Wastewater Treatment Processes and Operations, Exams of Social Sciences

Download Wastewater Treatment Processes and Operations and more Exams Social Sciences in PDF only on Docsity! WASTEWATER GRADE III PRACTICE TEST A properly functioning anaerobic digester will achieve a reduction in volatile solids of greater than 50%. ( )True ( )False - Answers -True Explanation: A properly functioning anaerobic digester will achieve a reduction in volatile solids of greater than 50%. You are operating a belt press to dewater anaerobically digested sludge. The conditioned feed solids concentration today is 4.2%. You have operated for 7 hours at an average of 60 gpm. You have produced 22.4 wet weight tons of filter cake with an average solids concentration of 19%. Determine the percent solids recovery for today's operation. ( )93.3% ( )99.5% ( )91.5% ( )96.4% ( )94.1% - Answers -96.4% What is a likely result if the overflow rate is too low in a primary clarifier? ( )Primary sludge that is too thick to pump ( )Excessive scum ( )Floating sludge near the inlet end of the clarifier ( )Septic odors ( )Excessive load on the sludge cross collectors - Answers -Septic odors Explanation: Septic odors will occur if the overflow rate is too low in a primary clarifier. Which of the following is not true regarding chlorine or chlorination equipment? ( ) Due to the high vapor pressure of liquid chlorine, it may be withdrawn from a 1 ton container without pressurization ( )Chlorine gas may lower the pH of the secondary effluent ( )When taking a chlorinator out of service, the chlorine valve at the cylinder is shut and the chlorine ejector is operated for a time to remove the gas remaining in the line ( )The vacuum in a vacuum chlorinator is created when chlorine gas moves rapidly through a restriction in the line ( )The withdraw rate is limited because freezing in the line can occur if chlorine gas is removed too fast - Answers -The vacuum in a vacuum chlorinator is created when chlorine gas moves rapidly through a restriction in the line Explanation: The vacuum in a vacuum chlorinator is created by the use of carrier water flowing through the nozzles of an eductor. Which of the following will hinder photosynthesis? ( )Duckweed ( )Phosphorous ( )Nitrogen ( )Chlorophyll ( ) Sunlight - Answers -Duckweed Explanation: Duckweed will block sunlight from penetrating the surface of the pond and will thus hinder photosynthesis. Photosynthesis is a vital process in successful pond treatment. Two toxic gases that have a noxious odor and are commonly found in confined spaces are Carbon Dioxide and Ferrous Sulfide. ( )True ( )False - Answers -False Explanation: Carbon dioxide has no odor. The toxic gas with a distinct noxious odor is Hydrogen Sulfide. Which one of the following is true regarding the complete mix activated sludge treatment plant? ( )The rate of Oxygen uptake per pound of activated sludge is the same throughout the aeration basin ( )It uses bubble dome diffusers to ensure adequate DO for microorganisms ( )It is not possible to calculate MCRT for the system ( )Complete mixing is not desirable ( )Complete mix processes usually have 18-24 hour detention time in the aeration basin - Answers -The rate of Oxygen uptake per pound of activated sludge is the same throughout the aeration basin Explanation: With a complete mix system, the rate of oxygen uptake per pound of sludge is consistent throughout the aeration basin. Explanation: A High F/M ratio will cause a thick, white foam during the start-up of an activated sludge wastewater plant A 30 acre facultative pond is operated at a depth of 5 feet. The daily plant influent flow is 0.815 MGD with a BOD of concentration of 165 mg/L. a. Calculate the organic loading rate to this pond in lbs BOD/acre/day. b. How many days will it take to raise the level to 6 feet. (Assume flow remains constant and no flow is discharged until the new level is reached) ( )25.2 lbs BOD/acre/day ; 10 days ( )24.3 lbs BOD/acre/day ; 15 days ( )37.4 lbs BOD/acre/day ; 12 days ( )49 lbs BOD/acre/day ; 14 days ( )13 lbs BOD/acre/day ; 12 days - Answers -( ) 37.4 lbs BOD/acre/day ; 12 days Why should the under drain channel of a trickling filter only be half full during maximum hydraulic loading? ( )Control of psychoda ( Filter Flies) ( )Limit growth of certain nuisance organisms ( )Ensure adequate ventilation ( )Prevent slime growth ( )Reduce solids loading - Answers -( )Ensure adequate ventilation Advanced primary treatment involves adding coagulants, such as ferric chloride, to improve the removal of fine solids. ( )True ( )False - Answers -( )True Explanation: Advanced primary treatment involves adding coagulants, such as ferric chloride, to improve the removal of fine solids. Coagulants neutralize small charged particles and allow them to flocculate (stick together) which aids in settling. The measure of pH is of little value when determining the changing condition of an anaerobic