30 real Environmental Engineering questions from the Civil Core bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is Biochemical oxygen demand?
Junior
A.bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity
B.dosing chlorine until all ammonia is oxidised and free residual chlorine begins to appear, marking the dose that gives true disinfection
C.oxygen consumed by microbes oxidising biodegradable organics, measured over 5 days at 20 °C or 3 days at 27 °C in Indian practice
D.oxygen equivalent of organics oxidised by potassium dichromate in a 2 to 3 hour test, always at least equal to the biological demand
2. Which term means: "oxygen consumed by microbes oxidising biodegradable organics, measured over 5 days at 20 °C or 3 days at 27 °C in Indian practice"?
A.Biochemical oxygen demand — dosing chlorine until all ammonia is oxidised and free residual chlorine begins to appear, marking the dose that gives true disinfection
B.Biochemical oxygen demand — stabilisation of sludge by bacteria without oxygen at about 35 °C for around 30 days, yielding biogas that is 65 to 70 percent methane
C.Biochemical oxygen demand — flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing
D.Biochemical oxygen demand — oxygen consumed by microbes oxidising biodegradable organics, measured over 5 days at 20 °C or 3 days at 27 °C in Indian practice
5. Which term means: "oxygen equivalent of organics oxidised by potassium dichromate in a 2 to 3 hour test, always at least equal to the biological demand"?
A.Chemical oxygen demand — pH 6.5 to 8.5, turbidity 1 NTU acceptable and 5 permissible, TDS 500 acceptable and 2000 permissible, residual chlorine at least 0.2 mg/L
B.Chemical oxygen demand — flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing
C.Chemical oxygen demand — millilitres occupied by one gram of activated sludge after settling 30 minutes; 50 to 150 settles well and above 150 indicates bulking
D.Chemical oxygen demand — oxygen equivalent of organics oxidised by potassium dichromate in a 2 to 3 hour test, always at least equal to the biological demand
8. Which term means: "calcium and magnesium salts; carbonate hardness is removed by boiling while non-carbonate hardness needs lime-soda or ion exchange"?
A.Hardness of water — pH 6.5 to 8.5, turbidity 1 NTU acceptable and 5 permissible, TDS 500 acceptable and 2000 permissible, residual chlorine at least 0.2 mg/L
B.Hardness of water — calcium and magnesium salts; carbonate hardness is removed by boiling while non-carbonate hardness needs lime-soda or ion exchange
C.Hardness of water — millilitres occupied by one gram of activated sludge after settling 30 minutes; 50 to 150 settles well and above 150 indicates bulking
D.Hardness of water — bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity
11. Which term means: "pH 6.5 to 8.5, turbidity 1 NTU acceptable and 5 permissible, TDS 500 acceptable and 2000 permissible, residual chlorine at least 0.2 mg/L"?
A.IS 10500 drinking water limits — pH 6.5 to 8.5, turbidity 1 NTU acceptable and 5 permissible, TDS 500 acceptable and 2000 permissible, residual chlorine at least 0.2 mg/L
B.IS 10500 drinking water limits — flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing
C.IS 10500 drinking water limits — bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity
D.IS 10500 drinking water limits — 24-hour standards of 60 µg/m³ for PM2.5 and 100 µg/m³ for PM10, with annual limits of 40 and 60 respectively
A.NAAQS particulate limits — flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing
B.NAAQS particulate limits — oxygen equivalent of organics oxidised by potassium dichromate in a 2 to 3 hour test, always at least equal to the biological demand
C.NAAQS particulate limits — millilitres occupied by one gram of activated sludge after settling 30 minutes; 50 to 150 settles well and above 150 indicates bulking
D.NAAQS particulate limits — 24-hour standards of 60 µg/m³ for PM2.5 and 100 µg/m³ for PM10, with annual limits of 40 and 60 respectively
17. Which term means: "bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity"?
A.Jar test — calcium and magnesium salts; carbonate hardness is removed by boiling while non-carbonate hardness needs lime-soda or ion exchange
B.Jar test — bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity
C.Jar test — stabilisation of sludge by bacteria without oxygen at about 35 °C for around 30 days, yielding biogas that is 65 to 70 percent methane
D.Jar test — 24-hour standards of 60 µg/m³ for PM2.5 and 100 µg/m³ for PM10, with annual limits of 40 and 60 respectively
20. Which term means: "dosing chlorine until all ammonia is oxidised and free residual chlorine begins to appear, marking the dose that gives true disinfection"?
A.Breakpoint chlorination — oxygen equivalent of organics oxidised by potassium dichromate in a 2 to 3 hour test, always at least equal to the biological demand
B.Breakpoint chlorination — dosing chlorine until all ammonia is oxidised and free residual chlorine begins to appear, marking the dose that gives true disinfection
C.Breakpoint chlorination — flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing
D.Breakpoint chlorination — pH 6.5 to 8.5, turbidity 1 NTU acceptable and 5 permissible, TDS 500 acceptable and 2000 permissible, residual chlorine at least 0.2 mg/L
23. Which term means: "millilitres occupied by one gram of activated sludge after settling 30 minutes; 50 to 150 settles well and above 150 indicates bulking"?
A.Sludge volume index — pH 6.5 to 8.5, turbidity 1 NTU acceptable and 5 permissible, TDS 500 acceptable and 2000 permissible, residual chlorine at least 0.2 mg/L
B.Sludge volume index — calcium and magnesium salts; carbonate hardness is removed by boiling while non-carbonate hardness needs lime-soda or ion exchange
C.Sludge volume index — stabilisation of sludge by bacteria without oxygen at about 35 °C for around 30 days, yielding biogas that is 65 to 70 percent methane
D.Sludge volume index — millilitres occupied by one gram of activated sludge after settling 30 minutes; 50 to 150 settles well and above 150 indicates bulking
26. Which term means: "flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing"?
A.Surface overflow rate — calcium and magnesium salts; carbonate hardness is removed by boiling while non-carbonate hardness needs lime-soda or ion exchange
B.Surface overflow rate — stabilisation of sludge by bacteria without oxygen at about 35 °C for around 30 days, yielding biogas that is 65 to 70 percent methane
C.Surface overflow rate — flow divided by tank plan area, the settling velocity that a particle must exceed to be removed, so it governs sedimentation tank sizing
D.Surface overflow rate — bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity
29. Which term means: "stabilisation of sludge by bacteria without oxygen at about 35 °C for around 30 days, yielding biogas that is 65 to 70 percent methane"?
A.Anaerobic sludge digestion — calcium and magnesium salts; carbonate hardness is removed by boiling while non-carbonate hardness needs lime-soda or ion exchange
B.Anaerobic sludge digestion — bench-scale trial dosing alum into water samples at varying doses to find the coagulant dose giving the best floc and lowest residual turbidity
C.Anaerobic sludge digestion — millilitres occupied by one gram of activated sludge after settling 30 minutes; 50 to 150 settles well and above 150 indicates bulking
D.Anaerobic sludge digestion — stabilisation of sludge by bacteria without oxygen at about 35 °C for around 30 days, yielding biogas that is 65 to 70 percent methane
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