Bacterial antioxidant mechanism in calcium peroxide aided sludge anaerobic fermentation

Although calcium peroxide (CaO₂) can enhance the short-chain fatty acids (SCFAs) production in sludge anaerobic fermentation, the microbiological mechanisms underlying this process remain unclear. In this study, it is aimed to elucidate the bacterial protective mechanisms in response to the oxidative stress induced by CaO₂. Results show that extracellular polymeric substance (EPS) and anti-oxidant enzymes play vital roles in protecting bacterial cells from CaO₂. The addition of CaO₂ resulted in increased relative abundances of genes exoP and SRP54, which are associated with EPS secretion and transportation. Superoxide dismutase (SOD) played a crucial in alleviating oxidative stress. The dosage of CaO₂ significantly influences the succession of the bacterial community in the anaerobic fermentation system. With 0.3 g CaO₂/g VSS, the net income was approximately 4 USD/ton of sludge treated. The CaO₂-assisted anaerobic fermentation process has the potential to recover more resources from sludge and thus, benefit the environment.