digester because the alkalinity acts as a buffer to pH changes. ( )True ( )False - Answers -( )True Explanation: The measure of pH is of little value when determining the changing condition of an anaerobic digester because the alkalinity acts as a buffer to pH changes. An ORP probe must be installed in a chlorine contact chamber at a point that is 5 minutes downstream of the chlorine injection point when the plant is at its peak dry weather flow of 0.75 MGD. There are 4 passes in the CCB. Each pass is 45 feet long and 5.5 feet wide. The depth is 5 feet. How many feet from the injection point should the probe be installed? ( )9.5 ft ( )17.5 ft ( )22 ft ( )11.1 ft ( )12.7 ft - Answers -( )12.7 ft Find the percentage of volatile solids destroyed, given the following information about an anaerobic digester. Raw Sludge Feed Digested Sludge TS % = 5% TS % = 3.5% VS % = 78% VS % = 63% ( )39% ( )48% ( )58% ( ) 62% ( )52% - Answers -( )52% Changes in which of the following parameters would be least helpful when assessing the health of an anaerobic digester? ( )Volatile acid concentration ( )CO2 concentration ( )Gas production ( )pH ( )Bicarbonate alkalinity - Answers -( )pH Explanation: All other parameters listed will change before pH changes in a digester. A rising volatile acid to alkalinity ratio is an operators best indication of a digester going sour. A drop in pH is expected in an anaerobic digester that is being started with a normal load of raw sludge and a small amount of seed sludge. ( )True ( )False - Answers -( )True Explanation: A drop in pH is expected in an anaerobic digester that is being started with a normal load of raw sludge and a small amount of seed sludge. Step feed aeration is a process used in activated sludge treatment that involves adjusting the rate of aeration along the length of the aeration basin. ( )True ( )False - Answers -( )False Explanation: Step feed aeration is a process involves feeding the waste stream at different locations along the length of the aeration basin. Which one of the following tests is not used to assess the health of a primary anaerobic digester? ( )Percent methane ( )Total alkalinity ( )Volatile acid concentration ( )Percent hydrogen sulfide ( )Percent carbon dioxide - Answers -( )Percent hydrogen sulfide Explanation: Hydrogen sulfide is not measured and used to assess the health of an anaerobic digester. The other parameters listed are used to monitor a digesters health. Nitrification involves facultative bacteria reducing the nitrate ion and releasing nitrogen gas. ( )True ( )False - Answers -( )False Explanation: De-nitrification involves facultative bacteria reducing the nitrate ion and releasing nitrogen gas. SVI is defined as: ( )The rate of settling of mixed liquor during the 30 minute settling test ( )The volume occupied by one gram of MLSS after settling for 30 minutes in the sludge settle ability test ( )The volume of MLSS after settling for 30 minutes in the sludge settle ability test ( )The supernatant velocity index ( )None of the above - Answers -( )The volume of MLSS after settling for 30 minutes in the sludge settle ability test Explanation: The volume occupied by one gram of MLSS after settling for 30 minutes in the sludge settle ability test. The main reason a trickling filter flow is re-circulated is to dilute the influent waste stream. ( )True ( )False - Answers -( )False Explanation: The main reason trickling filter flow is recirculated is to maintain a constant hydraulic load on the filter. High rate trickling filters are typically designed to handle organic loads of 30-100 gpd/ft2. ( )True ( )False - Answers -( )False Explanation: Organic loading is measured in lbs of BOD/day/1,000 ft3. A high rate trickling filter is designed to handle an organic loading rate of 25-300 lbs of BOD/day/1,000 ft3. A large population of rotifers in the activated sludge is usually an indication of bulking. ( )True ( )False - Answers -( )False MCRT and the F/M ratio are directly related. (A short MCRT means a low F/M) ( )True ( )False - Answers -( )False Explanation: MCRT and the F/M ratio are INVERSELY related. (A SHORT MCRT means a HIGH F/M) INVERSELY = Opposite NPDES is an acronym for National Pollution Discharge Elimination System. ( )True ( )False - Answers -( )False Explanation: NPDES is an acronym for National POLLUTANT Discharge Elimination System. Sodium thiosulfate is often used to dechlorinate a secondary effluent BOD sample. ( )True ( )False - Answers -( )False Explanation: Secondary BOD samples generally do not contain chlorine, therefore there is no need to dechlorinate. The best indicator of the effectiveness of the disinfection process is: ( )HPC test ( )Coliform test ( )Effluent turbidity ( )Chlorine dose in ppm ( )Chlorine residual - Answers -( )Coliform test Explanation: The coliform test is used to monitor the effectiveness of the disinfection process. For a plant that uses the F/M ratio to control the