Codigestion of olive oil mill wastewaters with manure, household waste or sewage sludge

Combined anaerobic digestion of oil mill effluent (OME) together with manure, household waste (HHW) or sewage sludge was investigated. In batch experiments it was shown that OME could be degraded into biogas when codigested with manure. In codigestion with HHW or sewage sludge, OME dilution with water (1:5) was required in order to degrade it. Using continuously stirred lab-scale reactors it was shown that codigestion of OME with manure (50:50 and 75:25 OME to manure ratios) was successful with a theoretical OME utilization of 75% and with approx. 87% reduction of the lipids content in OME. An OME utilization of approx. 55%, and lipid reduction of 73% was reached in codigestion with HHW (50:50 and 75:25 OME to HHW ratios). The results showed that the high buffering capacity contained in manure, together with the content of several essential nutrients, make it possible to degrade OME without previous dilution, without addition of external alkalinity and without addition of external nitrogen source.