Fermentation-based nanoparticle systems for sustainable conversion of black-liquor into biohydrogen

Paper-manufacturing industries utilize rice straw (RS) as raw material, generating huge quantity of black liquor (BL), which should be treated before reaching the environment. BL is mainly rich in organic pollutants that can be utilized to obtain valuable by-products and meet sustainable development goals (SDGs). In this investigation, BL from a paper-making industry was efficiently employed as a substrate for bio-H2 generation via dark fermentation at pH value of 7.5 and temperature of 35 °C for 14 days, resulting in a hydrogen yield (HY) of 0.579 mol/molglucose. The HY was substantially increased up to 1.654, 1.908, and 2.187 mol/molglucose with immobilization of anaerobes on Graphene (GN), hydroxyapatite (HN), and Graphene/hydroxyapatite nanoparticles (GHN). Further, the activities of protein- and carbohydrate-degrading enzymes i.e. protease, α-amylase, xylanase, and CM-cellulase was highly improved. Results were validated with respect to the operational taxonomical unit (OUT) richness estimators (ACE and Chao), diversity indices (Shannon and Simpson), and electron-equivalent and mass balances. The H2 productivity data were techno-economically assessed for proposing a bioenergy-based project, revealing a payback period of 5.92 y to recoup the initial investment. The findings of this study would promote interaction in the areas of industrialization, pollution prevention, and clean energy production to attain SDGs keys.