TCEQ Wastewater Exam A Study Guide, Exams of Nursing

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Describe proper design of force main wastewater lines - correct answers Minimum 2 fps velocity with the smallest pump operating alone. Minimum 4 inch diameter pipe 150 psi rating. What is Standard Dimension Ratio? - correct answers Ratio of outside pipe diameter (OD) to wall thickness (PVC) Describe proper design of gravity wastewater lines. - correct answers Designed to flow half full under normal conditions at a minimum of 2 fps maximum of 10 fps. A primary clarifier should remove how much BOD and TSS? - correct answers 30% to 40% BOD 50% to 70 % TSS What is a wastewater outfall line? - correct answers Main line that carries the wastewater to the treatment plant. What are the minimum slopes for pipe sizes six, eight, ten, and 12 inches? What are these slopes designed to achieve? - correct answers 6 inch - 0.50 ft slope per 100 ft 8 inch - 0.33 ft slope per 100 ft 10 inch - 0.25 ft slope per 100 ft 12 inch - 0.20 ft slope per 100 ft

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You have 3900 feet of 10-inch pipe on a grade of 0.25. What is the elevation difference from one end to the other? - correct answers 3900/100 = 39 sections of pipe 39 ( 39 x 0.25 = 9.75 ft = 9 ft 9 inc A 12-inch line is on a 0.20 foot/100 foot grade. Point A is at an elevation of 127.6 feet. Point B is 600 feet downstream of point A and point C is 500 feet downstream of point B. What is the elevation of points B and C? - correct answers A = 127. 600 600 x (.2 ft / 100 ft) = 1.2 ft B = 127.6 - 1.2 = 126.4 ft 500 x (.2ft/100ft) = 1 ft C = 126.4-1= 125. List two methods of establishing grades when laying wastewater lines? - correct answers a. string and rod b. batter boards c. lasers A 20-inch pipe is flowing at 4000 GPM. What is the velocity in the pipe? - correct answers CFS = (pipe area (sq^2)) x (Velocity (fps)) 4000 gpm / 449 gpm/cfs = 8.91 cfs R = (20/12)/2 = 0. sq ft = 3.14 (0.833)^2 = 2.18 ft^ 8.91 = 2.18 ft x V = V = 8.91/2. V(FPS) = 4.

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Define infiltration and inflow. Give some examples of each. - correct answers Infiltration is water entering wastewater lines around joints, bad taps, or other small holes in the pipe caused by roots, etc. Infiltration usually occurs from ground water. Inflow is the direct flow of storm water into the system from direct connections of roof drains, etc., bad manholes, large openings in pipe such as old concrete pipe, or direct connections to storm water lines. What are some common methods for detecting leaks in a wastewater collection system? - correct answers a. infiltration/exfiltration testing b. low pressure air c. smoke testing d. television e. dye testing Manholes should have a minimum opening of _________ and be at least _________ wide. The invert depth should be at least ________ the diameter of the pipe. - correct answers 24 inches 4 ft 1/ What is the normal DO range in the aeration basin of an activated sludge plant? - correct answers 2.0 to 4.0 mg/L absolute minimum of 1.0 mg/L Which activated sludge process can operate the aeration basin below 2.0 mg/L D.O.? Explain why. - correct answers Extended

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aeration or racetracks. This process keeps the bugs starving and holds them for a longer time. (Endogenous growth phase) List several methods of wastewater flow measurements - correct answers a. V notch or rectangular weirs b. Parshall flumes c. Ultrasonic d. Venturi e. Magmeter What size pipe is needed to carry 6.5 MGD at a velocity of 2.0 FPS flowing half full? - correct answers CFS = (pipe area (sq^2)) x (Velocity (fps)) CFS = pi * (r^2) * fps 6.5 mgd x 694.4 gpm/mgd = 4514 gpm 4514 gpm / 449 gpm/cfs = 10.5 cfs x 2 fps = 21 cfs 21 CFS = pi x r^2 x 2 FPS r ^2 = 21 CFS / (pi x 2 FPS) r^2 = 21/ ( 3.14 x 2) =21 / (6.28) = 3.34 sq ft (r^2)^(1/2) = (3.34 ft ^2)^ 1/2 = 1.83 ft r = 1.83 ft convert to inches 1.83 ft x 12 in/ft = 21.96 in diameter = r * 2 d = 21.96 * 2 = 43.

