Operation of Wastewater Treatment Plants: Comprehensive Guide for Wastewater Professionals, Exams of Water and Wastewater Engineering

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An Imhoff cone is used to measure solids. A. suspended B. colloidal C. volatile D. settleable ✔✔D. settleable (Operation of Wastewater Treatment Plants, Volume 1 by Kenneth D. Kerri) A flume is widely used for measuring wastewater flow. ✔✔Parshall (Operation of Wastewater Treatment Plants, Volume 1 by Kenneth D. Kerri)

Operation of Wastewater Treatment Plants (Level 1 Exam Prep)

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Velocity of flow in a grit channel must be reduced to a range of to fps in order for grit to properly settle. ✔✔.7 to 1.4 fps (Operation of Wastewater Treatment Plants, Volume 1, 3. by Kenneth D. Kerri) With respect to grit removal systems, grit is traditionally defined as particles larger than 0.21mm (0.008 in) (65 mesh) and with a specific gravity of greater than. ✔✔specific gravity of grit is 2.65 or greater (EPA Wastewater Technology Fact Sheet, Screening and Grit Removal) Mechanically cleaned bar screens feature bars set at to degrees from vertical. ✔✔Bars set at 0 to 30 degrees from vertical. (EPA Wastewater Technology Fact Sheet, Screening and Grit Removal)

Manually cleaned bar screens feature bars set at _ to degrees from vertical to facilitate cleaning. ✔✔Bars set at 30 to 45 degrees from vertical to facilitate cleaning. Primarily used in older or smaller treatment facilities, or in bypass channels. (EPA Wastewater Technology Fact Sheet, Screening and Grit Removal) The BOD test measures the amount of oxygen that is consumed while a sample of wastewater is incubated in the dark at a temperature of °C for days (± hours) ✔✔The BOD test measures the amount of oxygen that is consumed while a sample of wastewater is incubated in the dark at a temperature of 20 °C for 5 days (± 3 hours) (USGS Book 9 - A7 (Third Edition) Five-Day Biochemical Oxygen Demand) What do we mean by Total Dissolved Solids (TDS) in wastewater? ✔✔All the solids that cannot be filtered out of the water (New Mexico Wastewater Systems Operator Certification Study Manual)

What do we mean by Total Suspended Solids (TSS) in wastewater? ✔✔All the solids that can be filtered out including: settleable solids and non-settleable solids (colloids) (New Mexico Wastewater Systems Operator Certification Study Manual) The wastewater in a sewer line should move at a speed that will prevent the deposition and buildup of solids in the sewer; this is called a "scouring velocity". A minimum velocity of fps provides this scouring or self-cleaning velocity. ✔✔The wastewater in a sewer line should move at a speed that will prevent the deposition and buildup of solids in the sewer; this is called a "scouring velocity". A minimum velocity of 2 fps provides this scouring or self-cleaning velocity. (New Mexico Wastewater Systems Operator Certification Study Manual) Wastewater treatment ponds: Facultative ponds are feet deep ✔✔Facultative ponds are 4 - 8 feet deep (New Mexico Wastewater Systems Operator Certification Study Manual)

Wastewater treatment ponds: Anaerobic ponds are feet deep ✔✔Anaerobic ponds are > feet in depth (New Mexico Wastewater Systems Operator Certification Study Manual) Typical Primary Clarifier Efficiencies: Settleable Solids expected removal efficiency % to % ✔✔Typical Primary Clarifier Efficiencies: Settleable Solids expected removal efficiency 95% to 99% (New Mexico Wastewater Systems Operator Certification Study Manual) Typical Primary Clarifier Efficiencies: Suspended Solids expected removal efficiency % to % ✔✔Typical Primary Clarifier Efficiencies: Suspended Solids expected removal efficiency 40% to 60% (New Mexico Wastewater Systems Operator Certification Study Manual)

Typical Primary Clarifier Efficiencies: Total Solids expected removal efficiency % to % ✔✔Typical Primary Clarifier Efficiencies: Total Solids expected removal efficiency 10% to 15% (New Mexico Wastewater Systems Operator Certification Study Manual) Typical Primary Clarifier Efficiencies: Biochemical Oxygen Demand (BOD) expected removal efficiency % to % ✔✔Typical Primary Clarifier Efficiencies: Biochemical Oxygen Demand (BOD) expected removal efficiency 20% to 50% (New Mexico Wastewater Systems Operator Certification Study Manual) Sludge septicity in the primary clarifier can be recognized when: A. sludge gasification causes large clumps of sludge to float on the water surface. B. Primary clarifier foam is black

