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PE Environmental practice questions

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Question 1Air Quality

How many criteria pollutants are subject to National Ambient Air Quality Standards under the Clean Air Act?

  1. Four
  2. Six Correct answer.
  3. Five
  4. Seven

Explanation

The Clean Air Act requires NAAQS for six criteria pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. Primary standards protect public health, while secondary standards protect public welfare.

Question 2Air Quality

What is the purpose of a primary National Ambient Air Quality Standard?

  1. Protect only sensitive ecosystems in Class I areas
  2. Protect public welfare from effects such as visibility impairment and crop damage
  3. Protect public health with an adequate margin of safety Correct answer.
  4. Limit emissions from new major stationary sources

Explanation

Primary NAAQS are set to protect public health, including the health of sensitive groups, with an adequate margin of safety. Secondary standards address public welfare effects such as visibility, crops, and materials.

Question 3Air Quality

Which averaging form is used for the current 8-hour ozone National Ambient Air Quality Standard?

  1. 24-hour average
  2. Annual arithmetic mean
  3. 1-hour maximum, not to be exceeded more than once per year
  4. Fourth-highest 8-hour maximum averaged over 3 years Correct answer.

Explanation

The ozone NAAQS is based on the annual fourth-highest daily maximum 8-hour average concentration, averaged over three consecutive years. This form smooths year-to-year variability while targeting peak exposures.

Question 4Air Quality

At 25 degrees Celsius and 1 atmosphere, what concentration in micrograms per cubic meter corresponds to 1 ppm of sulfur dioxide?

  1. 2,620 µg/m³ Correct answer.
  2. 262 µg/m³
  3. 1,310 µg/m³
  4. 655 µg/m³

Explanation

At 25 degrees Celsius and 1 atmosphere, one mole of ideal gas occupies about 24.45 liters, so micrograms per cubic meter equals ppm times molecular weight divided by 24.45. For sulfur dioxide with a molecular weight of 64, 1 ppm is about 2,620 micrograms per cubic meter.

Question 5Air Quality

What is the dominant particle collection mechanism in a fabric filter baghouse?

  1. Filtration through the fabric and dust cake Correct answer.
  2. Electrostatic charging and collection on plates
  3. Absorption of particles into a scrubbing liquid
  4. Centrifugal separation of particles from the gas stream

Explanation

In a fabric filter, gas passes through the fabric and the accumulated dust cake, which does most of the particle capture. Cleaning removes the cake periodically to control pressure drop.

Question 6Air Quality

What is the form and level of the National Ambient Air Quality Standard for lead?

  1. 0.50 µg/m³, annual average
  2. 15 µg/m³, 24-hour average
  3. 1.5 µg/m³, quarterly average
  4. 0.15 µg/m³, rolling 3-month average Correct answer.

Explanation

The lead NAAQS is 0.15 micrograms per cubic meter, measured as a rolling 3-month average. It was revised in 2008 to protect public health near sources such as smelters and airports.

Question 7Air Quality

Which federal program created the first large cap-and-trade system for sulfur dioxide emissions from electric utilities?

  1. New Source Review
  2. Acid Rain Program Correct answer.
  3. Regional Haze Program
  4. Title V Operating Permit Program

Explanation

Title IV of the 1990 Clean Air Act Amendments created the Acid Rain Program, a cap-and-trade system for sulfur dioxide emissions from electric utilities. It was designed to reduce acid deposition at lower cost.

Question 8Air Quality

Which of the following is a secondary air pollutant?

  1. Sulfur dioxide emitted from a coal boiler
  2. Lead from a smelter
  3. Ozone formed from NOx and VOCs Correct answer.
  4. Carbon monoxide from a vehicle tailpipe

Explanation

Ozone is not emitted directly in significant amounts; it forms in the atmosphere when nitrogen oxides and volatile organic compounds react in sunlight. Sulfur dioxide, carbon monoxide, and lead are emitted directly and are primary pollutants.

Question 9Air Quality

A new stationary source that is not in a listed source category locates in an area attaining the NAAQS. What potential emission rate makes it a major source subject to PSD review?

  1. 100 tpy
  2. 500 tpy
  3. 50 tpy
  4. 250 tpy Correct answer.

Explanation

For PSD, a new source outside the listed source categories is major at 250 tons per year of any regulated pollutant. Sources in the listed categories have a 100 ton per year threshold.

