Antagonistic effects of surfactants and CeO2 nanoparticles co-occurrence on the sludge fermentation process: Novel insights of interaction mechanisms and microbial networks

Various pollutants commonly co-exist in the waste active sludge (WAS), but the interactive effects and mechanisms of co-occurrence pollutants on the WAS treatment remain unclear. This work mainly investigated the impacts of different surfactants ( i.e., HTAB and SDBS) and CeO 2 nanoparticles (NPs) co-occurrence on the WAS fermentation for short-chain fatty acids (SCFAs) production, and found that the CeO 2 NPs coexisting with surfactants caused antagonistic effects on the SCFAs generation (10.7% and 33.9% inhibition by HTAB and SDBS , respectively). The surfactants and CeO 2 NPs co-occurrence restrained the solubilization , hydrolysis , and acidification steps simultaneously. Moreover, the functional hydrolytic-acidogenic bacterial ( e.g., Haliangium and Bacteroidetes sp. ) and the microbial metabolic networks involved in extracellular hydrolysis ( e.g., pepd and NEU1 ), substrate metabolism ( e.g., ALDO and asdA ), and fatty acid biosynthesis ( e.g. , aarC and pct ) were all downregulated by 4.3–53.8% in the reactors with surfactants and CeO 2 NPs co-occurrence. The presence of surfactants enhanced the dispersibility and stability of CeO 2 NPs and the Ce dissolution (1.5–3.0 times higher). Also, surfactants contributed to the WAS disintegration, which could improve the interactive chances of microorganisms entrapped in WAS and CeO 2 NPs by promoting the transportation channels, and therefore aggravated the toxicity towards anaerobic species.