Thermodynamic properties of an emerging chemical disinfectant, peracetic acid

Performic Acid Disinfection of Municipal Secondary Effluent Wastewater: Inactivation of Murine Norovirus, Fecal Coliforms, and Enterococci

Performic acid (PFA) is an emerging disinfectant to inactivate bacterial and viral microorganisms in wastewater. In this study, the inactivation kinetics of murine norovirus (MNV) by PFA, in phosphate buffer and municipal secondary effluent wastewater, are reported for the first time. PFA decay followed first-order kinetics and the inactivation of MNV was governed by the exposure of microorganisms to PFA, i.e., the integral of the PFA concentration over time (integral CT or ICT). The extension of the Chick-Watson model, in the ICT domain, described well the reduction of MNV by PFA, with determined ICT-based inactivation rate constants, k_d, of 1.024 ± 0.038 L/(mg·min) and 0.482 ± 0.022 L/(mg·min) in phosphate buffer and wastewater, respectively, at pH 7.2. Furthermore, the simultaneous PFA inactivation of MNV and fecal indicators indigenously present in wastewater such as fecal coliforms and enterococci showed that 1-log reduction could be achieved with ICT of 2, 1.5, and 3.5 mg·min/L, respectively. When compared with the most commonly used peracid disinfectant of municipal wastewater, peracetic acid (PAA), the ICT requirements determined using the fitted ICT-based kinetic models were ∼20 times higher for PAA than PFA, indicating a much stronger inactivation power of the PFA molecule.

Activation of Peracetic Acid with Lanthanum Cobaltite Perovskite for Sulfamethoxazole Degradation under a Neutral pH: The Contribution of Organic Radicals

Advanced oxidation processes (AOPs) are effective ways to degrade refractory organic contaminants, relying on the generation of inorganic radicals (e.g., ^•OH and SO₄^•-). Herein, a novel AOP with organic radicals (R-O^•) was reported to degrade contaminants. Lanthanum cobaltite perovskite (LaCoO₃) was used to activate peracetic acid (PAA) for organic radical generation to degrade sulfamethoxazole (SMX). The results show that LaCoO₃ exhibited an excellent performance on PAA activation and SMX degradation at neutral pH, with low cobalt leaching. Meanwhile, LaCoO₃ also showed an excellent reusability during PAA activation. In-depth investigation confirmed CH₃C(O)O^• and CH₃C(O)OO^• as the key reactive species for SMX degradation in LaCoO₃/PAA system. The presence of Cl^- (1-100 mM) slightly inhibited the degradation of SMX in the LaCoO₃/PAA system, whereas the addition of HCO₃^- (0.1-1 mM) and humic aid (1-10 mg/L) could significantly inhibit SMX degradation. This work highlights the generation of organic radicals via the heterogeneous activation of PAA and thus provides a promising way to destruct contaminants in wastewater treatment.

Application of Cobalt/Peracetic Acid to Degrade Sulfamethoxazole at Neutral Condition: Efficiency and Mechanisms

An advanced oxidation process of combining cobalt and peracetic acid (Co/PAA) was developed to degrade sulfamethoxazole (SMX) in this study. The formed acetylperoxy radical (CH₃CO₃^•) through the activation of PAA by Co (Co²⁺) was the dominant radical responsible for SMX degradation, and acetoxyl radical (CH₃CO₂^•) might also have played a role. The efficient redox cycle of Co³⁺/Co²⁺ allows good removal efficiency of SMX even at quite low dosage of Co (<1 μM). The presence of H₂O₂ in the Co/PAA process has a negative effect on the degradation of SMX due to the competition for reactive radicals. The SMX degradation in the Co/PAA process is pH dependent, and the optimum reaction pH is near-neutral. Humic acid and HCO₃^- can inhibit SMX degradation in the Co/PAA process, while the presence of Cl^- plays a little role in the degradation of SMX in this system. Although transformation products of SMX in the Co/PAA system show higher acute toxicity, the low Co dose and SMX concentration in aquatic solution can efficiently weaken the acute toxicity. After reaction in the Co/PAA process, numerous carbon sources that could be provided for bacteria and algae growth can be produced, suggesting that the proposed Co/PAA process has good potential when combined with the biotreatment processes.

Peracetic acid: Structural elucidation for applications in wastewater treatment

Peracetic acid (PAA) is an oxidizer widely used for the sterilization of equipment in hospitals, pharmaceutical, cosmetic and food industries and also for water and wastewater disinfection. Even with its increasing applications, there have been no previous theoretical studies that explain the experimental results based on its molecular behavior. In this context, this work used calculations based on the density functional theory (DFT) combined with experimental results to elucidate the decomposition mechanisms of PAA for predicting its stability and the possible products generated from its decomposition. The results obtained showed that the protonation of PAA promoted its spontaneous decomposition in acetic acid and molecular oxygen. The hydrolysis mechanism of PAA in acidic medium indicated that the low energy difference involved in the mechanism's stages is responsible for the equilibrium between PAA and H₂O₂. The structural and electronic comparison of PAA with H₂O₂ showed that the O-O bond length of PAA is longer than that of H₂O₂ and is also weaker, therefore may demonstrate greater efficiency in advanced oxidative processes by photocatalysis.

