Enhancing energy recovery from cheese whey through dark fermentation combined with different bio-electrochemical processes

In this work, a multi-stage layout for the valorization of cheese whey is proposed, investigating the possibility of recovering energy in various forms through different bio-electrochemical systems. The first stage presents the dark fermentation combined with an electrochemical method for H2 and electricity production. Subsequently, two post-treatment stages are tested for the fermentate utilization, a single-chamber microbial fuel cell, featuring an innovative configuration consisting of four air cathodes with fly ash as the oxygen reduction catalyst, and a dual-chamber MEC, equipped with a bioanode and a biocathode. The latter allows for CO2 conversion to bio-methane in the cathodic chamber, providing a considerable benefit for the conversion of the CO2 produced during the degradation of the substrate. In the first stage, the integrated bio-electrochemical process shows a threefold H2 production yield compared to conventional dark fermentation. Moreover, both microbial cells are proved suitable for the utilization of the organic matter contained in the fermentate, with COD removal yields of over 97%, energy recovery in the MFC at a maximum power density of 1.2 W/m3, and a methane output in the MEC of 0.93 mmol CH4/g COD with 74% of electron recovery.