Deciphering the function of coke and C6-homoserine lactone in alleviating capsicum stress during co-anaerobic digestion: Insights into physiological responses and quorum sensing regulation

Anaerobic co-digestion (AcoD) of food waste (FW) and excess sludge (ES) has been widely studied due to its low energy consumption and potential for clean energy production. However, anaerobic inhibitory substances like capsaicin in FW and system instability often limit its performance. This study investigated the effects of coke and C6-homoserine lactone (C6-HSL) as exogenous additives on enhancing AcoD under capsicum stress. The results showed that simultaneous addition of coke and C6-HSL promoted dissolution, hydrolysis, acidogenesis, and methanogenesis, facilitated microbial aggregation, and converted solid and liquid phosphorus into gaseous phosphorus. These additives increased the abundance of key microorganisms such as Euryarchaeota, Thermotogota, Methanosarcina, and Syntrophomonadaceae, enhanced phosphate and succinate production, and upregulated genes related to ATP and NADH synthesis (e.g., atpA, atpB, nuoF). The expression levels of atpA, atpB, and nuoF increased from 0.1202%, 0.0463%, and 0.1120% to 0.1914%, 0.0919%, and 0.3834%, respectively. This study provides operational strategies to mitigate capsaicin inhibition and offers theoretical guidance in biomass energy conversion for practical applications.