Promoting caproate production using anaerobically digested sludge-derived biochar: Performances, mechanisms, and environmental impacts

Carbon chain elongation offers a promising pathway for converting waste resources into caproate. However, challenges in yield and selectivity have limited its broader application. To address these limitations, anaerobically digested sludge-derived biochar (ADS-B) was incorporated into the carbon chain elongation process. The findings reveal that the addition of 20 g/L ADS-B resulted in the highest net caproate yield (6.5 g/L) and selectivity (61.1%). Further analysis highlighted that ADS-B's superior physicochemical properties enhanced the conversion of butyrate to caproate and facilitated the colonization of key microorganisms, such as Terrisporobacter and Clostridium, essential for caproate production. Additionally, a life cycle assessment indicated that ADS-B addition effectively reduced the environmental impact of caprate production, with additional potential for further mitigation through feedstock substitution. This study provides critical insights into the application of anaerobically digested sludge-derived biochar for enhancing carbon chain elongation, presenting an alternative approach for waste reutilization.