Efficient anaerobic mono-digestion of N-rich slaughterhouse waste: Influence of ammonia, temperature and trace elements

Three mono-digestion experiments treating slaughterhouse waste with high TKN concentration (∼11 g/kg) were applied in lab-scale at mesophilic and psychrophilic conditions to study the impact of high ammonia concentrations and additives. Precipitation of sulphur by addition of ferrous chloride did not influence process behaviour, whereas supplementation of trace elements significantly improved process stability by reducing volatile fatty acid concentration towards zero. mit of NH4-N concentration causing a rise of VFAs to 19,000 mg/l and reduction of methane by 25% was found between 7.7 and 9.1 g/kg which correspond to NH3 concentrations of 830–1060 mg/l. ophilic operation (25 °C) lowered inhibitory NH3 concentration to 140 mg/l, but process performance was stable only at low OLR of 0.4 kg VS/m3 d. performance at highest possible NH4-N concentration (7.7 g/kg), low VFA accumulation and satisfying methane yield of about 280 Nm3/t COD was observed at OLR of 2.5 kg VS/m3 d at 37 °C.