Evaluating the toxicity of food processing wastes as co-digestion substrates with dairy manure

•ATAs were conducted on four food processing wastes at 2%, 5%, 15% and 30% (by volume).•There were significant decreases in pH, with media addition, at each inclusion rate.•Above 5% inclusion, all four food processing wastes showed signs of toxicity.•Without co-digestion, CH4 production may be inhibited with food processing wastes.

Studies have shown that including food waste as a co-digestion substrate in the anaerobic digestion of livestock manure can increase energy production. However, the type and inclusion rate of food waste used for co-digestion need to be carefully considered in order to prevent adverse conditions in the digestion environment. This study determined the effect of increasing the concentration (2%, 5%, 15% and 30%, by volume) of four food-processing wastes (meatball, chicken, cranberry and ice cream processing wastes) on methane production. Anaerobic toxicity assay (ATA) and specific methanogenic activity (SMA) tests were conducted to determine the concentration at which each food waste became toxic to the digestion environment. Decreases in methane production were observed at concentrations above 5% for all four food waste substrates, with up to 99% decreases in methane production at 30% food processing wastes (by volume).