## Detention time

The digester volume is therefore:

Check SRT from the equation:

This is in excess of the recommended SRT of 15 days to ensure the growth of methane formers.

(b) The sludge yield from the process is: AXv=aS-bXvt

= (0.14)(9450)-(0.02)(5000)(3.6)=963 mg/L AXv=963 mg/Lx180 m3/day =173.34 kg/day(381.35 lb/day)

(c) Gas production: G=0.351(S-1.42AXv), where G=m3 of CH4 produced/day

G=0.351[(9.450)(180)-(1.42)(173.34)] =0.351(1701-246.14)=511m3 CH4/day or

G=5.62(Sr-1.42AXv), where G=ft3 of CH4 produced/day

G=5.62[(9450)(0.0476 MG/day)(8.34)-(1.42)(381.35)] =18,040 ft3/day (511m3/day)

Gas production can be also determined by using the approximate estimation, which is 1 kg CODelim yields about 0.3-0.5 m3 of methane. Therefore, total gas production: G=9.45 kg C0D/m3x180 m3 CH4/kg COD =510m3 CH4/day

(d) Heat required can be estimated by calculating the energy required to raise the influent wastewater temperature to 35°C (95°F) and allowing 1°F (0.56°C) heat loss per day of detention time. Average wastewater temperature=24°C (75.2°F) and heat transfer efficiency=50%.

x (specific heal)

x (specific heal)

_ (47,600 gal/day>(8.341b/galX95°F+ STF - 7\$.TF) 