Test 19 - Biochemical Oxygen Demand

Question 1 ప్రశ్న 1

What does biochemical oxygen demand (BOD) primarily indicate in wastewater engineering?

A The concentration of dissolved oxygen already present in the wastewater. B The oxygen needed to oxidize all dissolved and suspended substances by a strong chemical reagent. C The oxygen consumed by microorganisms in stabilizing biologically oxidizable substances under specified test conditions. D The total mass of microorganisms present, irrespective of their oxygen consumption.

Question 2 ప్రశ్న 2

Which pairing correctly distinguishes the commonly used Indian BOD incubation convention from the international five-day BOD convention?

A Indian BOD3: 3 days at 27°C; BOD5: 5 days at 20°C. B Indian BOD3: 3 days at 20°C; BOD5: 5 days at 27°C. C Indian BOD3: 5 days at 27°C; BOD5: 3 days at 20°C. D Indian BOD3: 1 day at 37°C; BOD5: 5 days at 37°C.

Question 3 ప్రశ్న 3

Why are BOD bottles kept in the dark during incubation?

A To prevent all bacterial respiration during the test. B To avoid photosynthetic oxygen production that can distort dissolved-oxygen depletion. C To promote atmospheric oxygen entry through the bottle stopper. D To ensure that all nitrogenous oxygen demand is chemically removed.

Question 4 ప్రశ్న 4

For a routine diluted BOD determination using the usual oxygen-depletion acceptability criteria, which bottle result is acceptable for calculation?

A DO depletion of 1.0 mg/L and final DO of 3.0 mg/L. B DO depletion of 3.0 mg/L and final DO of 0.5 mg/L. C DO depletion of 0.5 mg/L and final DO of 0.5 mg/L. D DO depletion of 3.0 mg/L and final DO of 2.0 mg/L.

Question 5 ప్రశ్న 5

An unseeded BOD bottle contains a diluted sample with a sample-volume fraction of 0.05. Its initial and final DO are 8.6 and 4.1 mg/L after the specified incubation. Assuming negligible blank demand, what is the BOD of the original sample?

A 22.5 mg/L B 45 mg/L C 90 mg/L D 180 mg/L

Question 6 ప్రశ్న 6

A seeded BOD dilution uses 10 mL of original sample in a final volume of 300 mL. Diluted-sample DO falls from 8.8 to 3.3 mg/L; seed-control DO depletion is 1.0 mg/L and the seed correction factor is 0.50. What is the seed-corrected BOD of the original sample?

A 150 mg/L B 165 mg/L C 50 mg/L D 180 mg/L

Question 7 ప్రశ్న 7

A diluted BOD test bottle begins with 8.0 mg/L dissolved oxygen and ends with 0.2 mg/L. What is the most appropriate interpretation under routine minimum-residual-DO requirements?

A The measured depletion is automatically the exact BOD because oxygen is nearly exhausted. B The bottle fails the residual-oxygen criterion and a more suitable dilution should be evaluated. C The result is invalid only if the initial DO was below 2.0 mg/L. D The sample necessarily contains no biodegradable organic matter.

Question 8 ప్రశ్న 8

An undiluted, unseeded surface-water sample with sufficient natural microorganisms has initial DO of 7.9 mg/L and final DO of 5.1 mg/L after the specified BOD incubation. What is its measured BOD?

A 13.0 mg/L B 5.1 mg/L C 7.9 mg/L D 2.8 mg/L

Question 9 ప్రశ్న 9

A wastewater has an expected BOD of 240 mg/L. For a 300 mL unseeded BOD bottle, which sample volume should theoretically yield about 4.0 mg/L DO depletion, assuming proportional response and negligible blank demand?

A 2 mL B 10 mL C 5 mL D 20 mL

Question 10 ప్రశ్న 10

A treatment plant receives 2.0 MLD of sewage having a BOD concentration of 200 mg/L. What is the incoming BOD mass load?

A 400 kg/day B 100 kg/day C 200 kg/day D 4,000 kg/day

Question 11 ప్రశ్న 11

A sewage-treatment unit lowers BOD from 250 mg/L to 40 mg/L. Assuming inlet and outlet concentrations are comparable under the same BOD test procedure, what is the percentage BOD concentration reduction?

A 75% B 84% C 16% D 90%

Question 12 ప్రశ్న 12

Two domestic wastewater samples are tested using identical BOD procedures without microbial inhibition. Sample X has BOD of 320 mg/L and sample Y has BOD of 80 mg/L. What is the most defensible conclusion?

A Sample X necessarily contains four times as many pathogenic microorganisms. B Sample Y requires more microbial oxygen demand per litre because its BOD is lower. C Sample X necessarily has four times the COD of Sample Y. D Sample X exhibits four times the measured biochemical oxygen demand per unit volume under the stated test.

