Anearobic digestion of piggery waste. 3. Influence of temperature

Abstract

The effects of temperature in the range of 13 to 55 C on the digestion of wet piggery manure were investigated in laboratory-scale digesters fed daily at a load of approx. 4 kg TS (total solids) m-3 day-1 . At a digestion temperature of 13 C no methane was produced. In the mesophilic temperature range (20 -40 C) the methane production increased with temperature particularly in the range of 20 to 25 C. In the range of 25 to 40 C the increase of the methane production was much less pronounced and hydrolysis of undissolved manure components turned out to be the rate limiting step of the digestion process. Under thermophilic con ditions (55 C) the methane production decreased with approx. 25 % as compared to mesophilic digestion in spite of a somewhat higher degree of hydrolysis. Thermo philic digestion appeared to be more sensitive for high ammonia-nitrogen concen trations than mesophilic digestion which presumably is caused by an increase in the fraction of free ammonia with temperature (at constant pH and total ammonia cal nitrogen concentration).