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1 Serial : IG1_CE_A_Environmental Engineering_ CLASS TEST (GATE Delhi Noida Bhopal Hyderabad Jaipur Lucknow Indore Pune Bhubaneswar Kolkata Patna Web: info@madeeasy.in Ph: CLASS TEST CIVIL ENGINEERING Subject : Environmental Engineering Date of test : 10/08/018 Answer Key 1. (a 7. (a 1. (a 19. (c 5. (b. (b 8. (b 14. (d 0. (c 6. (d. (c 9. (c 15. (a 1. (a 7. (d 4. (a 10. (c 16. (b. (d 8. (c 5. (c 11. (d 17. (a. (c 9. (b 6. (c 1. (b 18. (c 4. (d 0. (a

2 CT-018 CE Environmental Engineering 7 Detailed Explanations 1. (a Velocity gradient, G P µ V Power input per unit volume, P µg V 1 10 ( W Now, power input per unit volume P V 50 W. (b 1 gm of aluminium produces 0.4 gm of Al(OH 16 mg/l of aluminium will produce Al(OH mg/l Dry sludge (suspended solids removed mg/l Total dry sludge mg/l 4. (a 750 Specific weight of MSW Volume of food, V 1 Volume of plastics, V Volume of dirt, V Volume of wood waste, V 4 where x is specific weight of wood waste Total Volume Total weight Volume m m m 0 10 m x x ( x x kg/m

3 8 Civil Engineering 5. (c The tolerance limit for BOD 5 in marine environment disposal is 100 mg/l. Minimum efficiency needed, η min % (c t Relative Stability, S ( t 7 days ( 7 t 7 7. (a SVI Settled sludge volume m /g MLSS 800 l 8. (b Overflow rate m /day/m m/day Percentage particle removal 1000 mm/s 0.55 mm/s % (c Let volume of raw sewage V Dilution ratio 00 V Loss of D.O. during 5 days incubation Initial D.O. FInal D.O mg/l BOD of sewage Loss of D.O. Dilution factor V V.5 ml 10. (c Head loss per unit length is independent of sewer running full or half full condition. 11. (d (i Lime (CaO required for alkalinity (CaCO Molecular weight of CaO Molecular weight of CaCO CaO required for 150 mg/l alkalinity mg/ l kg 84kg l 6 10 l

4 CT-018 CE Environmental Engineering 9 (ii Lime required for MgSO 4 Molecular weight of MgSO CaO required for 90 mg/l of MgSO kg 90 4mg/ l l Total lime required kg/10 6 l Total lime required to treat 10 6 litres of water 16 kg 1. (b Total water filtered in a day 1 ( m /day Total surface area of filter required 86400m /day 140m /day/m m Area of one filters required m Total number of filter As three filters are out of service, number of filters working 1 10 Total surface area of ten filters m New loading rate m /day 180 m /day/m 480 m 1. (a Year Total Population 5,000 8,000 4,000 4,000 47,000 Increase in Population Average increase in population per decade, x Average incremental increase, Incremental increase y ( P 00 P x+ y (d Flow rate of river, Q R 600 l/sec Concentration of sodium in river water, C R 17 mg/l Concentration of sodium in waste water channel, C W 50 mg/l

5 10 Civil Engineering Concentration of sodium in the mix water, C mix 50 mg/l Let, flow rate of waste waterq W Concentration of sodium after mixing of waste water with river is given by CQ R R + CWQW C mix QR + QW Qw QW 50 (600 + Q W Q W Q W Q W Q W Q W 99 l/sec Dilution ratio Total discharge after mixing Discharge of waste water QR + QW Q 99 W 15. (a Given: BOD 5 L 5 00 mg/l, t 5 days, k 0 0. per day BOD 5 BOD u ( 1 e k 0t k0t L 5 Lu ( 1 e Lu ( 1 e 00 L u e k T 0 k T 0 θ 9.67 mg/ l k 15 k 0 ( (θ is generally taken as k ( k per day k15t L 8 Lu ( 1 e L (1 e mg/l 5 mg/l 16. (b The cloth area required ( 0m /sec 60s/min 100m /min 40m 5.0m/min 5.0m/min The surface area of one bag πdh π m Total number of bag bags 10.05

6 CT-018 CE Environmental Engineering (a Efficiency of filter, η Y V F where, Y Total BOD applied to filter unit V Volume in hectare meter 165 m m ha.m F Recirculation factor F R 1+ I 0.1R 1+ I F ( Y Y kg/day 18. (c Initial oxygen deficit saturation D.O. Initial oxygen content mg/l f KR 0. K 0.1 D Critical time, t c 1 D0 log 1 ( f 1 f KD ( f 1 L 1 5 log 1 ( 1 0.1( t c.7875 days.788 days L f Critical deficit, D C [ 10] [ ] KD tc D C 6.1 mg/l 19. (c Sewage flow, Q 0. m /s m /d Suspended solid in the influent 50 mg/l Suspended solids in the effluent ( mg/l 0.1 kg/m Total suspended solids per day kg/m