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44 inch pipe is needed The Venturi meter works on what principle? - correct answers The Venturi meter works on Bertinelli's Principle. If you increase velocity there will be a decrease in pressure. Hydrogen sulfide results from what? - correct answers Anaerobic decomposition of sulfur compounds What are Bacilli? - correct answers Rod shaped bacteria How can odors in the collection system be controlled? - correct answers a. chlorine b. hydrogen peroxide c. masking agents What are cleanouts in the collection system used for? - correct answers Used for visual inspection of flows and entry of cleaning equipment. Not for personnel entry What is an inverted siphon used for and describe its basic construction? - correct answers An inverted siphon is used where a gravity wastewater line must go below the hydraulic gradient such as under a creek or drainage ditch. The line is split into two or preferably three smaller pipes. The goal is to speed the flow up to a minimum three fps.

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Internal inspection of the collection system can be accomplished by?

• correct answers a. television cameras b. lamping List four methods of cleaning wastewater lines. - correct answers a. manual rods b. rodding machines c. jet machines d. bucket machines e. balls, bags, and kites In-place repair of collection system piping can be made by? - correct answers a. internal grouting b. slip-lining c. pipe bursting What is the principle behind the use of bubbler tubes? - correct answers Differential pressure as caused by the water column Two pumps are in parallel pumping in a lift station (high head). What is the effect on the pumps? - correct answers One pump pumping alone will produce more output than it will when pumping in parallel with another pump. What is the effect on a centrifugal pump if the discharge valve is closed while the pump is running? - correct answers Power consumed will decrease resulting in lower amps being used.

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List the gases and their properties that are commonly encountered in wastewater collection systems. - correct answers a. Methane (CH4) - Lighter than air, explosive/flammable b. Hydrogen Sulfide (H2S) - Slightly heavier than air, flammable, corrosive, toxic, rotten- egg odor in lower concentrations c. Carbon Dioxide (CO2) - Much heavier than air, corrosive, non- toxic, non-flammable, displaces oxygen causing suffocation List the three cycles of decay and what is the desired end compound of each cycle - correct answers a. nitrogen - nitrate b. sulfur - sulfates c. carbon - carbohydrates pH meters should be calibrated how often? What standards should be used for calibration purposes? - correct answers Daily with at least two buffers and bracketing your sample. Usually 4.0 and 7.0 or 7.0 and 10.0. Three point is better utilizing 4.0, 7.0, and 10.0. List the three types of organic matter - correct answers a. carbohydrates b. proteins c. greases All organic matter contains what? - correct answers Carbon, oxygen, hydrogen Define pH technically - correct answers a. Logarithm of the reciprocal of the hydrogen ion concentration.

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b. Negative logarithm of the hydrogen ion concentration List the radicals that cause alkalinity and their pH range. - correct answers a. Bicarbonate HCO3 - below 8.3 pH b. Carbonate CO3 - 8.3 to 9.5 pH c. Hydroxide OH - 9.5+ pH What is gram equivalent weight and gram molecular weight? - correct answers a. Gram molecular weight - Molecular weight of a compound weighed out in grams. b. Gram equivalent weight - Molecular weight of a compound divided by the electrons transferred (valence) weighed out in grams. What is the percentage of BOD reduction if the raw influent has a BOD of 250 mg/L and the effluent from the primary clarifier is 160 mg/L? Is this reduction acceptable? - correct answers 250 - 160 = 90 ,g /L removed 90/250 = .36 *100 = 36% and yes How can dissolved oxygen (DO) measurements be analyzed? - correct answers a. DO meter b. Winkler-azide titration What is a 1N solution? - correct answers One gram equivalent weight of a compound made up to one liter (1000 mls) with distilled water

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What is the minimum acceptable velocity in any wastewater line? Why? - correct answers 2 fps to keep the solids moving and to scour the pipe A trench is 5,250 feet long, 4 feet wide, and 4 feet deep. There is a 12-inch diameter pipe laying in the bottom of the trench. How many cubic yards of dirt had to be hauled away from the job site? - correct answers 12/12 = 1 ft r =. 3.14 x 0.5^2 x 5250 = 4,121.25 ft^ 27 cubic ft per cubic yd 4,121.25 / 27 = 152.64 cu yd What is the standard chlorine residual and minimum contact time on Texas wastewater permits? - correct answers a. 1.0 mg/L for a minimum 20 minutes detention time at peak flow b. No chlorine residual needed if detention time is greater than 21 days List four methods for controlling levels in lift stations. - correct answers a. floats b. electrodes c. bubbler tubes d. ultrasonic What is the most common of type power used in wastewater plants and lift stations? - correct answers 440 - 480 volt three phase power is the most common used

