Peroxyacids (POAs, e.g., performic acid (PFA), peracetic acid (PAA), and perpropionic acid (PPA)) are proposed as alternatives to chlorine-based disinfectants to reduce the formation of halogenated disinfection byproducts. However, the three POAs have never been systematically compared with free chlorine/chloramine for bacterial and viral inactivation performance in the same water matrix. In the present study, we compared the bacterial inactivation efficiency of PFA, PAA, PPA and free chlorine/chloramine in an anaerobic wastewater effluent, using Escherichia coli and Staphylococcus epidermidis as representatives for Gram-negative and Gram-positive bacteria. We also investigated the three POAs and free chlorine for viral inactivation in phosphate-buffered solutions, using MS2 and Phi6 as representatives for nonenveloped and enveloped viruses. Experimental results showed that the bacteria inactivation efficacy followed the order of PFA &gt; chloramine &gt; PAA ≈ PPA. Investigation by fluorescence microscopy indicated that chlorine and POAs interact with E. coli via different mechanisms. Briefly, free chlorine induces surface damages and cell lysis rapidly, whereas POAs mainly lead to intracellular oxidative stress through penetrating the intact cell membranes. In contrast to free chlorine, POAs, being more selective oxidants, are less consumed by extracellular/surface components and can accumulate inside the cells. For viral inactivation, PFA and PAA achieved only ~1-log PFU removal for both viruses after 30-min reaction. These results were surprising considering that: (1) PFA has been suggested in limited studies to inactivate various pathogens more efficiently than PAA; and (2) the enveloped Phi6 appeared to be even more resistant to POAs than the nonenveloped MS2. Subsequent genome measurements (RT-qPCR) and abiotic reactivity tests revealed that PFA and PAA were both highly selective oxidants toward cysteine and methionine through oxygen-transfer reactions, while exhibited sluggish reactivity for other amino acids and ribonucleotides. Thus, viruses that lack cysteine and methionine on the surfaces (such as MS2 and Phi6) could exhibit strong resistance to POAs, regardless of the viral structures and POA types.

Understanding pathogen inactivation by peroxyacids

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