Optimisation and inhibition of anaerobic digestion of livestock manure

Abstract

The objectives of this study were to:(1) optimise methane production of livestock manure during anaerobic digestion, focusing on the addition of mixed enzymes, thermal pre-treatment and codigestion, and (2) develop a better understanding of ammonia and sulphide inhibition during digestion of animal manure . Enzyme addition increased methane yield of manure following incubation prior to digestion. Thermal pre-treatment increased methane yield but was only energetically favourable when a surplus of thermal energy was available. Digestion of acidified manure showed sulphide inhibition but no inhibition was measured when processing solid fractions of acidified manure. Co-digestion of non-acidified manure with the solid fractions of acidified manure was found to be a promising method of increasing methane yield in terms of digester volume. Total volatile acids, isobutyric and isovaleric acid and total ammonia nitrogen were found to be useful indicators of ammonia inhibition.