Problem

The two-stage anaerobic digesters at a trickling-filter plant are a fixed-cover lank for f...

The two-stage anaerobic digesters at a trickling-filter plant are a fixed-cover lank for first- stage high rale sludge stabilization with a liquid volume of 42,000 ft3 and a floating-cover second-stage storage and thickening tank with a volume of 70,000 ft3 between the lowered and fully raised cover positions. The quantity of raw sludge Applied is 2800 ft3/day contain­ing 5.0% solids that are 70% volatile,

(a) If 60% of the volatile solids in the raw sludge is reduced by digestion, calculate the solids concentration in the digested sludge leaving the first-stage digester,


 (b) Estimate the daily methane production in first-stage digestion, ,


 (c) If the digested, thickened sludge contains 7.0% solids, compute the maximum number of days of digested-sludge storage available, ,


(d) Assume the first-stage digester has been operated at a digesting sludge temperature of 35°C for several weeks. How would the gas production change if the operating temperature were decreased slowly to 25°C? How would gas production be affected by a slow increase in operating temperature from 35° to 45°C?

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