Abstract
Coffee grounds are produced about 500,000 tons/year in Japan, and methane fermentation can be an effective treatment method for the waste because energy recovery can be expected. Although there is an actual WWTP producing methane gas by co-digestion with coffee grounds and sewage sludge successfully, unstable condition of coffee grounds fermentation under long time operation is reported and fermentation inhibition can be suspected.
In this study, a series of batch and continuous experiments for thermophilic methane fermentation of coffee grounds were conducted in order to clarify the inhibition property and find its mitigation methods. Batch experiments examined effects of inhibition in residue of thermophilic methane fermentation of coffee grounds on methane production. The result indicated that inhibition in residue affected methane production due to the accumulation of inhibitor, and that it was possible to reduce the inhibition by treatment with activated carbon. Continuous experiments examined effect of co-digestion of coffee grounds with kitchen garbage. The operation was unstable because of accumulating large amounts of VFA when treating only coffee grounds, but after adding more than 8% of kitchen garbage stable operation was achieved with stable pH and methane production.