Question 10Air Quality

New Source Review in a nonattainment area requires which emission limit for a major new source?

  1. BACT, best available control technology
  2. MACT, maximum achievable control technology
  3. LAER, lowest achievable emission rate Correct answer.
  4. NSPS, new source performance standards

Explanation

Nonattainment NSR requires LAER plus emission offsets and certification that other sources in the state are in compliance. BACT applies in attainment and unclassifiable areas under PSD.

Question 11Air Quality

Which statement best describes how best available control technology is set for a PSD source?

  1. It applies only to hazardous air pollutants from major sources
  2. It must be the single most stringent emission limit achieved in practice anywhere in the world
  3. It is a fixed national limit published in 40 CFR Part 60
  4. It is set case-by-case after considering energy, environmental, and economic impacts Correct answer.

Explanation

BACT is determined case-by-case for each PSD source, taking into account energy, environmental, and economic impacts and other costs. It is not a nationally fixed limit and need not be the most stringent limit in existence.

Question 12Air Quality

A Title V operating permit must be renewed at what interval?

  1. Every 2 years
  2. Every 3 years
  3. Every 5 years Correct answer.
  4. Every 10 years

Explanation

Title V operating permits are issued for a fixed term of 5 years and must be renewed. The permit consolidates all applicable requirements for a major source.

Question 13Air Quality

Under the NESHAP program, a source is a major source of hazardous air pollutants if it emits which of the following?

  1. 100 tpy or more of any single HAP
  2. 10 tpy or more of any single HAP or 25 tpy or more of total HAP Correct answer.
  3. 25 tpy or more of any single HAP or 10 tpy or more of total HAP
  4. 5 tpy or more of any single HAP

Explanation

A major HAP source emits 10 tons per year or more of any single hazardous air pollutant, or 25 tons per year or more of total hazardous air pollutants. Area sources are below these thresholds.

Question 14Air Quality

What is the purpose of a State Implementation Plan?

  1. To issue federal operating permits to major sources
  2. To show how the state will attain and keep the NAAQS Correct answer.
  3. To set national ambient air quality standards
  4. To define MACT standards for HAP sources

Explanation

A State Implementation Plan is the state's plan, required by Clean Air Act Section 110, showing how it will attain and maintain each NAAQS. EPA reviews and approves the plan, and a federal plan can be imposed if the state fails to submit an adequate one.

Question 15Air Quality

In the Gaussian plume model, the ground-level centerline concentration at a fixed downwind distance is approximately proportional to which quantity?

  1. 1 divided by wind speed squared
  2. The square of wind speed
  3. 1 divided by wind speed Correct answer.
  4. Wind speed

Explanation

The Gaussian plume equation has wind speed in the denominator, so concentration varies roughly as 1 divided by wind speed at a fixed distance. Higher wind speed dilutes the plume, although it also affects plume rise and dispersion.

Question 16Air Quality

A facility processes 1,000 tons per year of material with an uncontrolled emission factor of 5 pounds per ton. A control device removes 90 percent of the emissions. What is the controlled emission rate?

  1. 5,000 lb/yr
  2. 50 lb/yr
  3. 500 lb/yr Correct answer.
  4. 4,500 lb/yr

Explanation

Uncontrolled emissions are 1,000 tons times 5 pounds per ton, or 5,000 pounds per year. Retaining 10 percent after 90 percent control gives 500 pounds per year.

Question 17Air Quality

How often must a certified continuous emission monitoring system normally undergo a relative accuracy test audit?

  1. Semi-annually
  2. Every 3 years
  3. Every 5 years
  4. Annually Correct answer.

Explanation

Under the federal CEMS quality assurance requirements, a relative accuracy test audit is performed annually, while other checks such as cylinder gas audits occur more frequently. The audit compares CEMS readings with reference method measurements.

Question 18Air Quality

The Regional Haze Rule sets what long-term goal for mandatory Class I federal areas?

  1. A 50 percent reduction in haze by 2020
  2. Zero visible emissions by 2030
  3. Compliance with the PM2.5 NAAQS by 2035
  4. Natural visibility conditions by 2064 Correct answer.

Explanation

The Regional Haze Rule sets the goal of restoring natural visibility conditions in mandatory Class I federal areas by 2064, with progress measured over 10-year periods. States adopt plans to reduce haze-causing emissions.