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List the three general groups of bacteria by oxygen needs - correct answers a. aerobic - needs dissolved oxygen b. anaerobic - needs combined oxygen, does not utilize DO c. facultative - will utilize DO or combined oxygen Define pathogens and give several examples of waterborne pathogens. Identify them as bacteria, viruses, or protozoa. - correct answers Pathogens are disease causing organisms. (Bacteria) a. Typhoid b. Paratyphoid c. Bacillary Dysentery d. Cholera e. Campylobacterosis f. Legionaire's Disease (Virus) infectious Hepatitis (A) h. Poliomyelitis i. Gastroenteritis (mild and acute) (Protozoa) j. Amebic Dysentery k. Giardiasis (chlorine resistant) l. Cryptosporidiosis (chlorine resistant) What is the minimum DO level in the aeration chambers of a contact stabilization plant? - correct answers 2.0 mg/L Is BOD5 a good test for operating an activated sludge plant? Explain your answer. What would be a better test and why - correct answers No it is not. Results take a minimum of five days under the best condition. It tells us where a plant was, not where it is operating today. The COD test would be much better for operating as results can be had in two to four hours. What is the formula for calculating BOD? - correct answers DO before - DO after x 100 / % dilution

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Describe BOD. What does it stand for and what are the parameters of the test? - correct answers BOD - Biochemical Oxygen Demand five days at 20 degrees centigrade A 30 mL wastewater sample, 270 mL dilution water, DO before 8. mg/L, DO after 4.1 mg/L, what is the BOD? - correct answers DO before - DO after x 100 / % dilution 30 mL sample +270 mL dilution water = 300 mL Dilution= 30/300 = 0.10 = 10 % (8.0 -4.1)/.10 = 39 mg/L BOD What is a compound? Give some examples. - correct answers Two or more elements that combine to form a compound that is electrically neutral. The resulting compound does not resemble either of the parent elements. An example would be Sodium (Na) which is a metal and Chlorine (Cl) which is a toxic gas. Together they form (NaCl) which is salt. What is a radical and give three examples commonly found in wastewater? - correct answers A radical is two or more elements that are not electrically neutral, but act as if they were a single element. A good example would be hydroxide (OH), Bicarbonate (HCO3), and carbonate (CO3). How do you calculate the molecular weight of a chemical compound?

• correct answers The molecular weight of a compound is the sum of the atomic weights of the elements that make up the compound.

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How do you calculate the equivalent weight of a chemical compound? - correct answers The equivalent weight of the compound is the molecular weight divided by the valence or electrons transferred. You have one liter of a 1.5 N solution. You need 600mL of a 0.1N solution. How much of the 1.5 N solution do you use to make 600 mL to 0.1 N? - correct answers V1 x C1 = V2 X C 600 x .1 = V2 x 1. 600*.1 / 1.5 = v v2 = 40 mls How do you calculate the BOD population equivalent of an industrial discharge? - correct answers Population equivalent = lbs BOD discharged/ 0.17 lbs BOD/person What are the types of solids? - correct answers suspended organic settleable dissolved inorganic non-settleable What are some of the common tests performed on streams? - correct answers a. dissolved oxygen b. pH c. clarity d. conductivity As the complexity of an organization increases, what management function becomes most important? - correct answers Planning

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List and discuss the five steps in alignment of a pump and motor - correct answers a. Preparing the pump b. Preparing the motor c. Shaft preparation d. Preliminary alignment e. Determining the running clearance Describe the necessary safety procedures and equipment needed to work in trenches. - correct answers a. five feet or deeper utilize sloping, shielding or shoring b. four feet or deeper ladders extending three ft above trench, each worker within 25 ft of ladder c. dewatering pumps d. barricades, cones, flaggers, etc. e. PPE such as hardhats, gloves, safety classes, etc. Describe the necessary safety procedures and equipment needed to work in confined spaces - correct answers a. body harnesses, lifelines, tripods and winches b. Detection instruments for oxygen, flammability, and toxic gasses c. communication equipment d. permit entry program e. trained entrants, attendants, and rescuers f. PPE and rescue equipment such as SCBA's

