Electrically conductive materials enhance the dark fermentation of cheese whey

Background and Aims Cheese manufacturing relies on high energy consumption, thus the development of novel strategies for in-situ energy production using alternative fuels would be beneficial for a more sustainable production. Cheese whey (CW) is a residue that remains after the recovery of the curd from the clotting of milk. CW can be treated by dark fermentation which converts sugars and other substances into fatty acids with simultaneous H2 production. H2 can then be used for in-situ electrical energy generation using conventional fuel cells; similarly, the produced fatty acids can be valorised by chemicals production. The aim of this study was to evaluate the efficacy of different electrically conductive materials (ECMs) on the rate and yield of H2 and fatty acids production during CW dark fermentation. Methods CW was fermented in the presence of different ECMs (i.e., biochar, magnetite and graphite). The concentration of volatile fatty acids (VFAs), lactic acids, and H2 was monitored over time. The bacterial communities were characterized by high-throughput sequencing of 16S rRNA gene amplicons. Results Fermentation tests evidenced that the production of H2 and VFAs was enhanced (up to ten-fold) in the presence of ECMs, with biochar displaying the most promising results. Conclusions The stimulatory effect likely resulted from the conductive particles facilitating the establishment of direct interspecies electron transfer processes among syntrophic partners. This work was co-financed by the Italian Ministry of University and Research during the research program PRIN 2022 PNRR “Valorization of cheese whey by hydrogen production in bio-electrochemical systems catalyzed with purple bacteria (WHISPER)”.