Thermophilic anaerobic digestion of alcohol distillery wastewaters

Results are presented from a full-scale plant using thermophilic (50–55°C) anaerobic digestion of waste-waters from an alcohol distillery. The distillery processes mainly beet molasses, but also molasses from figs, raisins and wines. A new version of the process is described, where the digester has a feedback of bacteria and undigested solids, in order to overcome high sulfate and nitrogen concentrations and the high organic load of the effluent. The best results for a waste feed with 60 g/liter COD were found to be the following: volumetric load up to 6 kg/m 3 day, biogas production about 2·5 m 3/m reactor 3 day (76% CH 4 content), methane production 0·4 m 3/kg COD removed, efficiency in converting organic solids to CH 4 70%, and mean CO 2 content of biogas 18%.