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What is the GPM output of a piston pump with an 8-inch diameter piston with a 10-inch stroke operating at 50 strokes per minute? - correct answers 8/12 = 0.667 diameter r =. 10/12 = .833 lenght 3.14 * .333^2 x .833 x 7.48 x 50 = 108 gpm A given pump runs continuously and pumps 1.8 MGD. The pump efficiency is 77%, the motor efficiency is 75% and the friction loss is 6% of the total static head. The electrical costs are $0.115 per KWH. Assume the level in the wet well is 50 feet below pump discharge. What is motor horsepower required? Daily Operational cost and for one year. - correct answers a. What is the motor horsepower required? 1.8 mgd x 694.4 = 1250 gpm 50 x 1.06 = 53 ft of head (1250*53) / (3960 *.77 *.75) = 28.97 mhp What does it cost to operate the pump for 24 hours? 28.97 mph x 0.746 kwh/mhp x 24 hours x 0.115 = $59. 59.65 x 365 = $21,772. A pump with a 15-inch impeller is running at 1160RPM and is pumping 600 GPM with a 70 foot head. Pump is 80% efficient. If the RPM is increased to 1750 RPM, calculate the following: New GPM, New Head, New BHP - correct answers New GPM? 1750/1160 = 1.51 factor 600 x 1.51 = 906 gpm

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New Head 70 x 1.51 x1.51 = 159.6 ft head New BHP = (906 gpm x 159.6 ft head)/ (3960 x 0.80) = 45.6 BHP What is formed when chlorine gas combines with water? - correct answers Hypochlorous Acid (HOCl) + Hydrochloric Acid (HCl) What is the effective chlorine disinfecting agent? - correct answers Hypochlorous Acid (HOCl) Does pH affect the chlorination process? Explain your answer. - correct answers When using free chlorine the disinfectant is HOCl acid. As such it is much more effective at pH's below 7.0. Above 7. pH the acid begins to be neutralized. What is the effluent chlorine residual in Texas that is standard on permits and the minimum detention time? What is the maximum residual allowed? - correct answers Texas standard is 1.0 mg/L for a minimum 20 minutes detention time at peak flow. Maximum residual allowed is 4.0 mg/L. Describe the reaction between free chlorine and organics that might be in the water? - correct answers A free chlorine residual and natural organic material in the water (TOC's) form disinfection by- products know as Trihalomethanes (THM's) and Haloacetic Acids (HAA5's). These have been shown to cause cancer. Describe the different types of chlorine residuals. - correct answers Free Chlorine - must stronger, forms by-products, dissipates faster

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Chloramine - chlorine and ammonia, much weaker disinfectant, lasts longer, does not form THM's or HAA5's Define chlorine dosage, demand, and residual. - correct answers a. Dosage - what is put in b. Demand - what is used up c. Residual - what is left over List at least six uses of chlorine in wastewater treatment - correct answers a. disinfection b. odor control c. BOD reduction d. control ponding on trickling filters e. bulking f. clarifier settling List the types of primary treatment - correct answers a. screening b. primary clarifiers c. grit removal d. grease removal e. Imhoff tanks Primary treatment should remove ________% BOD, ___________% suspended solids, and _____________% settleable solids - correct answers 30-40% BOD 50-70% 90%

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List the various types of screening devices - correct answers a. bar screens b. drum screens c. disc screens d. barminuter/cominuter Velocity in a grit chamber should be? - correct answers 1.0 feet per second. How does a grit removal unit operate? - correct answers Velocity is lowered to 1.0 fps or less. The grit will fall out where it can be collected and disposed of A treatment plant has a daily flow of 4.5 MG. Eight thousand (8,000) gallons of sludge is pumped per MG treated. Two sludge pumps alternate pumping every two hours at a rate of 300 GPM. How long do the pumps run? - correct answers 4.5 x 8000 = 36,000 gal sludge 3600/12 = 3,000 gal/ 2 hr 3000 gal/300gpm = 10 minutes / 2 hr The normal flow into a treatment plant is 3.0 MGD and the peak flow is 9.0 MGD. What is the capacity of a clarifier necessary to give a 2- hour detention time? - correct answers 9,000,000/24 = 375,000 gph 375000 x 2 = 750, A treatment plant has a clarifier that is 60 feet in diameter and is 10 feet deep. The weir is 2 feet inside the outer clarifier wall. The flow is 1.0 MGD. The weir and outflow channel is 3 feet deep. What is the

