface Correct answer.

Explanation

A slow sand filter develops a thin biological layer of algae, bacteria, and trapped material on the surface of the sand. This layer does most of the particle and microorganism removal, and the filter is taken out of service and skimmed when it becomes too thick.

Question 48Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What is the function of the graded gravel layer placed beneath the sand in a rapid sand filter?

  1. It supports the media and distributes backwash water evenly Correct answer.
  2. It adds calcium and magnesium to the finished water
  3. It traps air released from solution during filtration
  4. It removes the very fine particles that pass through the sand

Explanation

The gravel supports the weight of the media and prevents it from being lost through the underdrain, while its graded layers spread backwash water uniformly across the bottom of the bed. Without it, backwash would channel through the underdrain openings and leave part of the bed unexpanded.

Question 49Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

What is the purpose of the flocculation step that follows coagulation?

  1. To promote particle collisions that build settleable floc Correct answer.
  2. To raise the pH of the coagulated water before settling
  3. To disinfect the water before it reaches the filters
  4. To oxidize color-causing compounds with a strong oxidant

Explanation

Flocculation uses gentle, prolonged mixing so that destabilized particles collide and stick together, growing into floc large enough to settle or be captured by a filter. The mixing must be slow enough to encourage contact without breaking up the floc that has formed.

Question 50Water Treatment Processes (coagulation, flocculation, sedimentation, filtration, softening)

A plant treats 2.0 MGD and feeds alum at a dose of 30 mg/L. What is the daily alum feed rate?

  1. 500 lb/day Correct answer.
  2. 5,000 lb/day
  3. 1,000 lb/day
  4. 250 lb/day

Explanation

The feed rate in pounds per day equals dose in mg/L times flow in MGD times 8.34, the weight in pounds of one gallon of water times the unit conversion. Here, 30 x 2.0 x 8.34 equals about 500 lb/day.