Question 19Air Quality

Which compound is excluded from the regulatory definition of volatile organic compounds because of negligible photochemical reactivity?

  1. Toluene
  2. Xylene
  3. Propane
  4. Methane Correct answer.

Explanation

EPA's VOC definition excludes methane and certain other compounds with negligible photochemical reactivity. Propane, toluene, and xylene are VOCs that participate in ozone formation.

Question 20Air Quality

Under the Clean Air Act, good engineering practice stack height is generally the greater of 65 meters or which value?

  1. 3 times the building height
  2. 2.5 times the building height Correct answer.
  3. The building height plus 10 meters
  4. 1.5 times the building height

Explanation

Good engineering practice stack height is defined as the greater of 65 meters or 2.5 times the height of nearby structures, with additional provisions for terrain. Credit for stack height above good engineering practice is generally not allowed in air quality modeling.

Question 21Air Quality

A continuous ground-level release has an emission rate of 100 g/s. At a downwind distance where the wind speed is 5 m/s, σy is 50 m, and σz is 30 m, the effective release height is 50 m. Using the Gaussian plume equation with ground reflection, what is the ground-level centerline concentration?

  1. 4,240 µg/m³
  2. 2,120 µg/m³
  3. 1,060 µg/m³ Correct answer.
  4. 265 µg/m³

Explanation

With the receptor on the centerline at ground level, the concentration is Q times the exponential term divided by pi times wind speed times σy times σz. Substituting the values gives about 0.00106 g/m³, or 1,060 µg/m³.

Question 22Air Quality

A fabric filter has an inlet dust loading of 10.0 gr/dscf and an outlet loading of 0.01 gr/dscf. What is the collection efficiency?

  1. 99.9% Correct answer.
  2. 90.0%
  3. 99.5%
  4. 99.0%

Explanation

Efficiency equals inlet minus outlet, divided by inlet, times 100. For these loadings, (10.0 minus 0.01) divided by 10.0 times 100 gives 99.9 percent.

Question 23Air Quality

A Class II area has a 24-hour PM10 PSD increment of 30 µg/m³. The baseline concentration is 40 µg/m³, and the current design value is 52 µg/m³. How much increment remains available for new sources?

  1. 18 µg/m³ Correct answer.
  2. 30 µg/m³
  3. 22 µg/m³
  4. 12 µg/m³

Explanation

Consumed increment is the current concentration minus the baseline, or 52 minus 40 equals 12 micrograms per cubic meter. Remaining increment is 30 minus 12 equals 18 micrograms per cubic meter.

Question 24Air Quality

For a Gaussian plume with ground-level reflection, a fixed effective stack height H, and the usual assumption that the ratio of σy to σz is constant, the maximum ground-level centerline concentration occurs where σz equals which value?

  1. H
  2. H/2
  3. H divided by √2 Correct answer.
  4. √2 times H

Explanation

Differentiating the ground-level concentration with respect to downwind distance and setting it to zero gives σz equal to H divided by the square root of 2. This is why maximum ground-level impact often occurs closer than the final plume centerline height.

Question 25Air Quality

A toxic air pollutant has an inhalation unit risk of 1×10⁻⁶ per µg/m³. If the lifetime average concentration at a receptor is 0.5 µg/m³, what is the estimated excess lifetime cancer risk?

  1. 5×10⁻⁴
  2. 5×10⁻⁶
  3. 5×10⁻⁷ Correct answer.
  4. 5×10⁻⁵

Explanation

Excess risk equals unit risk times lifetime average concentration. Multiplying 1×10⁻⁶ per µg/m³ by 0.5 µg/m³ gives 5×10⁻⁷.

Question 26Air Quality

What is the essential difference between a primary and a secondary National Ambient Air Quality Standard?

  1. Primary standards limit major-source emissions; secondary standards limit area-source emissions.
  2. Primary standards apply only in nonattainment areas; secondary standards apply only in attainment areas.
  3. Primary standards are federally enforceable; secondary standards are advisory only.
  4. Primary standards protect public health; secondary standards protect public welfare. Correct answer.

Explanation

The Clean Air Act requires primary NAAQS to protect public health with an adequate margin of safety and secondary NAAQS to protect public welfare, including visibility, crops, and materials. Both types of standards are enforceable. The distinction is the protected endpoint, not the source category or attainment status.

Question 27Air Quality

An Air Quality Index (AQI) value of 100 generally corresponds to which condition?

