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Electrochemical pre-treatment of oleate on anaerobic digestion was investigated using two anaerobic filters (AF and AFm) working, respectively, with increasing concentrations of electrochemically pre-treated oleate and oleate. Influents containing 25% and 50% of chemical oxygen demand (COD) of these substrates did not cause relevant alterations in either digester's performance. Comparatively, the pre-treated oleate unit (AF) showed a higher gas production but a lower COD removal than AFm (2.0 vs 1.5 m3 CH4 m-3 d-1; 76-85 vs 91-93% COD removal). The raised AFm COD removal together with the larger proportion of VSS in its effluent than in AF (5.69 vs 0.26 kg m-3) indicate that the biomass washout can be a consequence of the encapsulated solids by lipidic compounds that were not fairly degraded. Further increases of oleate in AFm feed (75 and 100% COD) led to decreases of biogas production to half and COD removal from values higher than 90% to 83-75%. The simultaneous increase of effluent VSS concentrations to 10-12 kg m-3 emphasizes the oleate negative effect. The use of pre-treated oleate as the only carbon source did not influence negatively the AF behaviour in terms of methane production. COD removal was maintained at values higher than 80% and the effluent VSS at low concentrations (0.15 kg m-3). The significantly higher methane yield achieved by AF than AFm indicates a higher accumulation of oleate than pre-treated oleate. Therefore, electrochemical process stands for a suitable pre-treatment for lipid rich effluents, allowing the application of higher organic loads keeping a higher methane yield. [ABSTRACT FROM AUTHOR]

Combined anaerobic digestion of olive mill wastewater (OMW) and piggery effluent (PE) was performed to evaluate the operational conditions required to develop a feasible method of OMW treatment. The effect of concentration and composition on the performance of an up-flow anaerobic filter treating a mixture of these wastes was investigated by gradually increasing the proportion of OMW in the feed from 8% to 83%by volume. Organic loads ranged from 3 to 10 kg COD m{sup}-3{end} d{sup}-1{end}, with substrate organic load ratio (OMW COD/PE COD) varying from approximately 6 to around 30. Hydraulic retention times of 6--7 days were employed throughout. Increases in organic load and feed OMW content resulted in reduced biogas methane contents but higher overall methane production rates. Total COD removal efficiencies of 70--77% were achieved consistently, while the methane yield of 0.341--0.349 m{sup}-3{end} kg{sup}-1{end} total COD removed indicated stable operation even at the highest feed OMW content. [ABSTRACT FROM AUTHOR]