Question 13 ప్రశ్న 13

What is the principal purpose of adding a suitable nitrification inhibitor when measuring carbonaceous BOD (CBOD)?

A To increase the oxygen consumed by ammonia-oxidising bacteria. B To oxidise all remaining organic matter chemically before incubation. C To suppress nitrogenous oxygen demand so that the measured uptake primarily reflects carbonaceous oxidation. D To replace the need for viable microorganisms in the BOD bottle.

Question 14 ప్రశ్న 14

A heavily polluted industrial wastewater gives unexpectedly low BOD although other evidence indicates a high organic load. Which explanation should be investigated first?

A Toxic substances or unsuitable pH may have inhibited the microorganisms used in the BOD bioassay. B A low BOD proves that the wastewater has no chemically oxidisable substances. C The oxygen demand of all industrial wastewater is necessarily lower than that of drinking water. D Industrial organic compounds always undergo complete biodegradation in three days.

Question 15 ప్రశ్న 15

For an ideal first-order carbonaceous BOD model using a natural-base deoxygenation constant k in day^-1, which expression gives BOD exerted by time t from ultimate demand L0?

A BODt = L0 exp(-kt) B BODt = L0[1 - exp(-kt)] C BODt = L0(1 + kt) D BODt = kL0/t

Question 16 ప్రశ్న 16

Wastewater has ultimate carbonaceous BOD L0 = 300 mg/L and a natural-base first-order deoxygenation constant k = 0.23 day^-1 at the specified temperature. What is the BOD exerted after five days?

A 95.0 mg/L B 300.0 mg/L C 109.8 mg/L D 205.0 mg/L

Question 17 ప్రశ్న 17

For a wastewater with ultimate carbonaceous BOD of 200 mg/L and natural-base k = 0.20 day^-1, how much oxygen demand remains unexerted after three days?

A 90.2 mg/L B 200.0 mg/L C 109.8 mg/L D 45.1 mg/L

Question 18 ప్రశ్న 18

In an ideal first-order BOD process, what fraction of ultimate BOD has been exerted when the elapsed time equals the half-life ln(2)/k?

A 50% B 25% C 75% D 100%

Question 19 ప్రశ్న 19

The measured five-day carbonaceous BOD is 180 mg/L at a specified temperature. If the natural-base first-order constant is k = 0.23 day^-1, what is the corresponding estimated ultimate carbonaceous BOD?

A 123.0 mg/L B 263.4 mg/L C 205.0 mg/L D 569.0 mg/L

Question 20 ప్రశ్న 20

For ideal first-order BOD exertion with natural-base k = 0.20 day^-1, approximately how much time is required to exert 75% of the ultimate BOD?

A 3.47 days B 5.00 days C 13.86 days D 6.93 days

Question 21 ప్రశ్న 21

At one fixed temperature, a wastewater follows first-order carbonaceous BOD kinetics with L0 = 250 mg/L and natural-base k = 0.20 day^-1. Which pair gives the approximate BOD exerted after 3 days and 5 days, respectively?

A 137.2 mg/L and 92.0 mg/L B 109.8 mg/L and 158.0 mg/L C 112.8 mg/L and 158.0 mg/L D 158.0 mg/L and 112.8 mg/L

Question 22 ప్రశ్న 22

In a first-order BOD model with natural-base k = 0.25 day^-1, the oxygen demand remaining at a particular instant is 120 mg/L. What is the instantaneous rate of BOD exertion at that instant?

A 30 mg/L per day B 480 mg/L per day C 120 mg/L per day D 0.0021 mg/L per day

Question 23 ప్రశ్న 23

Assume the empirical temperature relation kT = k20(1.047)^(T-20) for a natural-base BOD deoxygenation constant. If k20 = 0.20 day^-1, what is k30 approximately?

A 0.200 day^-1 B 0.317 day^-1 C 0.094 day^-1 D 0.470 day^-1

Question 24 ప్రశ్న 24

A report gives BOD3 measured at 27°C for one sample and BOD5 measured at 20°C for another. Which interpretation is technically valid?

A The reported values are necessarily equal whenever the ultimate BOD is equal. B BOD3 at 27°C is always numerically larger than BOD5 at 20°C, irrespective of sample kinetics. C BOD3 at 27°C can be directly converted to BOD5 at 20°C by multiplying by 5/3 for every wastewater. D The methods have different time-temperature conditions, so conversion or comparison requires appropriate sample-specific assumptions or evidence.

Question 25 ప్రశ్న 25

Two wastewater streams mix without reaction or loss: 2 MLD at BOD 200 mg/L and 3 MLD at BOD 100 mg/L. Assume comparable BOD tests and additive oxygen-demand loads. What is the mixed BOD concentration?

A 120 mg/L B 150 mg/L C 140 mg/L D 300 mg/L

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