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

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.