Test 31 - Integrated Sewage Treatment Process Design

Question 1 ప్రశ్న 1

A municipal plant must remove coarse debris, abrasive grit, settleable solids and biodegradable organics, and must disinfect clarified effluent before discharge. Which liquid-treatment sequence is most appropriate for a conventional activated-sludge scheme?

A Screening, primary settling, grit removal, secondary clarification, aeration and disinfection. B Grit removal, screening, aeration, primary settling, disinfection and secondary clarification. C Screening, grit removal, primary settling, aeration, secondary clarification and disinfection. D Screening, grit removal, secondary clarification, primary settling, aeration and disinfection.

Question 2 ప్రశ్న 2

A wastewater plant has repeated pump impeller damage from rags and sand, although its biological reactor removes soluble BOD satisfactorily. Which process-train improvement should receive first priority?

A Restore effective screening and grit removal upstream of vulnerable pumps and downstream treatment units. B Increase aeration-tank MLSS to help biological flocs entrap coarse inert solids that have already passed the inlet pumps. C Increase primary-sludge withdrawal so heavy grit settles downstream of vulnerable raw-sewage pumps. D Use abrasion-resistant pump components alone and leave preliminary solids separation unchanged.

Question 3 ప్రశ్న 3

A screened and degritted municipal wastewater stream has relatively low settleable TSS but high soluble biodegradable BOD. If the objective is substantial soluble-BOD removal, which selection is technically justified?

A Use a larger primary clarifier as the sole main treatment because dissolved BOD follows the settled sludge. B Increase detention in primary settling and assume dissolved organics will adsorb sufficiently onto settling particles. C Use only a sludge thickener because its overflow will contain less soluble BOD. D Provide an appropriately designed biological treatment stage followed by suitable biomass separation.

Question 4 ప్రశ్న 4

At an activated-sludge plant, soluble BOD leaving aeration is low, but final-effluent TSS rises and the secondary-clarifier sludge blanket is increasing. What should the engineer investigate first?

A Increase the primary-clarifier detention time without examining the secondary sludge inventory. B Examine secondary-clarifier solids loading and settling, together with RAS and WAS operation. C Add a tertiary filter without first evaluating secondary sludge settling, blanket depth and withdrawal. D Raise aeration-tank organic loading because soluble BOD is already adequately removed.

Question 5 ప్రశ్న 5

A small municipality has biodegradable sewage, adequate site area, limited capacity for continuous aerator maintenance, and a requirement for conventional secondary BOD removal. Which treatment concept merits serious consideration in a comparative feasibility study?

A A primary clarifier alone, because settleable-solids removal guarantees secondary effluent quality. B An activated-sludge aeration tank without secondary settling or biomass return. C A properly loaded trickling filter with suitable distribution, ventilation and downstream secondary clarification. D An uncovered sludge digester connected directly to the final effluent outfall.

Question 6 ప్రశ్న 6

A conventional plant generates primary sludge and excess waste activated sludge while its final liquid effluent passes through disinfection. Which solids-handling arrangement is most defensible where anaerobic digestion has been selected?

A Return primary sludge to the aeration tank as if it were RAS and dewater WAS without checking its required stabilization. B Dilute the combined raw-sludge feed using clarified effluent before direct disposal, rather than providing the selected stabilization process. C Send primary sludge to final disposal after settling, and digest only secondary effluent solids that escape the clarifier. D Provide appropriate collection and thickening of primary sludge and WAS, then controlled digestion and subsequent dewatering or further handling.

Question 7 ప్రశ్న 7

A conventional carbon-removal activated-sludge plant must now meet a stringent ammonia-nitrogen limit, while no total-nitrogen limit is specified. Which integrated design review is most relevant?

A Check nitrification-capable aeration, oxygen supply, suitable biomass retention and secondary-solids handling. B Increase only primary settling time because dissolved ammonia is readily removed with primary sludge. C Replace secondary clarification with screening because nitrifying biomass cannot settle. D Increase air supply alone without verifying sludge age, nitrifier retention or secondary clarification.

Question 8 ప్రశ్న 8

A remote institutional site is considering a septic tank, but soil tests indicate low infiltration capacity and the groundwater table is seasonally close to ground level. Which integrated treatment and effluent-disposal decision is preferable?

A Use a deeper conventional soak pit without checking groundwater separation because the septic effluent is fully treated. B Evaluate site-appropriate further treatment and an approved disposal or conveyance route instead of assuming ordinary subsurface soakage is feasible. C Remove the septic-tank outlet tee so that solids improve the infiltration rate of the soil. D Increase septic detention time alone while leaving the site-dependent soil-absorption arrangement unverified.

Question 9 ప్రశ్న 9

A municipal works receives an unusually large load of sand and road grit following sewer cleaning, and its primary sludge hoppers are filling with heavy inert solids. Which process change most directly addresses the source of the problem?

