Disposal of Sewage Effluents

Question 1
A city generates 40 \times 10^{6} kg of municipal solid waste (MSW) per year, out of which only 10% is recovered/recycled and the rest goes to landfill. The landfill has a single lift of 3 m height and is compacted to a density of 550 kg/m^{3}. If 80% of the landfill is assumed to be MSW, the landfill area (in m^{2}, up to one decimal place) required would be ______
A
25743.3
B
36548.4
C
27272.7
D
26845.6
GATE CE 2018 SET-1   Environmental Engineering
Question 1 Explanation: 
Total weight generated by city
=40\times 10^{6}\: kg/year
Weight of MSW going into landfill
=0.9\times 40\times 10^{6}\: kg/year
=36\times 10^{6}\: kg/year
Compacted density
=550\: kg/m^{3}
Compacted volume of MSW
=\frac{36\times 10^{6}\: kg/year}{550\: kg/m^{3}}
=65454.5454\: m^{3}/year
Total landfill volume = Vol. of MSD + Vol. of cover
Given, Volume of MSW =0.8\times Total landfill volume
\therefore Vol. of cover =0.2\times Total landfill volume
\therefore Total landfill volume =\frac{65454.5454}{0.8}m^{3}/year =81818.18175m^{3}/year
Height of landfill =3\: m
\therefore Area of lanfill=\frac{81818.18175}{3} =27272.7\: m^{2}/year
Question 2
The wastewater form a city, containing a high concentration of biodegradable organics, is beingsteadily discharged into a flowing river at a location S. If the rate of aeration of the river water islower than the rate of degradation of the organics, then the dissolved oxygen of the river water
A
is lowest at the locations S
B
is lowest at a point upstream of the location S
C
remains constant all along the length of the river
D
is lowest at a point downstream of the location S
GATE CE 2017 SET-1   Environmental Engineering
Question 2 Explanation: 



As given rate of aeration is less than rate of degradation which decreases with time/distance, minimum DO is observed downstream of point of disposal 'S' where both rate of a reaction and degradation becomes equals.
Question 3
In a certain situation, waste water discharged into a river mixer with the river water instantaneously and completely. Following is the data available :

Waste water:
DO = 2.00 mg/L
Discharge rate = 1.10 m^{3}/s

River water:
DO = 8.3 mg/L
Flow rate = 8.70 m^{3}/s
Temperature = 20^{\circ}C

Initial amount of DO in the mixture of waste and river shall be
A
5.3 mg/L
B
6.5 mg/L
C
7.6 mg/L
D
8.4 mg/L
GATE CE 2005   Environmental Engineering
Question 3 Explanation: 
\begin{aligned} DO_{mix} &=\frac{Q_{W}DO_{W}+Q_{R}DO_{R}}{Q_{W}+Q_{R}} \\ &=\frac{\left ( 1.10\times 2.00 \right )+\left ( 8.70\times 8.3 \right )}{1.10+8.70} \\ &=7.6\: mg/L \end{aligned}
Question 4
Match Group-I (Characteristics of sewage discharged into inland waters ) with Group-II (Allowable limit, mg/L).
A
P-2 Q-5 R-4 S-2
B
P-4 Q-1 R-6 S-4
C
P-3 Q-1 R-4 S-2
D
P-2 Q-1 R-6 S-3
GATE CE 2003   Environmental Engineering
Question 4 Explanation: 


There are 4 questions to complete.

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