Long-term effects of nickel oxide nanoparticles on the physicochemical properties and microbial metabolism of activated sludge
In order to reveal the biotoxicity of nickel oxide nanoparticles(NiO NPs)in complex environmental systems,this study used activated sludge as the research target and investigated the long-term effects of NiO NPs(0～200mg/L)on the operational efficacy,sludge performance,and microbial metabolism of sequencing batch reactors.Results indicated that low concentrations(0～50mg/L)of NiO NPs did not have significant effects on activated sludge operational efficacy,and high concentrations(100～200mg/L)of NiO NPs significantly inhibited the removal of ammonia nitrogen and COD by 8％and 20％,respectively.With the increase of the concentration of NiO NPs,the activities of key functional enzymes ammonia monooxygenase(AMO)and hydroxylamine oxidase(HAO)in the nitrification process decreased by 55.71％and 62.09％,respectively,and the release amounts of lactate dehydrogenase(LDH)increased by 113.06％.Meanwhile,NiO NPs negatively affected activated sludge flocculation,with an increase in average sludge particle size,loose floc shape,and a slight decrease in flocculation.Extracellular polymeric substances(EPS)showed an overall decreasing trend,the intensities of protein-related(N-H,C=O)and polysaccharide-related(C—O,C—C,C—O—C,C-O-H)functional groups weakened at high concentrations,and the intensities of the proteins characteristic peak of three-dimensional fluorescent decreased substantially.However,biodegradation of dead microorganisms and stress response promoted microbial metabolism and tyrosine protein-like substance production in EPS.In addition,the diversity and stability of microbial communities in activated sludge were both affected by NiO NPs.PICRUSt2prediction showed that metabolic pathways related to metabolisms and genetic information processing were both significantly inhibited by NiO NPs.Therefore,NiO NPsaffected nitrification and organic matter removal of activated sludge by altering microbial community structure and metabolic pathways.
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