  1. The level of the annual average National Ambient Air Quality Standard
  2. The level of the shortest-term National Ambient Air Quality Standard Correct answer.
  3. The level that triggers State Implementation Plan revision
  4. The threshold for a nonattainment designation

Explanation

By design, an AQI of 100 corresponds to the level of the shortest-term NAAQS for the pollutant, with higher AQI values indicating concentrations above that standard. The AQI is a health communication tool and does not itself determine attainment status or SIP revisions.

Question 28Air Quality

Which of the following is a criteria pollutant under the Clean Air Act?

  1. Carbon monoxide (CO) Correct answer.
  2. Nitrous oxide (N2O)
  3. Methane (CH4)
  4. Carbon dioxide (CO2)

Explanation

The criteria pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. Carbon dioxide, methane, and nitrous oxide are greenhouse gases but are not criteria pollutants.

Question 29Air Quality

In the Pasquill-Gifford stability classification, which class represents the most unstable atmospheric conditions?

  1. Class B
  2. Class F
  3. Class A Correct answer.
  4. Class D

Explanation

The Pasquill-Gifford classes range from A (very unstable) through D (neutral) to F (stable). Class A produces the strongest vertical mixing and the greatest plume dispersion.

Question 30Air Quality

A moderate ozone nonattainment area is generally required to attain the 8-hour ozone NAAQS within how many years after designation?

  1. 6 years Correct answer.
  2. 9 years
  3. 3 years
  4. 15 years

Explanation

The Clean Air Act classifies ozone nonattainment areas with attainment deadlines that lengthen with severity: marginal (3 years), moderate (6 years), serious (9 years), severe (15 or 17 years), and extreme (20 years). A moderate area therefore has a 6-year deadline.

Question 31Air Quality

Thermal NOx formation in combustion is most strongly promoted by which set of conditions?

  1. Low flame temperature and fuel-rich conditions
  2. High flame temperature and high excess oxygen Correct answer.
  3. High fuel nitrogen content and low flame temperature
  4. Low excess oxygen and short residence time

Explanation

Thermal NOx forms through high-temperature reactions between atmospheric nitrogen and oxygen, so it increases sharply with flame temperature and available oxygen. Residence time at high temperature also increases thermal NOx. Fuel nitrogen content primarily affects fuel NOx rather than thermal NOx.

Question 32Air Quality

In selective catalytic reduction (SCR) of NOx, what reagent is typically injected into the flue gas?

  1. Lime slurry
  2. Ammonia or urea Correct answer.
  3. Sodium bicarbonate
  4. Activated carbon

Explanation

SCR injects ammonia, or urea that decomposes to ammonia, to react with NOx over a catalyst and form nitrogen and water. Lime slurry and sodium bicarbonate are acid-gas reagents, and activated carbon is used for adsorption rather than SCR.

Question 33Air Quality

In a fabric filter baghouse, operating at a higher air-to-cloth ratio than designed generally results in which condition?

  1. Reduced need for pulse cleaning
  2. Lower pressure drop and longer bag life
  3. Higher pressure drop and increased bag wear Correct answer.
  4. Higher collection efficiency for submicron particles

Explanation

The air-to-cloth ratio is the gas flow rate per unit of cloth area. A higher ratio forces more gas through each unit of fabric, raising the pressure drop and increasing abrasion and bag wear. It does not improve submicron capture or reduce cleaning demand.

Question 34Air Quality

An electrostatic precipitator typically has its lowest fractional collection efficiency for particles in which size range?

  1. Greater than 10 µm
  2. 0.1 to 1 µm Correct answer.
  3. Less than 0.01 µm
  4. 5 to 10 µm

Explanation

ESP collection efficiency is lowest in the submicron range around 0.1 to 1 µm, where particle charging and migration velocity are relatively poor. Larger particles are charged more effectively, and very small particles can be captured by diffusion.

Question 35Air Quality

Why is isokinetic sampling required when measuring particulate matter in a stack?

  1. To keep the sample filter below 100°F
  2. To remove moisture from the sample stream
  3. To cool the sample gas before it enters the filter
  4. To match nozzle velocity to stack gas velocity Correct answer.

Explanation

Isokinetic sampling means the gas velocity entering the sample nozzle equals the stack gas velocity. This prevents inertial bias, which would otherwise over- or under-sample coarse particles. Cooling, filter temperature, and moisture removal are separate sampling considerations.

