Two-phase anaerobic digestion of solid wastes by a multiple liquefaction reactors process

A new solid-waste treatment process was applied to different vegetable substrates: potato peelings, green salad leaves, green peas mixed with carrots, apple pomace. It involved, at a laboratory scale, several liquefaction digesters, each of them treating one type of waste, coupled to a central methane fixed-film reactor. The influence of pH, load and hydraulic retention time on the process performances was studied at 35°C. On average, except for apple pomace, hydrolysis yields were high (up to 80%) during the liquefaction step. Likewise, the mixture of the acidogenic effluents was degraded in a methanation reactor to an extent of 80%. In a final run with average values near 4 g COD l−1 day−1 for loading rate, and 17 days for hydraulic retention time, overall organic matter removal reached 87%.