Methane Production from Anaerobic Digestion of Sludge Enhanced by Calcium Hypochlorite Treatment with Zero-Valent Iron Regulation
Abstract
Calcium hypochlorite (CH) is a strong oxidant that can be utilized to enhance sludge hydrolysis and anaerobic digestion (AD) performance; however, its suppressive effect on methanogens restricts the development of CH treatment technologies. This laboratory-scale study introduced zero-valent iron (ZVI) into a CH-treated sludge AD system to alleviate the adverse effect, thereby synergistically enhancing biomethane production, and the correlation between methane yield and the two key treatment parameters (ZVI and CH dosages) was explored. The experimental results revealed that the best conditions for the ZVI + CH method were 5 g/L of ZVI plus 0.12 g/g of volatile suspended solids (VSSs) of CH, under which the maximum biomethane yield of 275.8 mL/g VSS was achieved, representing increases of 81.5%, 43.2%, and 28.2% over the control, solo ZVI, and solo CH conditions, respectively. More organic matter in the sludge was found to be degraded during AD by the ZVI + CH treatment compared with the control, solo ZVI, or solo CH conditions. An enzyme activity analysis illustrated that the ZVI + CH treatment not only enhanced the bioactivity of anaerobes but also eliminated the suppression of methanogens by CH. A microbial analysis demonstrated that all functional microbes responsible for sludge AD were enriched by the ZVI + CH treatment, with total abundances of 8.41% and 20.58% in the control and ZVI + CH-treated reactors, respectively.