New insights into different surfactants’impacts on sludge fermentation:Focusing on the particular metabolic processes and microbial genetic traits

Surfactants were expected to exhibit positive effects on the waste activated sludge(WAS)disposal.However,the systematic comparison of different categories of surfactants on the WAS fermentation and the functional mechanisms,especially microbial metabolic traits,have not yet been precisely explored.This study revealed the positive effects of different surfactants on the volatile fatty acid(VFA)production,which followed the order of alkyl polysaccharides(APG)>sodium dodecylbenzene sulfonate(SDBS)>hexadecyl trimethyl ammonium bromide(HTAB).Mechanistic exploration found that the presence of different surfactants improved solubilization and hydrolysis steps,and then contributed to the subsequent acidification with different efficiencies.The functional microorganisms associated with VFA generation were enriched in surfactant-conditioned reactors.Metagenomic analysis further indicated that the key genes involved in the particular process of VFA generation were over-expressed.The simultaneous bioavailable substrate improvement,functional bacterial enrichment,and metabolic activity upregulation induced by different surfactants jointly contributed to VFA promotion during WAS fermentation.This study could provide a comprehensive realization of surfactants’impacts on theWAS fermentation process,and more importantly,it reminded the public to discern the distinct interplaying effects induced by different chemicals in regulating the WAS disposal and resource recovery.