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

This study deals with the treatment of a potent two-phase olive mill waste (TPOMW) through the degradation of its phenolic content, with simultaneous bio-electrochemical reduction of CO2 to CH4, using a dual-chamber Microbial Electrolysis Cell (MEC). The MEC operated for 120 days and the effects of different dilutions (1:10, 1:5 and no dilution) and applied potentials (0.5 V and 1 V) on its performance were studied. The results showed that decreasing the dilution (from 1:10 to 1:5 and to no dilution) 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 0.08, to 0.48 and to 2.33 mmols, 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 to 91%, while the produced CH4 further increased to 2.88 mmols. The results indicate that the MEC technology can be potentially exploited for the treatment of the potent TPOMW and produce CH4 as a waste-to-energy source.