Effect of trace element supplementation on the mesophilic anaerobic digestion of foodwaste in batch trials: the influence of inoculum origin

Batch anaerobic trials using a source-separated food waste as a substrate with inoculums of different origins were carried out under mesophilic conditions. Reactions were operated both with and without trace element (Co, Mo, Ni, Se, W) supplementation. Supplementation with trace metals had either neutral or slightly negative effects with inoculums originating from reactors with a high background level of metals, such as those for the co-digestion of biowaste and waste activated sludge. For inoculums from reactors treating food waste only, which inherently contain low levels of trace metals, supplementation with these metals increased methane production. In particular, Mo concentrations in the range of 3-12 mg per kg dry matter and Se concentrations of 10 mg per kg dry matter increased methane production to as high as 30-40%. Supplementation with a metal mixture (Co, Mo, Ni, Se and W) increased the methane production to the range 45-65% for inoculums with low background concentrations of trace metals. These findings may have an important impact in the commercial production of methane from food waste.