A Improve upstream grit removal and grit handling while verifying preliminary hydraulic performance. B Increase WAS pumping because biological sludge production is responsible for mineral sand accumulation. C Install a larger disinfection contact tank to settle mineral particles after biological treatment. D Increase primary-clarifier scraper speed and underflow pumping without correcting upstream grit interception.

Question 10 ప్రశ్న 10

Digester supernatant is returned intermittently to the head of an activated-sludge plant, and each return coincides with an ammonia spike at the biological inlet. What integrated response should be evaluated?

A Ignore the return stream because sludge digestion completely eliminates soluble nitrogen. B Route all supernatant directly to the final effluent outfall without determining its characteristics. C Measure the sidestream nitrogen and organic loads, control or equalize the returns, and assess biological-treatment or sidestream-treatment capacity. D Enlarge the primary clarifier to remove dissolved ammonium from the sidestream before aeration.

Question 11 ప్రశ్న 11

Which interpretation of internal recycle streams is correct when comparing conventional activated sludge and a conventional trickling-filter process?

A In activated sludge, clarified effluent is returned to maintain biomass; in trickling filters, concentrated secondary sludge is always returned to the media. B Both processes routinely return concentrated secondary sludge to maintain suspended biological solids in their reactors. C In trickling filters, recirculation primarily maintains a suspended-growth MLSS inventory through a RAS line. D Activated sludge returns concentrated settled biomass to aeration, whereas trickling-filter recirculation generally reapplies liquid to the attached-growth bed.

Question 12 ప్రశ్న 12

A plant already meets its approved BOD and TSS discharge targets after secondary clarification but fails a specified microbial-quality target for a planned reuse application. Which modification should be considered first?

A Increase grit removal detention because this reliably inactivates microorganisms in the final effluent. B Provide an appropriate validated disinfection barrier, with any required upstream polishing, and verify the actual reuse-quality requirements. C Add a second secondary clarifier without evaluating whether microbial disinfection is required. D Replace biological treatment with primary clarification because it provides complete pathogen removal.

Question 13 ప్రశ్న 13

Raw sewage contains 250 mg/L BOD5 at 12 MLD. Primary clarification removes 30% of incoming BOD5, and the subsequent biological stage plus its secondary clarifier removes 85% of the BOD5 remaining after primary clarification. Assuming unchanged net liquid flow, what are the final BOD5 concentration and overall removal?

A 26.25 mg/L and 89.5% overall removal. B 37.5 mg/L and 85.0% overall removal. C 175 mg/L and 30.0% overall removal. D 17.5 mg/L and 93.0% overall removal.

Question 14 ప్రశ్న 14

A hypothetical plant treats 8 MLD containing 300 mg/L influent TSS. Primary settling captures 60% of this TSS, and a downstream polishing/settling stage captures 80% of the remaining TSS; assume no additional solids generation and unchanged net flow. What are final TSS and the solids mass captured in the downstream stage?

A 24 mg/L and 2,208 kg/day captured in the downstream stage. B 60 mg/L and 768 kg/day captured in the downstream stage. C 24 mg/L and 960 kg/day captured in the downstream stage. D 24 mg/L and 768 kg/day captured in the downstream stage.

Question 15 ప్రశ్న 15

An ASP receives 6.0 MLD of fresh primary effluent and operates at RAS ratio Qr/Q = 0.50. Its secondary clarifier removes 0.12 MLD as WAS in addition to RAS. Neglect all other liquid losses and additions. What are clarifier inlet flow and net clarified effluent flow?

A 6.0 MLD and 5.88 MLD, respectively. B 9.0 MLD and 5.88 MLD, respectively. C 9.0 MLD and 9.00 MLD, respectively. D 6.0 MLD and 6.12 MLD, respectively.

Question 16 ప్రశ్న 16

A primary clarifier ahead of biological treatment receives 10 MLD average flow and 24 MLD peak flow. For this design exercise, the specified maximum average and peak overflow rates are 40 and 80 m3/(m2 day), respectively. Which minimum effective plan area satisfies both limits?

A 250 m2, controlled by average-flow overflow rate. B 240 m2, obtained using a peak overflow rate of 100 m3/(m2 day). C 300 m2, controlled by peak-flow overflow rate. D 550 m2, obtained by adding the average and peak area requirements.

Question 17 ప్రశ్న 17

A conventional ASP receives 5 MLD of sewage at 240 mg/L BOD5, after primary settling removes 25% of the raw BOD5 load. If the selected aeration F/M is 0.25 kg BOD5/(kg MLVSS day) with MLVSS = 3.0 kg/m3, what aeration volume and fresh-flow nominal HRT result?

