Co-digestion of food waste in a municipal wastewater treatment plant: Comparison of batch tests and full-scale experiences

•Co-digestion of raw sludge and food waste was studied.•Results from batch trials were compared with full-scale experiences.•Mass balance of WWTP revealed a rise of 18% compared to batch tests.•Share of self-generated energy has more than doubled with 10% food waste. The effects of co-digestion of food waste in a municipal wastewater treatment plant (WWTP) were studied in batch tests. The results obtained were compared with the mass balance of a digester at a full-scale WWTP for a one-year period without and with the addition of co-substrate. The specific methane yield calculated from the balance was 18% higher than the one in the batch tests, suggesting a stimulation of methane generation by co-digestion. It was hypothesized that this increase was caused by shifting the C/N ratio of raw sludge (8.8) to a more favourable ratio of the added food waste (17.7). In addition, potential benefits by adding food waste for energy autarky was investigated. While just 25% of the total energy demand of the plant could be recovered by biogas generation when no co-substrate was fed, this percentage has more than doubled when food waste was added at a ratio of 10% (w/w).