activated sludge process, an increase in BOD or COD load requires an increase in microorganism mass. ( )True ( )False - Answers -( )True Explanation: For a plant that uses the F/M ratio to control the activated sludge process, an increase in BOD or COD load requires an increase in microorganism mass. High I/I (Infiltration and Inflow) can contribute to poor performance of the primary and secondary treatment systems. ( )True ( )False - Answers -( )True Explanation: High I/I (Infiltration and Inflow) can contribute to poor performance of the primary and secondary treatment systems. Explanation: High I/I (Infiltration and Inflow) can contribute to poor performance of the primary and secondary treatment systems. Which of the following is within normal operating range for a DAF thickening waste activated sludge using polymer? ( )A solids recovery value of 50% ( )A solids loading rate of 1.0 lbs/sq ft/hr ( )All of above values are normal ( )A floating solids concentration of 0.9% ( )Air to solids ratio of 2:1 - Answers -( )Air to solids ratio of 2:1 Explanation: Normal ranges for a DAF using polymer are: Air to solids ratio - 0.01-0.1 lbs/lbs; Solids loading rate - 24-48 lbs/day/ft2; Hydraulic loading - 0.5-2.0 gpm/ft2; Floating solids - 3%-5%; Solids recovery - 90% -98%. The solids loading rate given as an answer choice is converted to hours rather than days. 1 lbs/ft2/hour is the same as 24 lbs/day/ft2. Results for COD and BOD are normally very close to one another when sampling raw wastewater. ( )True ( )False - Answers -( )False Explanation: COD results are generally higher than BOD results. Higher surface loading rates result in lower removal efficiency for BOD and Suspended Solids. ( )True ( )False - Answers -( )True Explanation: Higher surface loading rates result in lower removal efficiency for BOD and Suspended Solids. What does endogenous respiration refer to? ( )A situation where there are too many microorganisms for the amount of available food and these organism use their own cell mass as a food source ( )Breathing that is made difficult due to excessive solids in the mixed liquor ( )Too little oxygen for the microorganisms ( )A modification of the activated sludge process in which the F to M ratio exceeds 0.5 ( )The release of phosphorous by bacteria due to insufficient DO - Answers -( )A situation where there are too many microorganisms for the amount of available food and these organism use their own cell mass as a food source Which of the following choices best describes the correct method to collect a coliform sample from a chlorinated effluent? ( )All of the above ( )Rinse the bottle three times before collecting the sample ( )Add sodium thiosulfate to the bottle prior to sterilization of the bottle ( )Collect a composite sample to ensure it is representative ( ) Completely fill the bottle so no air remains - Answers -( )Add sodium thiosulfate to the bottle prior to sterilization of the bottle Explanation: Sodium thiosulfate is added to remove the chlorine residual from a chlorinated coliform sample. This is done to ensure that any bacteria present will have an opportunity to grow and be measured. Over time, the chlorine residual will inactivate the bacteria present in the sample. A 0.5 percent polymer solution (dry weight) is fed at a dose of 2 ppm to a clarifier receiving a flow of 900 gpm. What should the polymer feed rate be in gallons per hour? ( )32.8 gal/hr ( )19.1 gal/hr ( )21.6 gal/hr ( )15.3 gal/hr ( )25.4 gal/hr - Answers -( )21.6 gal/hr The most likely cause of denitrification in an activated sludge plant is: ( )Not enough nitrifying bacteria ( )Pin-floc in the secondary clarifier ( )The ammonia concentration is too low ( )Keeping the settled mixed liquor in the secondary clarifier too long ( )Insufficient nitrates in the system - Answers -( )Keeping the settled mixed liquor in the secondary clarifier too long Explanation: Denitrification occurs when there is no dissolved oxygen for bacteria to use. Bacteria will use the oxygen combined with nitrogen (in the form of nitrite and nitrate) which results in the formation of nitrogen gas. The longer sludge remains in the secondary clarifier without oxygen, the higher the occurrence of floating sludge due to denitrification. You are working at a 5 MGD conventional activated sludge treatment plant. The aeration tank operates at a 35% return rate and is 1 MG in volume. A standard BOD test of the primary effluent provides the following results for 6 ml and 12 ml samples. 6 ml 12 ml Blank Initial DO 8.1 8.2 8.3 Final DO 5.6 3.0 8.2 a. What BOD value should be reported for this test? b. What is the organic loading in lbs BOD/Day/1,000 ft3 of aerator volume? ( )138 mg/L ; 31.9 lbs BOD/day/1,000 ft3 ( )128 mg/L ; 39.9 lbs BOD/day/1,000 ft3 ( )114 mg/L ; 19.9 lbs BOD/day/1,000 ft3 ( )128 mg/L ; 39.9 lbs BOD/day/1,000 ft3 ( )118 mg/L ; 24.5 lbs BOD/day/1,000 ft3 - Answers -( )128 mg/L ; 39.9 lbs BOD/day/1,000 ft3