Effect of peracetic acid solution on a nitrifying culture: Kinetics, inhibition, cellular and transcriptional...

Peracetic acid (PAA) has been widely used as a disinfectant in many industries. However, information related to the potential inhibitory effect of PAA solutions (PAA and H₂O₂) on biological wastewater treatment processes is very limited. The work reported here assessed the effect of PAA and H₂O₂ solutions on nitrification kinetics and inhibition, cellular level responses and gene expression of a suspended-growth nitrifying culture. The initial ammonia removal and nitrate production rates significantly decreased at 1/0.14 to 3/0.42 mg/L PAA/H₂O₂. H₂O₂ up to 3 mg/L did not impact nitrification, cell viability or related respiratory activities; thus, the impact of the PAA solution is attributed to PAA alone or in some combination with H₂O₂. Nitrification inhibition by PAA was predominantly related to enzyme inhibition, rather than to loss of cell viability and/or cell lysis. PAA and H₂O₂ negatively affected Nitrosomonas but resulted in Nitrosospira enrichment. Most nitrogen metabolism-related genes (e.g., hydroxylamine oxidoreductase and nitrite oxidoreductase genes) as well as oxidase genes (e.g., cytochrome c oxidase, catalase-peroxidase, and peroxidase genes) were upregulated in PAA- and H₂O₂-amended cultures. Major ATPase genes were downregulated while ATP synthase genes upregulated under the effect of PAA and/or H₂O₂. Upregulation of ATP-dependent protease genes indicates protein damage predominantly caused by PAA rather than H₂O₂. The transcriptional level of genes related to cell division and DNA repair did not show a particular pattern; thus, cell division functionality and DNA integrity were not significantly affected by PAA or H₂O₂. The results of this study have significant implications in the design and operation of effective biological nitrogen removal systems for the treatment of PAA-bearing wastewater.