Anaerobic co-treatment of olive mill and piggery effluents

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 influent concentration and composition on the performance of an upflow 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(-3) d(-1), 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(-3) kg(-1) total COD removed indicated stable operation even at the highest feed OMW content.