Characterizing Food Waste Substrates for Co-Digestion through Anaerobic Toxicity Assays (ATA) and Biochemical Methane Potential (BMP)

Co-digestion of food waste with dairy manure is increasingly utilized; however, there is a lack of information on appropriate substrates. In this study, anaerobic toxicity assays (ATA) and biochemical methane potential (BMP) tests were conducted to determine the suitability of four food waste substrates (meatball, chicken, cranberry and ice cream processing wastes) for co-digestion with dairy manure. In the ATA, inhibition was observed at concentrations above 5% for all four food waste substrates, with up to 99% decrease in biogas production at the 30% inclusion rate. While an excess of sodium bicarbonate was added through media addition, there were significant decreases in pH for almost every treatment, illustrating the importance of co-digesting with a high alkalinity substrate when food processing wastes are added. The BMP experiments co-digested the four food waste substrates with flushed dairy manure at a substrate ratio of 3.2% food waste and 96.8% manure (by volume), which equated to 14.7% (ice-cream) to 80.7% (chicken) of the VS being attributed to the food waste. Increases in methane production from 67.0% (ice cream waste) to 2940% (chicken processing waste) were observed in the food waste treatments compared to digesting manure alone, demonstrating the large potential increases in methane production with food waste addition. Due to manure co-digestion, there were no decreases in pH and no media was added. These studies illustrate that large potential of food waste addition for increased methane production, but also convey the caution that must be taken when adding food waste to anaerobic digestion systems.