Mitigation of the Toxicity of Capsaicin on Anaerobic Codigestion of Food Waste and Waste Activated Sludge Using Calcium Peroxide: A Comprehensive Analysis Using Computational and Biological Approaches

Increasing amounts of food waste with high concentrations of capsaicin are generated globally. Capsaicin concentration has been proven to inhibit methane production in the anaerobic codigestion process; thus, strategies to alleviate this toxicity are urgently needed. This study focuses on the use of calcium peroxide for alleviating the inhibitory effect of capsaicin and methane production promotion in anaerobic codigestion for the first time. Results show that calcium peroxide increases the rate of capsaicin degradation significantly. Based on active site prediction, degradation product identification, and density functional theory calculations, the main pathways of capsaicin degradation are verified to be O-demethylation and hydrogen abstraction. According to the quantitative structure–activity relationship, the main degradation products are less toxic than capsaicin. With an increase of calcium peroxide addition from 0 to 0.10 g/g VS (volatile solid), the methane yield and production rate are promoted from 174.92 ± 7.12 mg/g VS and 10.54 ± 0.32 mL/(g VS·d) to 307.56 ± 10.43 mg/g VS and 23.15 ± 0.72 mL/(g VS·d), respectively. This study provides insights into calcium peroxide-enhanced capsaicin degradation and demonstrates an effective niche to mitigate the capsaicin toxicity toward anaerobic codigestion.