Composting of dairy cattle manure using a thermophilic–mesophilic sequence

A thermophilic–mesophilic sequence of composting was compared with continuous thermophilic composting in a small-scale laboratory reactor. Dairy cattle manure was allowed to self-heat adiabatically for one week prior to individual temperature treatments at 20, 37, and 55 °C. Preliminary self-heating was carried out to naturally activated indigenous compost microorganisms to attain thermophilic condition. Microbial activity during composting was monitored by measuring oxygen uptake rate (OUR). Total active microbial biomass was measured using the adenosine triphosphate (ATP) bioluminescence technique. Organic matter degradation was determined by measuring the volatile solids content of compost samples. Results showed that composting at 55 °C promotes the rapid degradation of organic matter as shown by high cumulative oxygen uptake. Composting at 37 °C also exhibited high microbial activity probably due to degradation of complex organic compounds. Microbial biomass was found to be high at 20 and 37 °C, indicating larger microbial communities at lower compost temperatures. Organic matter degradation analysis revealed no large differences in the final solid degradation rate at 55 and 37 °C. The study suggests the importance of a thermophilic–mesophilic sequence in composting to maximise the extent of organic matter degradation.