Hydrogen production in microbial electrolysis cell and reactor digestate valorization for biochar – a noble attempt towards circular economy

The relevance of sustainability through circular economy has focused on exploring biomass for biofuels and subsequent reactor digestate waste valorization. This noble study has investigated the bio-hydrogen production from sugarcane bagasse fed membrane-less single-chambered microbial Electrolysis Cell (SC-MEC). Also, the consequent biochar production from the MEC reactor digestate to promote maximum energy extraction from waste was explored. The bagasse in MEC resulted in 0.25 m3 of hydrogen/m3/day at an externally applied voltage supply of 0.8 V, with coulombic efficiency (CE) of 82.87 ± 2% and electrical energy efficiency of 97.47 ± 2%. The cathode and the Shewanella sp. Enriched bioanode were arranged for overpotential reduction, resulting in a high current density of 62 A/m2. The bio-remediation efficiency of SC-MEC was estimated in terms of COD removal reported as 31.16 ± 0.5%, nitrate removal as 28.18 ± 0.2%, and sulphate removal as 41.2 ± 0.2%. The reactor digestate was pyrolyzed, and the biochar yield was calculated as 17.8 ± 0.2%, with BET surface area of 8.903 m2/g. The fixed carbon content of digested bagasse was reported as 22.9 ± 0.2, while the total carbon lost during microbial digestion in SC-MEC was around 32 ± 0.2%. This study paves a route for a circular economy by practicing clean renewable energy and using the reactor waste for subsequent biochar production.