Full scale co-digestion of organic waste.

Operational results of a co-digestion facility were assessed over a period of 18 months. The organic fraction of municipal solid waste (OFMSW) contains a considerable amount of contaminants and grit (up to 6% w/w). A BTA-Pulper efficiently treated the different waste streams and converted a high amount of volatile solids (VS) into the digester feedstock. The seasonal fluctuations of the waste composition significantly influenced the biogas production. The impact of this seasonally variant degradability of VS had to be considered by evaluating the operation results. The waste streams investigated did not show any negative impact on digester performance. The hydraulic retention time (HRT) in the digester considerably affected the VS-reduction. Despite a considerable decrease of VS-degradation a reduction of HRT from 14 to 8 days slightly improves the gas production rate (GPR). An activated sludge system efficiently reduced the pollution of the effluent. The nutrient content of the anaerobic compost was favourable and the content of pollutants was low. The facility produced surplus electrical power up to 290 MJ/t. An overall energy balance shows that the facility substitutes primary energy.