Batch digestion tests were performe

Batch digestion tests were performed on the unscreened manure, the screened manure fractions (i.e. fine and coarse fractions), the food waste, and two mixtures of manure and food waste. The first mixture contained 32% food waste and 68% unscreened dairy manure, based on volatile solids (VS) and the second contained 48% food waste and 52% unscreened dairy manure. These mixture ratios were specified according to the amount of food waste that could be delivered to an existing dairy farm in Sacramento, CA where the co-digestion practice is intended. This farm raises 1800 cows that produce 83.1 ton of wet manure daily. It was intended to co-digest this amount of manure with either 19.1 and 38.2 ton/day of food waste. These quantities of food waste can be delivered by one or two trucks per day, respectively. The initial volatile solids loadings for the batch digestion of manure (unscreened and screened), food waste, and the mixtures were 5, 2, and 3 gVS/L, respectively. These loading were determined from preliminary experimental results, and were considered appropriate levels for giving relatively a short lag phase of less than 5 days, at the beginning of the digestion tests and also limiting inhibition of the methanogenic bacteria. All the tests were carried out in duplicate using 1-L anaerobic reactors at mesophilic temperature (35 ± 1 °C) for 30 days.