Two-Stage Anaerobic Digestion Process Combining Pre-digestion with Methanization

Abstract

Anaerobic digestion of a mixture of manure and sewage sludge by combination of the biological predigestion at 73°C with methanization at 55°C was studied with regard to the biogas process efficiency,
energy balance and sanitation effect. Performance of the two-stage digestion was compared with the
conventional, one-stage moderate thermophilic digestion at 55°C and mesophilic digestion at 37°C,
respectively. The best performance was achieved by the two-stage treatment both in terms of Volatile
Solids (VS) removal and biogas yield. Up to 60% of VS was removed and a specific methane yield of 300
ml CH4 gVS-1 was achieved. Sanitation effect was measured as inactivation of the indicators of bacterial
pathogens - the faecal enterococci and spores of Clostridium perfringens. Elimination of faecal enterococci
to non-detectable level occurred only during treatments at 73°C and 55°C. Numbers of Clostridium
perfringens spores were reduced solely by the combined 73°C/55°C treatment.