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detention time in hours? What is the surface loading in gal/ft2 /day? What is the weir loading in gal/linear ft/day? - correct answers detention time in hours 3.14 x 30 x30 x 7 x 7.48 =147,969. 3.14 x 28 x 28 x 3 x 7.48 = 55,241. 147.969.36 + 55,241.8499 = 203,211. 1,000,000 / 24 = 41,677 gph 203,2121.21/41,677 = 4.9 hours surface loading in gal/ft2 /day 3.14 x 28 x 28 = 2,461.76 ft^ 1,000,000/2,461.76 = 406.21 gal/ft^2/day What is the weir loading in gal/linear ft/day? Weir length = 2 * π * (diameter/2 - weir distance from wall) Weir length = 2 * π * (60/2 - 2) Weir length ≈ 175.84 feet 1,000,000 / 175.84 = 5,687 gal/ft/day A primary clarifier has a flow of 3.0 MGD and has a diameter of 100 feet. It is 12 feet deep and has 24 inches of freeboard. What is the detention time in hours? - correct answers 3.14 * 50 *50 * (12 - 2) x 7.48 = 587,1802 gal ]3,000,000/24 = 125, 587,180 / 125,000 = 4.7 hours What factors influence settling in clarifiers? - correct answers a. detention time b. temperature c. wastewater condition (fresh or septic)

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d. velocity e. short circuiting Describe how an Imhoff tank operates and the necessary maintenance. - correct answers An Imhoff Tank is a primary clarifier over an anaerobic digester. It is primary treatment only. Maintenance includes cleaning the walls of the clarifier, chaining the slot or opening into the digester, keeping the gas vents clean and open, and drawing the sludge off when it gets to within 18 inches of the slot. List the three general types of sludge encountered in wastewater treatment. - correct answers a. primary or raw from primary clarifier b. activated from an activated sludge plant final clarifier c. Humus from the secondary clarifier in tricking filters and RBC's d. Treated or digested sludge List the stages in the order in which they occur in proper anaerobic digestion. - correct answers First stage - Acid Second stage- Acid regression Third stage - Alkaline The biological reduction of sulfate compounds in the absence of air results in - correct answers H2S. Anaerobic digester gas should contain ______% methane, _______% carbon dioxide and ________% nitrogen. - correct answers Anaerobic

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digester gas should contain 65-75% methane, 25-35% carbon dioxide and 1-5% nitrogen. Describe the 30 minute settleability test. What are the settling characteristics of a good quality sludge? - correct answers Mixed liquor is poured into a settleometer that is graduated from 0 to 1,000. The operator observes how the sludge settles over a 30 minute period recording the level every five minutes. If the MLSS is good it will settle gently and uniformly leaving a clear supernatant. Most of the settling will occur in the first 15 to 20 minutes. The settled level after 30 minutes should be 250 to 400 mls What activated process cannot nitrify in a single stage? - correct answers Contact Stabalization What are three methods of trench cave-in protection? - correct answers a. sloping to the angle of repose b. shielding/trench boxes c. shoring How is sludge volume index calculated? Describe what the index number means. - correct answers (30 min settled volume/ MLSS) x 1000 = SVI 70 -150 ok 710 -125 optimal The percent settled solids is 25% and the MLSS is 1,000 mg/L. What is the SVI? Describe your result. - correct answers (30 min settled volume/ MLSS) x 1000 = SVI (250/1000) * 1000 = 250 SVI

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Average daily flow of a treatment plant is 3.5 MGD. Influent TSS is 260 mg/L. Tank volume is 1.2 MG. MLSS is 3200 mg/L. What is the average age of the solids in the tank? - correct answers (Gould Sludge Age) = lbs TSS in aeration basin/ lbs TSS influent (1.2 x 3,200 x 8.34)/ ( 3.5 x 260 x 8.34) = 4.22 days Gould Sludge Age - correct answers lbs TSS in aeration basin/ lbs TSS influent An activated sludge plant has an average daily flow of 3.5 MG. The aeration tank capacity is 1.2 MG with a MLSS concentration of 3200 mg/L. The clarifier has a capacity of 400,000 gallons with a MLSS concentration of 6,000 mg/L. The wasting rate is 40,000 gallons per day with a MLSS concentration of 8, 000 mg/L. The effluent TSS is 18 mg/L. Assuming volatile concentrations of 70%, what is the MCRT and what type of activated sludge plant should this be? - correct answers lbs MLVSS aeration + lbs MLVSS clarifier = Days lbs MLVSS waster + lbs MLVSS effluent 1.2 x 8.34 x 3200 x 0.7 = 22,2418 lbs aeration 0.4 x 8.34 x 6,000 x 0.7 = 14,011 lbs clarifier 22,418 + 14,011 = 36,429 lbs MLVSS in plant 0.04 x 8.34 x 8000 x 0.7 = 1,868 lbs dishcharged 3.5 x 8.34 x 18 x.7 = 368 lbs dishcharged 1,868 + 368 = 2,236 lbs MLVSS eliminated

