Bacteria and Virus Inactivation: Relative Efficacy and Mechanisms of Peroxyacids and Chlor(am)ine

Abstract

Peroxyacids (POAs) are a promising alternative to chlorine for reducing the formation of disinfection byproducts. However, their capacity for microbial inactivation and mechanisms of action require further investigation. We evaluated the efficacy of three POAs (performic acid (PFA), peracetic acid (PAA), and perpropionic acid (PPA)) and chlor(am)ine for inactivation of four representative microorganisms (Escherichia coli (Gramnegative bacteria), Staphylococcus epidermidis (Gram-positive bacteria), MS2 bacteriophage (nonenveloped virus), and Φ6 (enveloped virus)) and for reaction rates with biomolecules (amino acids and nucleotides). Bacterial inactivation efficacy (in anaerobic membrane bioreactor (AnMBR) effluent) followed the order of PFA > chlorine > PAA ≈ PPA. Fluorescence microscopic analysis indicated that free chlorine induced surface damage and cell lysis rapidly, whereas POAs led to intracellular oxidative stress through penetrating the intact cell membrane. However, POAs (50 μM) were less effective than chlorine at inactivating viruses, achieving only ∼1-log PFU removal for MS2 and Φ6 after 30 min of reaction in phosphate buffer without genome damage. Results suggest that POAs' unique interaction with bacteria and ineffective viral inactivation could be attributed to their selectivity toward cysteine and methionine through oxygen-transfer reactions and limited reactivity for other biomolecules. These mechanistic insights could inform the application of POAs in water and wastewater treatment.

Reactivity of Performic Acid with Organic and Inorganic Compounds: From Oxidation Kinetics to Reaction Pathways

“…The reactivity of tryptophan with PFA is also in agreement with the reactivity of protein-like compounds (such as tryptophan and tyrosine) measured by fluorescence spectroscopy during the disinfection of WW . In addition, the lack of PFA consumption by tyrosine, glutamine, histidine, and glycine, indicating their lower reactivity, is consistent with the results of Wang et al, who reported rate constants lower than 0.1 M –1 s –1 for these amino acids at neutral pH (7.1).…”

“…Among the 9 amino acids, cysteine, methionine, and, to a lesser extent, tryptophan were the most reactive with PFA (Figure A). PFA was completely consumed by cysteine (RCR = 0), which is consistent with the high reactivity of cysteine with PAA and the recent findings by Wang et al, showing the higher reactivity of cysteine and methionine with PFA. The reactivity of tryptophan with PFA is also in agreement with the reactivity of protein-like compounds (such as tryptophan and tyrosine) measured by fluorescence spectroscopy during the disinfection of WW .…”

“…However, it is crucial to evaluate the stability, persistence, and potential toxicity of S-oxide, sulfonyl, or N-oxide compounds in the environment to assess their impact compared to their parent molecules. The high selectivity of PFA toward reduced sulfur is also consistent with recent findings showing its high reactivity with cysteine and methionine, responsible for its specific disinfection properties (i.e., bacterial inactivation through accumulation in cells and intracellular oxidation) …”

“…The kinetic rate constants of cysteine and methionine have recently been evaluated for both PFA and PAA, with values reaching >1 × 10 5 M –1 s –1 . This was attributed to the strong susceptibility of the reduced sulfur atom to electrophilic attack, corresponding to an electron transfer mechanism. , The k PFA values of CBZ, SMX, DCF, ACT, FUR, and LID were in the same range as the k PAA values reported for similar nitrogen-containing compounds (from 2.5 × 10 –3 to 1.6 × 10 1 M –1 s –1 ) . The k PFA of some investigated pharmaceutical compounds (SMX and DCF) were about 100 times higher than their reported k PAA values (Table ).…”

Mechanistic Insight for Disinfection Byproduct Formation Potential of Peracetic Acid and Performic Acid in Halide-Containing Water

“…20 mL of regular or saline wastewater (Table S1, Text S1) was buffered with phosphate to the desired pH and spiked with 100 μM of PAA, PFA, or NaOCl in amber glass vials. It is worth noting that these three disinfectants provide comparable bacterial inactivation at the same dosage as demonstrated by our recent study . The reactors were protected from ambient light, stirred vigorously, and sealed with caps with a headspace less than 5 mL.…”