Co-digestion of press water and food waste in a biowaste digester for improvement of biogas production

Co-digestion of press water from organic municipal wastes and of homogenized food residues with defibered kitchen wastes (food waste) as the main substrate was examined to improve biogas production. Although the biowaste digester was operated already at high organic loading (OLR) of 12.3 kg COD m−3 d−1 during the week, addition of co-substrates not only increased biogas production rates but also improved total biogas production. By feeding the two co-substrates up to 20 kg COD m−3 d−1 gas production followed the increasing OLR linearly. When the OLR was further increased with food waste, not more gas than for 20 kg COD m−3 d−1 OLR was obtained, indicating the maximum metabolic capabilities of the microbes. During weekends (no biowaste available) food waste could substitute for biowaste to maintain biogas production. Addition of press water or food waste to biowaste co-digestion resulted in more buffer capacity, allowing very high loadings without pH control.