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36,429 / 2,236 = 16.29 days Influent BOD is 300 mg/L and the daily flow is 3.5 MGD. The aeration tank capacity is 1.2 MG, the MLSS is 3200 mg/L, and the MLVSS is 70%. What is the F/M ratio? - correct answers lbs influent BOD / lbs MLVSS in Aeration Basin (3.5 x 300 x 8.34) / (1.2 * 3200 *8.34 *0.7) = 0.39 F/M Ratio What are the operator controls on an activated sludge plant? - correct answers a. Return rates (RAS) b. Waste rates (WAS) c. DO levels d. food supply if flow equalization is available What are some of the causes of bulking sludge? What is the most common cause? - correct answers a. young sludge b. high F/M ratio c. nutrient deficiencies d. excessive hydraulic loading e. low RAS and WAS rates f. filamentous bacteria What are some of the causes of filaments in the aeration basin? - correct answers a. low DO b. low organic loading c. septic wastes

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d. nutrient deficiencies e. high sulfur content What causes rising sludge? - correct answers nitrification - de- nitrification

. Identify the parts of a trickling filter and describe its operation? - correct answers The parts of a trickling filter are the floor, under- drain, tank walls, media either rock or plastic, and the distribution system. Wastewater that has received primary clarification is slowly distributed evenly across the surface of the media. The microcritters (zoolgleal mass) that stabilize the organic material live on the media. As the wastewater trickles down through the media the BOD is consumed as food. A trickling filter does not filter anything, it is a biological growth bed. Efficiency is measured by per cent BOD reduction. What are the operational problems with a trickling filter? - correct answers a. ponding b. filter flies (psychoda) c. anaerobic conditions d. snails e. clogged nozzles How is the efficiency of a trickling filter measured? - correct answers Percent BOD removal What is the maximum BOD loading on an oxidation pond? What is the minimum design detention time to avoid having to disinfect? - correct answers a. 35 lbs BOD per day per acre

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b. 21 days + holding time requires no disinfection An oxidation pond is serving a population of 2000. 30 percent of the BOD is removed in primary treatment. How large does the pond need to be? - correct answers 2000 x 0.17 = 340 lbs 340 x 0.7 BOD remaining = 238 lbs BOD Pond can hold 35 lbs BOD / Day per acre 238/35 = 6.8 acres Good sludge quality will have a predominance of what organisms in the MLSS? - correct answers Ciliated protozoa A predominance of filamentous organisms in an activated plant is an indicator of what? - correct answers a. bulking sludge b. low DO c. high organic loading d. old sludge How many acres of oxidation ponds would be needed for a daily flow of 1.5 MGD with 30 days detention time? Average pond depth is 4 feet. - correct answers 1,500,000 x 30 = 45,000,000 gallons ft^2 * depth x 7.48 = 45,000,000 ft^2 = (45,000,000 / (4*7.48) =1,504,011 43,560 ft^2 for 1 acre 1,504,011/43,560 = 34.53 acres of pond

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What is the definition of peak flow? - correct answers Highest two hour average flow rate generally the two year 24 hour storm. When an RBC is operating correctly, how will the slime appear on the media? - correct answers Grey to brown 0.05 to 0.1 inches thick What are two common types of filamentous bacteria? - correct answers a. Thiothrix - sulfur bacteria b. Sphaerotilus - organic overload c. Type 1701 - low DO d. Nocardia - old sludge Dissolved Air Flotation is used in what treatment process? - correct answers Grease removal What is another name for contact stabilization? - correct answers Biosorption What activated sludge process does not achieve complete nitrification? - correct answers Contact Stabilization According to design criteria, what are the minimum allowable diameters for a manhole? - correct answers 24 inch opening and 48 inch inside diameter In the selection of forced main wastewater piping, what is the minimum working pressure? - correct answers 150 psi