## Solution

The load to the plant is increased to 225 m3/day (59,400 gal/day).

(a) Anaerobic process. New effluent concentration; from example 3: SRTmin=15 days; T= 35°C; a=0.14; b=0.02; ¿'=0.0005 L/(mg-day); Xv=5000 mg/L; CODR=10,500 mg/L; and volume=648 m3 (0.1712 MG). The new detention time is:

The COD effluent from the anaerobic process can be estimated by: The COD removed is: CODremoved=CODR-CODE = 10,500-1273 =9227 mg/L

Check SRT using the equation: New gas production. The sludge yield is:

AX^aCODremoved-bXvOQ '

= (0.14x9227-0.02x5000x2.9) mg/Lx59,400 (lb/MG)/mg/L

The mass of COD removed per day is:

Sr=CODremovedx Q

=9227 mg/Lx59,400 gal/dayx8.34x10-6 =4571 lb/day (2076 kg/day)

gal/day x8.34x10-

5r=9227 mg/Lx225 m3/dayx10-3=2076 kg/day

The methane production can be estimated from: G=5.62(Sr-1.42AXv)

where G is given in ft3 of CH4/day G=5.62(4571-1.42x496.4) =21,727 ft3/day (615 m3/day)

(b) Aerobic process. The new detention time is: The new COD removed:

From the equation:

By rearrangement, the new MLVSS are obtained as 