# 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.