Abstract
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•Straw-based black liquor was employed to generate H2 via biological dark-fermentation.•Anaerobes immobilised on magnetite nanoparticles improved HY by 2.3-folds.•Digestate-derived biochar enjoyed carbonization properties for using as soil amendment.•Study outcomes are linked to paper industry; crops cultivation; bio-energy production.•H2/biochar promotes sustainable development goals: environmental; economic; social.
Black liquor (BL) rich phenolic and complex compounds is generated from pulp and paper mill manufacturing processes which should be treated before reaching the environment. The potential of achieving several sustainable development goals (SDGs) by recovering energy and valuable by-products from BL was extensively investigated. Results revealed that under a dark-fermentation process, the organic content in BL was effectively bio-degraded by anaerobes to achieve a hydrogen yield (HY) of 0.62 ± 0.04 mol/molglucose. Fortunately, the HY was significantly increased up to 1.41 ± 0.13 mol/molglucose by immobilizing the anaerobes onto magnetite nanoparticles (MN). α-amylase, xylanase, CM-cellulase, polygalacturinase, and protease enzymes activities were increased by 2.3, 23.7, 2.7, 26.8, and 31.1 folds with supplementation of MN. Moreover, the conversion efficiencies of protein and carbohydrate were improved by values of 36 and 113.3% and total phenolic compounds (TPC) were enhanced by 23.5% compared with the control test. Electron-equivalent and COD mass balances were estimated to comprehensively describe the effect of Mn supplementation on the HY performance and fermentation pathways. Digestate generated from the fermentation process was utilized to produce biochar, having C (58.2%), O (32.4%), Na (4.7%), and P (1.1%). The study outputs were interlinked to bio-energy generation, pollution minimization, biochar as a soil amendment, nanoparticles and paper manufacturing industrialization, meeting environmental, economic, and social related SDGs.