7 1 Civil Engineering So, sludge production per day ( kg/d 66.9 tonnes/d (c Given, d D α 1 cos α D α 0.6 D d Now, q Q α sinα 60 π / α 60 5/ 0.67 q m /sec 1. (a (i Al (SO 4 18HO + Ca(HCO A l(oh + CaSO 4 + 6CO 666 gm ( 16 gm (ii CaCO + HO + CO Ca(HCO 100 gm 16 gm From (i it is clear that 666 gm filter alum can neutralize ( 16 gm of alkalinity as Ca(HCO. Again from (ii it is clear that this ( 16 gm alkalinity as Ca(HCO is equivalent to ( 100 gm of alkalinity as CaCO. Total alkalinity of filter alum as CaCO, for water requiring 5 mg/l of filter alum mg/l 666 Hence, total alkalinity requirement mg/day mg/day Hence, total alkalinity requirement will be mg per day as CaCO.. (d Sewage produced litres/day 5 day BOD of sewage 185 mg/litres BOD of effluent 5 mg/litres BOD removed by pond ( mg/litres Sewage solids removed per day kg It is given that organic loading 65 kg/ha/day

8 CT-018 CE Environmental Engineering 1 Required area ha ha. (c Flow rate, Q o 575 m /hour Influent BOD, S o 165 mg/litre Effluent BOD, S 1 mg/litre Hydraulic retention time 6 hours 1 4 day Mean-cell resistance time (θ c 88 hours 1 days Volume, V 6000 m Mixed liquor suspended solids, X 500 mg/l F M QS o o VX Aeration tank kg biomass per day per kg 0.15 kg biomass per day per kg Secondary clarifier Effluent Solids wasted Mean cell residence time, θ c Q w X u VX Q X w C u VX θ kg/day 4. (d Flow of waste water stream, Q w m /sec Ultimate BOD of waste water stream, Y w 95 mg/l 95 gm/m Flow of river, Q R 16 m /sec Ultimate BOD of river, Y R 4 mg/l 4 gm/m BOD of mixture, Y 0 QY w w + QY R R Qw + QR gm/m k D 0.44 k /day Area of river 60 m Combined flow of river (downstream m /sec Stream velocity Time taken, t Y t Discharge Area m / sec sec days kd Y t

9 14 Civil Engineering [ t ] [ ] mg/l 5. (b Particles with velocity above or equal to SOR will be completely removed and those with settling velocity V below SOR are removed in proportion to, where V is the settling velocity. SOR Thus overall removal ( mg/l 6. (d Carbonate hardness 10 gm equivalent (If Non-Carbonate Hardness is present, sodium alkalinity i.e. NaHCO will be absent. g as CaCO l 150 mg/l as CaCO Non-Carbonate hardness Total hardness Carbonate hardness Total hardness 6 50 mg/l as CaCO [Total hardness is due to Ca + and Mg + only] 00 mg/l or CaCO NCH mg/l as CaCO 7. (d Dry sludge content produced kg/day Now 97% moisture content means that kg of dry sludge will produce 100 kg of wet sludge 880 kg of dry sludge will produce 8. (c Volume of wet sludge kg/day Mass of sludge m /day Density of sludge If capacity of digester is V then % of volume V gets filled with fresh sludge. 100 V 94.1 V 17. m Increase in population per year Additional discharge required to reach design capacity m /d 500 Present average water consumption per head per day m Increase in water consumption each year m /day Number of years required to reach design capacity years 184.8

10 CT-018 CE Environmental Engineering (b Flow rate, Q m /hour Influent BOD, S 0 10 mg/l Effluent BOD, S 8 mg/l Hydraulic retention time 6 hours 1 day 4 Mean-cell residence time, (θ c hours days 1.5days 4 MLSS (X 500 mg/l Volume 5000 m F M QS 0 0 VX day 1 0. (a Eckenfelder equation for computing the BOD removed by the filter is given as Y t Y 0 [ ] n kd / Q e L...(i where, Y 0 BOD 5 of the influent entering the filter (in mg/l Y t BOD 5 of the effluent getting out of the filter (in mg/l k rate constant per day D depth of filter (in m n depends on flow characteristics and is an empirical value. Q L Hydraulic loading rate per unit area of filter in m /m /day Q A Given: Y mg/l; D 1.5 m; k 1.89 d 1 ; n Q L.688m /m /day π 0 4 Substituting these values in equation (i, we get Y t [ ] 0.6 Y t Y t mg/l e