C. The Specific Oxygen Uptake Rate (SOUR) in the primary clarifier is greater than 3000 mg O2/L/hr D. The sludge contains from 4.0 to 8.0 percent dry solids in TS laboratory testing E. All of the above ✔✔A. sludge gasification causes large clumps of sludge to float on the water surface. Pump cavitation may be caused by: A. Loss of discharge pressure due to open hy-drants or line breaks B. Closed suction valve C. Obstruction in the suction line D. Low suction head due to drop in water level E. All of the above ✔✔E. All of the above

(New Mexico Wastewater Systems Operator Certification Study Manual) A minimum dissolved oxygen (D.O.) level of mg/L is recommended in the aeration tank for most basic types of activated sludge processes. ✔✔A minimum dissolved oxygen (D.O.) level of 1.0 mg/L is recommended in the aeration tank for most basic types of activated sludge processes. Maintaining > 1.0 mg/L of D.O. contributes to establishing a favorable environment for the organisms, which produces the desired type of organism and the desired level of activity. (New Mexico Wastewater Systems Operator Certification Study Manual) If the D.O. in the aeration tank is allowed to drop too low for long periods, undesirable organisms, such as may develop and overtake the process. ✔✔If the D.O. in the aeration tank is allowed to drop too low for long periods, undesirable organisms, such as filamentous type bacteria may develop and overtake the process. (New Mexico Wastewater Systems Operator Certification Study Manual) Typical operating parameters for conventional activated sludge systems:

Detention time in aeration basin = hrs ✔✔Typical operating parameters for conventional activated sludge systems: Detention time in aeration basin = 4- 8 hrs (New Mexico Wastewater Systems Operator Certification Study Manual) Total solids consist of and solids, both of which contain organic and inorganic matter. ✔✔Total solids consist of dissolved and suspended solids, both of which contain organic and inorganic matter. (Operation of Wastewater Treatment Plants, Volume 1 by Kenneth D. Kerri) Typical operating parameters for conventional activated sludge systems: MLSS in aeration basin = - mg/L ✔✔Typical operating parameters for conventional activated sludge systems: MLSS in aeration basin = 1000 - 4000 mg/L

What is the main difference between sludge from primary and secondary clarifiers? ✔✔The main difference between the sludge from primary and secondary clarifiers is that the primary sludge is usually denser than secondary sludge. (Operation of Wastewater Treatment Plants, Volume 1, question 5.0A by Kenneth D. Kerri) What are some causes of floating sludge (bulking) in a primary clarifier? ✔✔• Sludge decomposing in tank, lifted by gasification

• Sludge collection mechanism, or flights are off
• Insufficient sludge removal
• Sludge blanket too deep
• Sludge pump runs but discharges thin or no sludge
• Sludge collector is damaged or needs adjusting (Operation of Wastewater Treatment Plants, Volume 1, section 5. by Kenneth D. Kerri)

What are some causes of black and odorous septic wastewater in primary clarifier effluent? ✔✔• Improper sludge removal

• Faulty sludge pump
• Sludge withdrawal line plugged
• Sludge collector worn or damaged
• Short circuiting through tank (Operation of Wastewater Treatment Plants, Volume 1, section 5. by Kenneth D. Kerri) List the basic laboratory tests used to determine clarifier efficiency. ✔✔The basic laboratory tests used to determine clarifier efficiency are DO, settleable solids, pH, temperature, BOD, suspended solids, chlorine residual (if needed), and coliform group bacteria (if needed). (Operation of Wastewater Treatment Plants, Volume 1, section 5.2A by Kenneth D. Kerri) Primary treatment is effective in removing (a) , and (b) , but is not nearly as effective in removing (c) , which may exert a strong oxygen

demand on the receiving waters. ✔✔Primary treatment is effective in removing (a) settleable solids, and (b) scum or floatable solids, but is not nearly as effective in removing (c) lighter suspended solids or dissolved solids, which may exert a strong oxygen demand on the receiving waters. (Operation of Wastewater Treatment Plants, Volume 1, section 6.0A by Kenneth D. Kerri) The major consideration for daily operation of a trickling filter is to use the recirculation rates that will produce good results (meet NPDES permit requirements), but not cause ponding and other problems. ✔✔The major consideration for daily operation of a trickling filter is to use the lowest recirculation rates that will produce good results (meet NPDES permit requirements), but not cause ponding and other problems. (Operation of Wastewater Treatment Plants, Volume 1, section 6.4A by Kenneth D. Kerri) Trickling filter recirculation rates should be adjusted to maintain a DO from to mg/L in the filter effluent from rock media and from to mg/L in the filter effluent from synthetic media. ✔✔Trickling filter recirculation rates should be adjusted to maintain a DO

from 3 to 6 mg/L in the filter effluent from rock media and from 4 to 8 mg/L in the filter effluent from synthetic media. (Operation of Wastewater Treatment Plants, Volume 1, section 6.4B by Kenneth D. Kerri) The tiny, gnat-sized filter fly is known also as? ✔✔Psychoda (Operation of Wastewater Treatment Plants, Volume 1, section 6. by Kenneth D. Kerri) Trickling filter flies can be controlled by what methods? ✔✔1. Increasing the recirculation rate

