Environmental Engineering (Part-5) (General Engineering) (SSC JE)

Total Questions: 54

31. The period of cleaning of a slow sand filter is usually [BPSC AE (GEN. ENGG.)-2006 ]

Correct Answer: (c) 1 month to 3 month
Solution:

Slow sand filters–
• Effective size of sand particles is taken to be 0.2 to 0.3 mm.
• Head maintained at the top of sand layer is equal to depth of sand layer.
• Coefficient of uniformity for filter medium should be 3 to 5.
• Design life of filters = 10 years
• Frequency of cleaning is 1-3 months
• During cleaning, top layer (1.5 to 3 cm) of sand is removed.
• Rate of filtration of this filter is 98-99%
• Slow sand filters should be used for small town/villages having population <5000
• These are not used for water having turbidity > 50 NTU.

32. The gas which may cause explosion in sewers is [BPSC AE (GEN. ENGG.)-2006 ]

Correct Answer: (b) Methane
Solution:

Decomposing waste materials in public and private sewer and septic systems create sewer gases.

• Methane is the largest single constituent of sewer gas, which includes an assortment of toxic and nontoxic gases. Such as hydrogen sulphide, carbon dioxide, ammonia, nitrogen oxides and sulphur oxide.

33. A bio-filter is an example of [BPSC AE (GEN. ENGG.)-2006 ]

Correct Answer: (d) high rate trickling filter
Solution:

A bio-filter is an example of high rate trickling filter. Bio-filter are an efficient solution for the removal of biodegradable components. The technique is mainly applicable at lower, stable concentrations and flow rates. It is a economical method both in terms of investment and operational cost.

34. Aerobic activity is maximum [BPSC AE (GEN. ENGG.)-2006 ]

Correct Answer: (a) in freshly produced sewage
Solution:

Aerobic activity is maximum in freshly produced sewage. Aerobic processes are characterized by high volumes of excess sludge and higher energy deamnds compared to anaerobic processes. Aerobic treatment allows fuly biological degradation of paper mill effluents.

35. Which of the following units is not used to measure turbidity of water? [BPSC AE (GEN. ENGG.)-29.03.2019 ]

Correct Answer: (b) ATU
Solution:

Turbidity–The turbidity is the measure of resistance to the passage of light through the water. The water is said to be turbid when it contains visible material in suspension. It is caused due to the presence of suspended and colloidal in the water.

The measurement of turbidity is done using the following– Turbidity rod– It is a field method
Jackson's turbdimeter– It is a laboratory method. Its unit is JTU.

• Baylis and Nephelometer turbidimeters are based on colour matching techniques and mostly used for domestic water supply.
• Acceptable limit is 1 NTU cause for rejection is 5 NTU (IS 10500:2012).

36. A sewer pipe contains 1 mm sand particles of specific gravity 2.65 and 5 mm organic particles of specific gravity 1.2, the minimum velocity required for removing the sewerage, is [BPSC AE (GEN. ENGG.)-29.03.2019 ]

Correct Answer: (d) 0.45 m/s
Solution:

37. If 2% solution of a sewage sample is incubated for 5 days at 20⁰C and depletion of oxygen was found to be 5 ppm, BOD of the sewage is [BPSC AE (GEN. ENGG.)-29.03.2019 ]

Correct Answer: (c) 250 ppm
Solution:

Given data,
Dilution factor (DF) = 2% = 2/100 = 0.02
Depletion oxygen (DO) = 5 ppm

38. The dimension of a rectangular settling tank is– length 24 m, width 6 m and depth 3 m. If 2-hour detention period for tank is recommended, the rate of flow of sewage per hour, is [BPSC AE (GEN. ENGG.)-29.03.2019 ]

Correct Answer: (d) 216 cu m
Solution:

39. In the determination of total dissolved solids, the water sample is dried at the temperature of [RRB S.S.E. (Secunderabad) 02.09.2015 (Shift-I) ]

Correct Answer: (c) 105 ± 5°C
Solution:

• This method is for the determination of total dissolved solids dried at 180ºC from drinking water.
• A well-mixed sample is filtered through a standard glass fiber filter, and the filtrate is evaporated to dryness in a weighed dish and dried to constant weight at 180ºC.

40. Bacteria in sewage are mostly: [RRB JE(Patna/Muzaffarpur/Chennai/Ahmedabad/Bangalore) 14.12.2014]

Correct Answer: (c) Saprophytic
Solution:

Saprophytic bacteria– Saprophytic or refuse eating bacteria obtain their nutrient from dead organic matter, exist independently of a living body and are generally harmless to living organisms, the saprophytic bacteria bring about the changes which reduce organic matter to harmless compounds, hence this class of bacteria is of the greatest aid and importance in the process of sewage purification.