Advanced Oxidation Process with Peracetic Acid and Fe(II) for Contaminant Degradation

Fe(II) is an excellent promoter for advanced oxidation processes (AOPs) because of its environmental ubiquity and low toxicity. This study is among the first to characterize the reaction of peracetic acid (PAA) with Fe(II) ion and apply the Fe(II)/PAA AOP for degradation of micropollutants. PAA reacts with Fe(II) (k = 1.10 × 10⁵-1.56 × 10⁴ M^-1 s^-1 at pH 3.0-8.1) much more rapidly than H₂O₂ and outperforms the coexistent H₂O₂ for reaction with Fe(II). While PAA alone showed minimal reactivity with methylene blue, naproxen, and bisphenol-A, significant abatement (48-98%) of compounds was observed by Fe(II)/PAA at initial pH of 3.0-8.2. The micropollutant degradation by Fe(II)/PAA exhibited two kinetic phases (very rapid then slow) related to PAA and H₂O₂, respectively. Based on experimental evidence, formation of carbon-centered radicals (CH₃C(O)O^•, CH₃C(O)^•, and ^•CH₃), ^•OH, and Fe(IV) reactive intermediate species from the PAA and Fe(II) reactions in the presence of H₂O₂ is hypothesized. The carbon-centered radicals and/or Fe(IV) likely played an important role in micropollutant degradation in the initial kinetic phase, while ^•OH was important in the second reaction phase. The transformation products of micropollutants showed lower model-predicted toxicity than their parent compounds. This study significantly advances the understanding of PAA and Fe(II) reaction and demonstrates Fe(II)/PAA to be a feasible advanced oxidation technology.

Comparative ecotoxicological evaluation of peracetic acid and the active chlorine of calcium hypochlorite: Use of Dugesia tigrina as a bioindicator of environmental pollution

Chlorine plays a primary role in the disinfection of drinking water and wastewater due to its effectiveness as a biocide; however, there is evidence of the formation of toxic byproducts from its application, and this has promoted the search for alternatives. Alternative disinfectants can be effective in the inactivation of pathogenic microorganisms and are less damaging to human health and aquatic ecosystems. However, more information is needed on the effect of residual concentrations on the environment. This work compares the ecotoxicological effects of PAA disinfectants and the active chlorine of calcium hypochlorite in relation to the organism Dugesia tigrina (planaria), in terms of the acute effects: LC₅₀, and chronic effects: feeding, locomotion, regeneration, reproduction and fertility. The results indicated that the active chlorine was more toxic than PAA, with LC₅₀ (96 h) of 2.63 mg.L^-1 and 3.16 mg.L^-1, respectively. Sub-lethal exposure to active chlorine was more toxic when compared to PAA, and there was evidence of significantly reduced feeding and locomotion, causing a greater delay in regeneration and impairment in reproduction and fertility. The results allowed the comparison of the two disinfectants using half-life constants of the compounds and the lowest observed effect level (LOEC) of the oxidants. Chlorine represents a greater risk to the ecosystem for a longer period. The results obtained in this study can help in the establishment of discharge limits for PAA in water bodies.

Higher functionality of bacterial plasmid DNA in water after peracetic acid disinfection compared with chlorination

Peracetic acid (PAA) is an emerging disinfectant with a low disinfection by-product formation potential, but how PAA destroys gene function after killing bacteria remains to be studied. Bacterial plasmid DNA is a mobile genetic element that often harbors undesirable genes encoding antibiotic resistance and virulence factors. Even though PAA efficiently kills bacteria, bacterial plasmids and other mobile genetic elements might still be intact and functional after PAA disinfection, posing potential public health and environmental risks. This study evaluated the impact of PAA disinfection on the functionality of plasmid DNA in vivo and compared the results with those from chlorination. We delivered a plasmid DNA harboring two antibiotic resistance genes to Escherichia coli TOP10 to form an antibiotic-resistant bacterium (ARB). The planktonic ARB was treated with PAA and chlorine to find the minimum doses inhibiting the regrowth of the strain. PAA and chlorine stopped the regrowth at 8 ± 1 mg PAA·L^-1 and 20 ± 9 mg Cl₂·L^-1, respectively. The functionality of the plasmid DNA after PAA and chlorine disinfection was then determined at higher doses in vivo. Neither PAA nor chlorine completely destroyed the plasmid DNA. However, chlorine was more efficient than PAA in eliminating the plasmid DNA. PAA at 25 mg PAA·L^-1 reduced the transforming activity of the plasmid DNA by less than 0.3 log₁₀ units, whereas chlorine at 25 mg Cl₂·L^-1 reduced the transforming activity by approximately 1.7 log₁₀ units. Chlorine had a more pronounced impact on the functionality of the plasmid DNA because it oxidizes or destroys bacterial components including plasmid DNA faster than PAA. In addition, environmental scanning electron microscopy shows that chlorination desiccated the cells resulting in the flat cellular structure and possibly more complete loss of plasmid DNA, whereas PAA disinfection had a less impact on cell structure and morphology. This study demonstrates that more plasmid DNA remains functional in water after PAA disinfection than after chlorination. These functional genetic elements could be acquired by other microorganisms via horizontal gene transfer to pose potential public health and environmental risks.

