8.0sludge holding tank8.1Design Criteriaa)Sludge accumulation rate= 0.5 kg solid / kg BOD 1% with conc. transfer sludge b)Anaerobic storage capacity = 30 days8.2Volume Requirement DeterminationQa = 28.125 m3 / day BOD removed = (250 - 10) mg / L = [240 mg / L] [1kg / (106)mg ] [1000L/ 1m3 ] = 0.24 kg BOD / m3a) Daily BOD removed = Qa BOD removed = 28.125 m3 / day (0.24 kg BOD / m3) = 6.75 kg BOD / dayc) Assume, VSS in wasted sludge = 70% (* Ref. Env. Enginner H/book - vol 1 )VSS digested for a month storage =65%therefore, digested VSS volume=Total sludge accumulated 70% 65%=[3.375 kg solid / day] 70% 65%=1.536 kg/ dayTotal SS remained in sludge holding tank= [3.375 kg / day] - [ 1.536 kg / day]= 1.839 kg/ dayd) Specific gravity of digested sludge =1.015Water Density =1000 kg / m3Dry solid content =1%therefore, daily volume of sludge=[1.839 kg / day] / [1.015 (1000kg/m3 ) 0.01]=0.181 m3 / daye)Sludge volume for 1 month storage=0.181 m3 / day 30=5.473 m38.3 Provided Tank Capacitya) Tank diameter =3.0 mb) Water depth=2.6 mc) Effective cross section area =6.51 m2d) Effective endcap volume=1.23 m3 e) No of endcap=1f) Cylinderical tank length=1.0 m g) No of tank =1h) Volume of tank provided=(Cylinderica volume) + (endcap volume) =(6.51 m2 1 m) + 1.23 m3=7.74 m3 > 5.437 m3 (OK) i) Actual HRT=7.74 ( 30 / 5.437 )=42.7 days