Effect of hydrolysis of municipal sludge on biogas production in the digestion process

One method of increasing the degree of fermentation and biogas production from sludge is to use two stage digestion, with prior hydrolysis. The main purpose of this study was to find the effect of separation of hydrolysis phase on the degree of mineralization and biogas production. The experiments were carried out on sludge samples taken from three Polish WWTP Two series are reported for each sludge: one phase digestion with 21 days retention time and two phase digestion with 48 hours of hydrolysis and 21 days of methanogenesis. Two-phase digestion of a mixture of primary and excess sludge resulted in volatile solid (VS) reduction from 56.2 to 65.2%, compared to 43.5-47.5% during one phase digestion. The one phase digester generated 0.28-0.40m(3) of biogas per kg of VS, whereas, in the two phase digestion, the total biogas production was 0.46 to 0.63 m(3)/kg VS.