Codisposal of municipal refuse, sewage sludge and marine dredgings for methane production

As marine disposal of sewage sludge and dredged sediments may impose serious adverse effects to marine ecosystems, landfilling seems to be the most feasible method for the final disposal of these wastes. A batch experiment was conducted to study waste degradation and gas production after sewage sludge and marine dredgings were mixed with municipal refuse at 13 different ratios for 36 days. The addition of sludge and dredgings to municipal refuse enhanced gas production, compared with the degradation of refuse or sludge alone. A proper mixing ratio of wastes can also shorten the time to reach the final phase of anaerobiosis. The highest gas production was obtained from the ratio of 75–20–5 (refuse–sludge–dredgings) (wet weight basis). Its average daily gas production rate was 1.42 l kg−1 waste mixture; methane content was 68.3%. The results indicated that codisposal of the three wastes would be beneficial for energy recovery from landfill gas.