Long-term effects of sulfite pretreatment on the continuous anaerobic sludge digester for improving methane production and volatile solid reduction: Towards sustainable sludge treatment

Abstract

Using sulfite pretreatment to improve anaerobic sludge digestion has been proved to be effective. However, the effect of sulfite pretreatment on sludge digestion was verified by the batch tests in previous work, and its effects on continuous operation remain unclear, which is crucial to determine the long-term viability of using sulfite pretreatment in the real application. In this study, the impacts of sulfite pretreatment on the continuously operated anaerobic sludge digester were experimentally investigated to reveal its long-term role. The methane production and volatile solid reduction of sulfite-pretreated sludge were significantly improved by 25 % with pretreatment at sulfite of 100 mg S/L, pH of 6 for 24 h, while more ammonium and phosphorus were released during the anaerobic digestion. Moreover, sulfite pretreatment stimulated more organics extracted from sludge for methane conversion. The methanogens and syntrophic bacteria in the bioreactor were spurred by sulfite pretreatment to uptake diverse substrates for methanogenesis. Adopting sulfite pretreatment for sludge management could overall enhance energy recovery by 37.40 %, save operational cost by 31.43 %, and reduce carbon emission by 37.80 %, implying the potential of sulfite-based technology for sludge treatment towards environmental sustainability.