2. Keeping orifice openings clear, including end gates of the distributer arms
3. Applying approved insecticides with caution to filter walls and other plant structures
4. Flooding the filter for 24 hours at intervals frequent enough to prevent completion of the life cycle
5. Dosing with about 1 mg/L chlorine for a few hours each week
6. Keeping the area around the filter clean, including removing weeds, cutting grass, and pruning shrubbery

(Operation of Wastewater Treatment Plants, Volume 1, section 6.4F by Kenneth D. Kerri) True or False: A trickling filter should be taken out of service during icy conditions? ✔✔A trickling filter should not be taken out of service during icing conditions because the quality of the effluent will be reduced and additional maintenance problems could develop (Operation of Wastewater Treatment Plants, Volume 1, section 6.4G by Kenneth D. Kerri) MPN is the of coliform-group organisms per unit volume of sample water. Expressed as a density of population of organisms per mL of sample water. ✔✔MPN is the Most Probable Number of coliform-group organisms per unit volume of sample water. Expressed as a density of population of organisms per 100 mL of sample water. (Operation of Wastewater Treatment Plants, Volume 1, section 7. by Kenneth D. Kerri)

What is the RPM rate in which RBC units rotate? ✔✔1.5 RPM (Operation of Wastewater Treatment Plants, Volume 1, section 7. by Kenneth D. Kerri) For rotating biological contactors, what is the approximate percentage of media surface immersed in wastewater while in operation? ✔✔40% (Operation of Wastewater Treatment Plants, Volume 1, section 7. by Kenneth D. Kerri) Why is the RBC process divided into four or more stages? ✔✔The RBC process is divided into four or more stages to increase the effectiveness of a given amount of media surface area. Organisms on the first-stage media are exposed to high levels of BOD and reduce the BOD at a high rate. As the BOD levels decrease from stage to stage, the rate at which the organisms can remove BOD decreases and nitrification starts. (Operation of Wastewater Treatment Plants, Volume 1, section 7.0B by Kenneth D. Kerri)

Nitrification in nature is a two-step oxidation process of ammonium (NH4+) or ammonia (NH3) to nitrate (NO3−) catalyzed by two ubiquitous bacterial groups. The first reaction is oxidation of ammonium to nitrite by ammonia oxidizing bacteria represented by the (a.) genus. The second reaction is oxidation of nitrite (NO2−) to nitrate by nitrite-oxidizing bacteria, represented by the (b.) genus. ✔✔(a.) Nitrosomonas, (b.) Nitrobacter is an aerobic process in which bacteria change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate). The second-stage BOD is sometimes referred to as the "nitrogenous BOD" (first-stage BOD is called the "carbonaceous BOD"). ✔✔Nitrification is an aerobic process in which bacteria change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate). The second-stage BOD is sometimes referred to as the "nitrogenous BOD" (first-stage BOD is called the "carbonaceous BOD"). (Operation of Wastewater Treatment Plants, Volume 1, section 7. by Kenneth D. Kerri) is the anoxic biological reduction of nitrate nitrogen to nitrogen gas. ✔✔Denitrification is the anoxic biological reduction of nitrate nitrogen to nitrogen gas. In secondary clarifiers the

nitrogen bubbles produced as a result of denitrification can attach to the biological floc and float the floc to the surface. This condition is often the cause of rising sludge. (Operation of Wastewater Treatment Plants, Volume 1, section 7. by Kenneth D. Kerri) The stage is a stage of decomposition that occurs in the biological treatment processes when aerobic bacteria, using dissolved oxygen, change carbon compounds to carbon dioxide. ✔✔The carbonaceous stage is a stage of decomposition that occurs in the biological treatment processes when aerobic bacteria, using dissolved oxygen, change carbon compounds to carbon dioxide. (Operation of Wastewater Treatment Plants, Volume 1, section 7. by Kenneth D. Kerri) If the DO is too high in an aeration basin, may form and the secondary clarification process may not be able to remove the. ✔✔If the DO is too high in an aeration basin, "pinpoint" floc may form and the secondary clarification process may not be able to remove the "pin" floc.

