Operation of Wastewater Treatment Plants (Level 1 Exam Prep)

Operation of Wastewater Treatment Plants (Level 1 Exam Prep) An Imhoff cone is used to measure________solids. A. suspended B. colloidal C. volatile D. settleable Ans- D. settleable (Operation of Wastewater Treatment Plants, Volume 1 by Kenneth D. Kerri) A _____ flume is widely used for measuring wastewater flow. Ans- Parshall (Operation of Wastewater Treatment Plants, Volume 1 by Kenneth D. Kerri) Velocity of flow in a grit channel must be reduced to a range of ____ to _____ fps in order for grit to properly settle. Ans- .7 to 1.4 fps (Operation of Wastewater Treatment Plants, Volume 1, 3.33 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 ______. Ans- 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. Ans- 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. Ans- 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) Ans- 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? Ans- 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? Ans- 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. Ans- 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 Ans- Facultative ponds are 4-8 feet deep (New Mexico Wastewater Systems Operator Certification Study Manual) Wastewater treatment ponds: Anaerobic ponds are _____ feet deep Ans- Anaerobic ponds are 14 feet in depth (New Mexico Wastewater Systems Operator Certification Study Manual) Typical Primary Clarifier Efficiencies: Settleable Solids expected removal efficiency _____% to _____% Ans- 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 _____% Ans- 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 _____% AnsTypical 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 _____% Ans- 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 Ans- 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 Ans- 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. Ans- 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. Ans- 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 Ans- 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. AnsTotal 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 Ans- Typical operating parameters for conventional activated sludge systems: MLSS in aeration basin = mg/L What is the main difference between sludge from primary and secondary clarifiers? Ans- 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? Ans- • 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 5.16 by Kenneth D. Kerri) What are some causes of black and odorous septic wastewater in primary clarifier effluent? Ans- • 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 5.16 by Kenneth D. Kerri