Question 36Air Quality

An emission factor of 5 lb of pollutant per ton of material processed means that:

  1. 5 lb pollutant per ton of material, uncontrolled Correct answer.
  2. 5 tons of pollutant per ton of material processed
  3. 5 percent removal required by the control device
  4. 5 lb of material processed per pound of pollutant emitted

Explanation

Emission factors express mass of pollutant released per unit of activity, such as pounds per ton of material processed. Unless stated otherwise, published factors are typically uncontrolled and must be adjusted for control efficiency.

Question 37Air Quality

In a VOC-limited ozone nonattainment area, which strategy is generally most effective for reducing local ozone formation?

  1. Reduce NOx emissions only
  2. Increase NOx emissions to titrate ozone
  3. Reduce VOC emissions Correct answer.
  4. Take no action because ozone is regional

Explanation

In VOC-limited regimes, ozone formation is more sensitive to VOC availability than to NOx. Reducing NOx alone can sometimes increase local ozone by decreasing NOx titration, so VOC controls are generally more effective.

Question 38Air Quality

Compared with an unstable atmosphere, a stable atmosphere causes a continuous elevated plume to:

  1. Spread more rapidly vertically and dilute faster
  2. Remain narrower vertically and travel farther before dispersing Correct answer.
  3. Produce higher ground-level concentrations directly at the stack base
  4. Loop upward and downward near the stack

Explanation

Stable conditions suppress vertical mixing, so the plume spreads less in the vertical direction and remains coherent farther downwind. Unstable conditions enhance vertical mixing and dilute the plume more rapidly.

Question 39Air Quality

For an existing major source category, the MACT floor under the NESHAP program is generally based on:

  1. The single best-performing source in the category
  2. Average of the best-performing 12 percent of sources Correct answer.
  3. The average of all sources in the category
  4. The worst-performing 12 percent of sources

Explanation

For existing sources, the MACT floor is the average emission limitation achieved by the best-performing 12 percent of sources in the category, or the best five sources if there are fewer than 30. New-source MACT floors are based on the best controlled similar source.

Question 40Air Quality

Which Clean Air Act provision requires facilities handling threshold quantities of toxic or flammable substances to develop a risk management plan?

  1. Section 112(r) chemical accident prevention Correct answer.
  2. Title V operating permit program
  3. Prevention of Significant Deterioration under Section 165
  4. New Source Performance Standards under Section 111

Explanation

Clean Air Act Section 112(r) requires facilities with regulated substances above threshold quantities to develop and implement risk management plans. Title V is a permitting program, Section 111 sets new-source performance standards, and PSD governs air quality permitting in attainment areas.

Question 41Water Quality

A wastewater sample is diluted with seeded dilution water so that the mixture contains 1 part sample to 9 parts dilution water. The initial dissolved oxygen (DO) of the diluted mixture is 8.0 mg/L and the final DO after 5 days is 4.0 mg/L. Ignoring seed correction, what is the BOD5 of the sample?

  1. 400 mg/L
  2. 40 mg/L Correct answer.
  3. 0.4 mg/L
  4. 4.0 mg/L

Explanation

BOD5 is the DO depletion divided by the volumetric fraction of sample in the diluted mixture. The depletion here is 8.0 - 4.0 = 4.0 mg/L and the sample fraction is 1/10 = 0.10. Therefore BOD5 = 4.0 / 0.10 = 40 mg/L.

Question 42Water Quality

Which federal statute is the primary basis for requiring NPDES permits for point source discharges of pollutants to waters of the United States?

  1. Clean Water Act Correct answer.
  2. Resource Conservation and Recovery Act
  3. Toxic Substances Control Act
  4. Safe Drinking Water Act

Explanation

The Clean Water Act prohibits discharge of pollutants to waters of the United States without a permit and establishes the NPDES permitting program. The other statutes address drinking water, solid and hazardous waste, and industrial chemicals respectively.

Question 43Water Quality

Which group of organisms is most widely used as the indicator of recent fecal contamination when monitoring drinking water sources and recreational waters?

  1. Iron-oxidizing bacteria
  2. Nitrifying bacteria
  3. Fecal coliform bacteria Correct answer.
  4. Sulfate-reducing bacteria

Explanation

Fecal coliforms, and E. coli in particular, originate in the intestines of warm-blooded animals and are shed in high numbers in feces, so their presence signals recent fecal contamination. They are also inexpensive and reliable to enumerate in culture-based tests.

