Improved production of medium-chain fatty acids by biochar: Effect of biochar dosage and mechanism

Chain elongation (CE) is a promising technology that can produce medium-chain fatty acids (MCFAs) from sewage sludge, reaching the dual benefits of waste management and clean energy production. The feasibility of using biochar to enhance CE efficiency was examined in this study, where the underlying promoting mechanisms and optimal biochar dosage were also simultaneously explored. Biochar improved the carbon conversion and electron transfer efficiency of CE. The highest caproate concentration (3347.95 mg/L) occurred in the group with 10 g/L biochar addition, and caprylate was most accumulated (612.36 mg/L) when biochar dosage was 20 g/L. The electroactive genera positively related to MCFAs (e.g., norank_f__JG3 0-KF -CM45 and Acetobacterium ) were noticeably enriched by low dosage, but the acidification genera proliferated better under excessive dosage. The different MCFAs production induced by varied biochar dosages was closely related to the genera Dysgonomonadaceae . The strengthened dominant CE pathways, FAB, might account for the promoted MCFAs production.