Tertiary treatment of urban wastewater by solar and UV-C driven advanced oxidation with peracetic acid: Effect on contaminants of emerging concern and antibiotic resistance

Photo-driven advanced oxidation process (AOP) with peracetic acid (PAA) has been poorly investigated in water and wastewater treatment so far. In the present work its possible use as tertiary treatment of urban wastewater to effectively minimize the release into the environment of contaminants of emerging concern (CECs) and antibiotic-resistant bacteria was investigated. Different initial PAA concentrations, two light sources (sunlight and UV-C) and two different water matrices (groundwater (GW) and wastewater (WW)) were studied. Low PAA doses were found to be effective in the inactivation of antibiotic resistant Escherichia coli (AR E. coli) in GW, with the UV-C process being faster (limit of detection (LOD) achieved for a cumulative energy (Q_UV) of 0.3 kJL^-1 with 0.2 mg PAA L^-1) than solar driven one (LOD achieved at Q_UV = 4.4 kJL^-1 with 0.2 mg PAA L^-1). Really fast inactivation rates of indigenous AR E. coli were also observed in WW. Higher Q_UV and PAA initial doses were necessary to effectively remove the three target CECs (carbamazepine (CBZ), diclofenac and sulfamethoxazole), with CBZ being the more refractory one. In conclusion, photo-driven AOP with PAA can be effectively used as tertiary treatment of urban wastewater but initial PAA dose should be optimized to find the best compromise between target bacteria inactivation and CECs removal as well as to prevent scavenging effect of PAA on hydroxyl radicals because of high PAA concentration.

Inhibition of regrowth of planktonic and biofilm bacteria after peracetic acid disinfection

Peracetic acid (PAA) is a promising alternative to chlorine for disinfection; however, bacterial regrowth after PAA disinfection is poorly understood. This study compared the regrowth of bacteria (Gram-negative Pseudomonas aeruginosa PAO1 and Gram-positive Bacillus sp.) after disinfection with PAA or free chlorine. In the absence of organic matter, PAA and free chlorine prevented the regrowth of planktonic cells of P. aeruginosa PAO1 at C·t (= disinfectant concentration × contact time) doses of (28.5 ± 9.8) mg PAA·min·L^-1 and (22.5 ± 10.6) mg Cl₂·min·L^-1, respectively, suggesting that they had comparable efficiencies in preventing the regrowth of planktonic bacteria. For comparison, the minimum C·t doses of PAA and free chlorine to prevent the regrowth of P. aeruginosa PAO1 biofilm cells in the absence of organic matter were (14,000 ± 1,732) mg PAA·min·L^-1 and (6,500 ± 2,291) mg Cl₂·min·L^-1, respectively. PAA was less effective than free chlorine in killing bacteria within biofilms in the absence of organic matter most likely because PAA reacts with biofilm matrix constituents slower than free chlorine. In the presence of organic matter, although the bactericidal efficiencies of both disinfectants significantly decreased, PAA was less affected due to its slower reaction with organic matter and/or slower self-decomposition. For instance, in a dilute Lysogeny broth-Miller, the minimum concentrations of PAA and free chlorine to prevent the regrowth of planktonic P. aeruginosa PAO1 were 20 mg PAA·L^-1 and 300 mg Cl₂·L^-1, respectively. While both disinfectants are strong oxidants disrupting cell membrane, environmental scanning electron microscopy (ESEM) revealed that PAA made holes in the center of the cells, whereas free chlorine desiccated the cells. Overall, this study shows that PAA is a powerful disinfectant to prevent bacterial regrowth even in the presence of organic matter.

Antimicrobial susceptibility and sessile behaviour of bacteria isolated from a minimally processed vegetables plant

In this study, 20 heterotrophic bacteria from a minimally processed vegetables (MPV) plant were tested for their susceptibilities to five antibiotics (tetracycline, erythromycin, ampicillin, levofloxacin and ciprofloxacin), their (co)aggregation abilities and their survival under gastric simulated conditions. Peracetic acid (PA) and sodium hypochlorite (SH), both at 50 ppm, were evaluated for their abilities to control biofilms of these bacteria. In general, the Gram-negative bacteria were found to be more resistant to the selected antibiotics. Two isolates, Rhanella aquatilis and Stenotrophomonas maltophilia, demonstrated multidrug resistance. Only Rhodococcus erythropolis presented aggregation potential, while no bacterium survived under the gastric conditions. The biofilm experiments showed PA as less efficient than SH in killing biofilms and neither of the disinfectants was able to fully eliminate the biofilms. Significant regrowth was observed for most of the biofilms. The results indicate that alternative and/or complementary disinfection strategies are required to guarantee food safety.