Successive choline addition enhancing the methanogenesis of waste activated sludge anaerobic digestion: Insight from hydrophilicity, electrochemical performance and microbial community

Abstract

Anaerobic digestion (AD) is a promising technology to treat waste-activated sludge, previous study proved that methane production could be enhanced with the addition of choline, this work aimed to solve the problem of rapid biodegradability of choline in the AD process by changing its dosing method. With 0.75 g/L as the optimal choline dosing concentration, experimental results showed that successive choline dosing during the first 3–6 days of AD (experimental groups, EGs) performed better than the single dosing. The accumulative biogas production in EGs was increased by 35.55–36.73%, which could be caused by the simultaneous promotion of hydrolysis-acidification and methanogenesis processes. Especially, the electron exchange capacity of digested sludge in EGs was increased by 16.71–34.58%. In addition, the surface Gibbs free energy (△GSL) of sludge in EGs was 105.51–172.21% higher (corresponding to stronger hydrophilicity and repulsion), which might help disperse sludge flocs and improve mass transfer efficiency, and the △GSL values were positively correlated with the accumulative methane production (R2 = 0.7029). Microbiological analysis showed that microbial communities in EGs were richer and Methanosaeta was regarded as the dominant species with 15.93–30.08% higher relative abundance with choline addition. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, EGs were found to be more active in metabolism clusters. Collectively, these findings demonstrated that successive choline dosing during the first 3–6 days is an effective and novel method to enhance methane production in AD process.