Question 44Water Quality

What is the principal function of a primary clarifier in a municipal wastewater treatment plant?

  1. Oxidizing dissolved organic matter with diffused air
  2. Removing settleable and floatable solids by gravity Correct answer.
  3. Converting ammonia to nitrate with nitrifying bacteria
  4. Disinfecting effluent with chlorine or ultraviolet light

Explanation

Primary treatment is physical: gravity settling removes settleable solids while skimming removes floatable material, typically reducing TSS by 50 to 65 percent and BOD5 by 25 to 40 percent. Biological oxidation, nitrification, and disinfection occur in later process steps rather than in the primary clarifier.

Question 45Water Quality

Under the Safe Drinking Water Act, a maximum contaminant level (MCL) is best described by which of the following?

  1. A recommended sampling frequency for systems
  2. An enforceable limit on contaminant concentration Correct answer.
  3. A non-enforceable health goal for contaminants
  4. A required minimum removal rate for treatment

Explanation

An MCL is the enforceable maximum permissible concentration of a contaminant in water delivered by a public water system, set as close to the health goal as is feasible with best available technology. The non-enforceable health goals are the maximum contaminant level goals (MCLGs).

Question 46Water Quality

In most freshwater lakes and reservoirs, which nutrient most commonly limits algal growth and is therefore the target of eutrophication control programs?

  1. Potassium
  2. Calcium
  3. Phosphorus Correct answer.
  4. Silica

Explanation

Phosphorus is typically the limiting nutrient for algal growth in freshwater because nitrogen is usually abundant relative to phosphorus demand. Nitrogen more often limits growth in estuaries and coastal marine waters.

Question 47Water Quality

A trickling filter is best classified as which type of biological wastewater treatment process?

  1. Attached-growth anaerobic process
  2. Attached-growth aerobic process Correct answer.
  3. Suspended-growth aerobic process
  4. Suspended-growth anaerobic process

Explanation

In a trickling filter, microorganisms grow as a biofilm attached to rock or plastic media while wastewater trickles over the surface, and oxygen is supplied by air drawn through the bed. The process is therefore attached-growth and aerobic, unlike activated sludge, which is suspended-growth.

Question 48Water Quality

At constant pressure, how does the saturation concentration of dissolved oxygen in water change as the water temperature increases?

  1. It first increases, then decreases, peaking near 25 C
  2. It decreases as temperature increases Correct answer.
  3. It increases steadily with temperature
  4. It stays constant because oxygen is nonpolar

Explanation

Gas solubility falls as temperature rises, so warmer water holds less dissolved oxygen; saturation is about 9.1 mg/L at 20 C versus about 7.6 mg/L at 30 C. This is why warm summer conditions combined with high organic loads are most stressful for aquatic life.

Question 49Water Quality

An activated sludge aeration basin holds 2,000 m3 of mixed liquor at an MLSS concentration of 2,500 mg/L. Sludge is wasted at 100 m3/d with a waste sludge suspended solids concentration of 8,000 mg/L, and solids leaving in the secondary effluent are negligible. What is the solids retention time (SRT)?

  1. 6.25 days Correct answer.
  2. 0.16 days
  3. 2.5 days
  4. 12.5 days

Explanation

SRT equals the mass of solids held in the system divided by the mass of solids leaving per day. The inventory is 2,000 m3 x 2.5 kg/m3 = 5,000 kg, and wasting removes 100 m3/d x 8 kg/m3 = 800 kg/d, giving 5,000 / 800 = 6.25 days.

Question 50Water Quality

An activated sludge system receives 10,000 m3/d of influent with a BOD5 of 200 mg/L. The aeration basin volume is 2,000 m3 and the MLVSS is 2,500 mg/L. What is the food-to-microorganism (F/M) ratio?

  1. 4.00 d-1
  2. 0.10 d-1
  3. 2.50 d-1
  4. 0.40 d-1 Correct answer.

Explanation

F/M is the mass of substrate entering per day divided by the mass of viable biomass in the aeration basin. The food is 10,000 m3/d x 0.20 kg/m3 = 2,000 kg/d and the biomass is 2,000 m3 x 2.5 kg/m3 = 5,000 kg, so F/M = 0.40 d-1.