Enhanced Anaerobic Sludge Digestion by Calcium Peroxide Pretreatment Combined with Manganese Dioxide: Performances and Mechanisms

Anaerobic digestion (AD) of waste-activated sludge for producing methane is a sustainable and efficient sludge treatment technology, yet it faces challenges such as a slow hydrolysis rate and a low methane production rate. This study proposes a novel approach combining calcium peroxide (CaO2) pretreatment and manganese dioxide (MnO2) addition to address these limitations. CaO2 disrupts extracellular polymeric substances and enhances hydrolysis, while MnO2 facilitates direct interspecies electron transfer, boosting the microbial activity and methane production. The results showed that the cumulative methane production increased by 32.22% and 19.91% via the novel combination compared to MnO2 or CaO2 treatment alone. The activity of coenzyme F420 and electron transport system increased to 146.26% and 144.71%, respectively. In addition, microbial community analysis showed that the novel combination enriched hydrogenotrophic methanogens of Methanobacterium and Methanobrevibacte and acetotrophic methanogens of Methanosarcina. The synergistic effect between Geobacter bacteria and Methanosarcina or Methanosaeta increased the methane yield. The emergence of direct electron transfer in microbial communities as an alternative or supplement to indirect electron transfer (via hydrogen or formic acid) significantly improved microbial metabolic activity during AD, which could accelerate organic matters decomposition and methane production. This study provides an efficient sludge treatment way for bioenergy recovery through methane production.