(Operation of Wastewater Treatment Plants, Volume 1, section 8. by Kenneth D. Kerri) At what point of the day do wastewater stabilization ponds have the lowest pH? ✔✔Late night & early morning. Diurnal variations of both pH and dissolved oxygen are found in wastewater treatment ponds. During the day, algae use carbon dioxide which raises the pH while at night they produce carbon dioxide and the pH is lowered. (Operation of Wastewater Treatment Plants, Volume 1, section 9. by Kenneth D. Kerri) How is oxygen produced by algae? ✔✔Algae produce oxygen from the oxygen in the carbon dioxide molecule (CO2) through photosynthesis (Operation of Wastewater Treatment Plants, Volume 1, section 9.3A by Kenneth D. Kerri)

True or False: A facultative treatment pond is seeded with specially selected algae to optimize the treatment process for the climate and conditions. ✔✔False. Algae simply appear in a pond on their own without seeding. They are found in soil, water, and air and multiply under favorable conditions. (Operation of Wastewater Treatment Plants, Volume 1, section 9.3B by Kenneth D. Kerri) What does a definite green color in a treatment pond indicate? ✔✔A definite green color in a pond indicates a flourishing algal population and is a good sign. (Operation of Wastewater Treatment Plants, Volume 1, section 9.5C by Kenneth D. Kerri) When should a wastewater treatment pond be started? ✔✔Ponds should be started during the warmer months because higher temperatures are associated with efficient treatment processes. (Operation of Wastewater Treatment Plants, Volume 1, section 9.5B by Kenneth D. Kerri)

What should be done if the pH and DO in a pond are dropping dangerously low? ✔✔Check the loading. The loading may need to be reduced or stopped. Recirculating the water from a healthy pond to the problem pond should help the situation. Recirculation from outlet to inlet areas is beneficial for seeding, DO, and mixing. (Operation of Wastewater Treatment Plants, Volume 1, section 9.6L by Kenneth D. Kerri) What is the maximum daily withdrawal rate of chlorine gas used for wastewater disinfection, from a one ton cylinder? ✔✔400 lbs. The maximum withdrawal rate of chlorine gas from a 100/150 pound cylinder is 40 pounds per day; for a ton container, this rate is 400 pounds per day. True or False: pH generally will be affected significantly by a clarifier. ✔✔False. pH generally will NOT be affected significantly by a clarifier. (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions # by Kenneth D. Kerri)

True or False: Be sure to overlubricate clarifier equipment. ✔✔False. Be sure to NOT overlubricate clarifier equipment. (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #16 by Kenneth D. Kerri) True or False: Trickling filters with plastic media may be loaded at much higher rates than those with rock media without developing plugging, ponding, fly, or odor problems. ✔✔True. (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #19 by Kenneth D. Kerri) True or False: When starting a trickling filter, slime growth will start to develop on the filter media immediately. ✔✔False. It will only appear after several days. (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #21 by Kenneth D. Kerri) Which treatment units in a wastewater treament plant are designed and operated to remove sludge and scum?

A. Headworks basins B. Pre-aeration treatment units C. Preliminary treatment units D. Primary treatment units ✔✔D. Primary treatment units (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #2 by Kenneth D. Kerri) When evaluating trickling filter operation records, operators should adjust the process according to which main principle?

1. To minimize all operational costs
2. To obtain the best possible results for the least cost
3. To use the least amount of cholorine
4. To use the lowest recirculation rates ✔✔2. To obtain the best possible results for the least cost (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #2

by Kenneth D. Kerri) What could be the cause of the RBC media appearing black and producing odors that are not normal?

1. Industrial discharges containing sulfur compounds
2. Influent wastewater containing toxic or inhibitory substances
3. Solids or BOD overloading
4. Solids or BOD underloading ✔✔3. Solids or BOD overloading (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #23 by Kenneth D. Kerri) How can foaming be controlled in an aeration tank?
5. By increasing aeration rates
6. By introducing foam-devouring organisms
7. By removing detergents

4. By water sprays ✔✔4. water sprays (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #26 by Kenneth D. Kerri) When a pond turns dull green, gray, or colorless what condition is generally indicated?
5. The loading is satisfactory and the pond is working properly
6. The pH and DO are too high
7. The pH and DO have dropped too low
8. The pH is steady and weather conditions have deteriorated ✔✔3. The pH and DO have dropped too low (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #34 by Kenneth D. Kerri) How can an operator locate a small chlorine leak? By using a paint brush or rag dipped in

1. Caustic soda
2. Hydrochloric acid
3. Hypochlorite
4. Strong ammonia solution ✔✔4. Strong ammonia solution (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #38 by Kenneth D. Kerri) The concerns of the treatment plant designer and operator usually are to remove which substances in the wastewater?
5. Dissolved inorganic solids
6. Dissolved organic solids
7. Organic and inorganic solids
8. Radioactive wastes
9. Thermal wastes ✔✔2, 3 (Operation of Wastewater Treatment Plants, Volume 1, comprehensive review questions #4