A 1,200 m3 and 5.76 hours. B 1,600 m3 and 7.68 hours. C 1,200 m3 and 7.20 hours. D 900 m3 and 4.32 hours.

Question 18 ప్రశ్న 18

A plant sends 1,200 kg/day of primary sludge dry solids at 65% volatile content and 600 kg/day of WAS dry solids at 75% volatile content to a digester. The blended thickened feed is 45 m3/day, the maximum specified VS loading is 1.5 kg/(m3 day), and minimum specified HRT is 20 days. What minimum effective digester volume meets both requirements?

A 820 m3, controlled by volatile-solids loading. B 820 m3, controlled by hydraulic detention. C 1,720 m3, obtained by adding both separately calculated volumes. D 900 m3, controlled by the minimum detention time.

Question 19 ప్రశ్న 19

Raw sewage BOD5 is 280 mg/L. Primary settling removes 25% of it and the final effluent from subsequent biological treatment and clarification is 42 mg/L at unchanged net flow. What are removal across the biological/secondary stage and overall removal from raw sewage, respectively?

A 85% and 80%. B 80% and 85%. C 75% and 85%. D 80% and 80%.

Question 20 ప్రశ్న 20

A sludge train blends 60 m3/day of WAS at 0.8% total solids by mass with 20 m3/day of primary sludge at 3.0% total solids by mass. A thickener captures 90% of the combined dry solids in an underflow at 4.0% total solids by mass. Assuming all wet-sludge densities are 1,000 kg/m3, what is the underflow volume?

A 27.0 m3/day. B 21.6 m3/day. C 24.3 m3/day. D 80.0 m3/day.

Question 21 ప్రశ్న 21

A combined-sewer catchment sends short-duration wet-weather surges to an STP that performs well in dry weather but experiences primary and secondary clarifier solids washout during peaks. Which integrated design response is most appropriate?

A Increase only the aeration-tank F/M ratio because clarifier hydraulic capacity is unrelated to incoming flow. B Bypass all preliminary treatment during storms so grit can settle in the secondary clarifier. C Raise WAS withdrawal without evaluating clarifier overflow, inlet hydraulics or permitted stormwater management. D Assess wet-weather flow management or equalization and verify peak hydraulic capacity and solids retention across the entire treatment train.

Question 22 ప్రశ్న 22

A trickling filter receives 3.0 MLD of primary effluent at 180 mg/L BOD5 and recirculates clarified liquid at a ratio of 1.0 to fresh flow. Its media area is 1,000 m2 and depth is 2.0 m. What are total applied hydraulic loading and external organic loading based only on fresh BOD5 mass?

A 6.0 m3/(m2 day) and 0.27 kg BOD5/(m3 day). B 3.0 m3/(m2 day) and 0.54 kg BOD5/(m3 day). C 6.0 m3/(m2 day) and 0.54 kg BOD5/(m3 day). D 3.0 m3/(m2 day) and 0.27 kg BOD5/(m3 day).

Question 23 ప్రశ్న 23

A proposed nitrifying ASP needs 600 kg O2/day for its specified carbonaceous treatment duty and must additionally oxidize 50 kg/day of ammonia nitrogen. Using a theoretical nitrification requirement of 4.56 kg O2 per kg ammonia nitrogen oxidized, what combined theoretical oxygen demand should be considered before field transfer corrections?

A 600 kg O2/day. B 828 kg O2/day. C 650 kg O2/day. D 2,880 kg O2/day.

Question 24 ప్రశ్న 24

An industrial cleaning stream periodically enters a municipal sewer, causing abrupt soluble-BOD loading and oxygen depletion in an activated-sludge reactor despite normal preliminary solids removal. Which intervention addresses the treatment train most effectively?

A Increase grit-chamber detention as the primary correction because soluble organics can settle with mineral grit. B Stop RAS pumping to reduce the oxygen uptake associated with the sudden loading. C Investigate source pretreatment and equalization, characterize the shock load, and reassess aeration and biological operating capacity. D Increase primary-sludge withdrawal as the only response to soluble organics that pass primary settling.

Question 25 ప్రశ్న 25

A land-constrained municipality has reliable skilled operation and must meet stringent carbon, ammonia and total-nitrogen targets together with an approved disinfection target. Which preliminary process-selection concept is most defensible?

A Evaluate compact biological nutrient-removal configurations with appropriate clarification or solids separation, polishing/disinfection where needed, and a complete sludge-handling line. B Use conventional carbon-removal activated sludge followed by disinfection and assume primary settling provides the nitrogen removal. C Use a standard high-rate trickling filter and secondary clarifier alone, assuming carbon removal also achieves the required total-nitrogen limit. D Use nitrifying activated sludge followed by disinfection and assume ammonia oxidation alone meets the total-nitrogen limit.

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