The prospective of table olive debittering & washing Effluent (DWE) as feed stock wastewater for anaerobic digestion (AD) systems was investigated in batch and continuous systems together with cattle and pig manures. While OWE considered unsuitable for biological treatment methods due to its unbalanced nature, she co-digestion of the wastewaters resulted in a 50% increase in the methane production/gram volatile solids(added) (CH(4)/gVS(added)), accompanied by 30% phenol reduction and 80% total organic carbon removal (TOC). pH increase during the co-digestion period was not identified as an inhibitory factor and all reactors were able to withstand this operational condition change. Moreover, no volatile fatty acid (VFA) accumulation was observed, indicating that the reactors were not operating under stress-overloading state. Under thermophilic conditions a 7% in :tease on the TOC removal efficiency was achieved when compared to the mesophilic systems while, under mesophilic conditions phenolic compounds reduction was 10% higher compared to the thermophilic systems. (C) 2011 Elsevier Ltd. All rights reserved.