Treatment of two-phase olive mill waste and degradation of phenolic compounds with simultaneous bio-electrochemical conversion of CO2 to CH4 using a microbial electrolysis cell

Abstract

This study deals with the treatment of a two-phase olive mill waste (TPOMW), with simultaneous bio-electrochemical reduction of CO2 to CH4 using a Microbial Electrolysis Cell (MEC). For this purpose, a dual-chamber MEC was constructed using carbon felt as anodic and cathodic electrodes. The performance was assessed in terms of COD removal, the degradation of the phenolic compounds as well as the electromethanosynthesis potential of the MEC bio-cathode. The MEC operated for 120 days and the results showed that increasing the concentration from 3 to 7 and 38 gCOD/L led to an increase of the COD removal from 74%, to 77% and to 87%, respectively, of the total phenolic content removal from 73%, to 76% and to 79%, respectively, as well as of the produced CH4 from 0.04, to 0.09 and to 0.07 mmols/gCODconsumed, respectively. Increasing the applied potential from 0.5 V to 1 V, while the TPOMW was employed in the anode with no dilution, resulted in further increase of both the COD and the total phenolic content removal from 87% to 79%, respectively, to 91%, while the produced CH4 further increased from 0.07 to 0.08 mmols/gCODconsumed. The results indicate that the MEC technology can be potentially exploited for the treatment of the TPOMW and produce CH4 as a waste-to-energy source.