Solution:- the values given in the question are as follows:
flow rate(Q)=44 L/s
BOD concentration in raw sewage=440 mg/L
BOD removed by primary sedimentation tank=30%
filter volume in first stage=826000 L
filter volume in second stage=2563000 L
recirculation rate(second tank)=0.5
(1)
the effluent concentration of BOD in primary tank=30% of BOD concentration in raw sewage
the effluent concentration of BOD in primary tank=(30/100)*440
the effluent concentration of BOD in primary tank=132 mg/L
the effluent concentration of BOD in secondary tank=BOD concentration in raw sewage-the effluent concentration of BOD in primary tank
the effluent concentration of BOD in secondary tank=440-132
the effluent concentration of BOD in secondary tank=308 mg/L
(2)
treatment efficiency of primary tank(p)=[volume filter by primary tank/total volume]*100
treatment efficiency of primary tank(p)=[826000/(826000+2563000)]*100
treatment efficiency of primary tank(p)=24.3729%
treatment efficiency of secondary tank(s)=[volume filter by secondary tank/total volume]*100
treatment efficiency of secondary tank(s)=[2563000/(826000+2563000)]*100
treatment efficiency of secondary tank(s)=75.627%
(3)
treatment efficiency of plant()=[total filtered volume/total volume]*100
where, total filtered water=volume filter by primary tank+volume filter by secondary tank
total filtered water=826000+2563000
total filtered water=3389000 L
total volume=volume filter by primary tank+volume filter by secondary tank+recirculation volume
total volume=826000+2563000+0.5*2563000
total volume=4670500 L
treatment efficiency of plant()=[3389000/4670500]*100
treatment efficiency of plant()=72.5618%
(4)
depth of each tank=5 m
let diameter of primary tank is D1 and secondary tank is D2
volue(V)=area of tank*depth of tank
volue of primary tank(V)=area of primary tank*depth of primary tank
primary tank filter volume=826000 L
where, 1000 L=1 m^3
826000*10^-3=(3.14159/4)*D1^2*5
D1^2=210.3391
D1=14.5030 m
diameter of primary tank(D1)=14.5030 m
volue of secondary tank(V)=area of secondary tank*depth of secondary tank
secondary tank filter volume=2563000 L, or 2563 m^3
2563000*10^-3=(3.14159/4)*D2^2*5
D2^2=652.66259
D2=25.54726 m
diameter of secondary tank(D2)=25.54726 m
[Ans]
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