Peracetic Acid Disinfection Research Articles

Evaluation of novel disinfection methods for the remediation of heavily contaminated thermostatic mixing valves and water systems with Pseudomonas aeruginosa biofilm: considerations for new and existing healthcare water systems

Pseudomonas aeruginosa is a leading cause of nosocomial Gram-negative bacteraemia. Water systems are a well-documented source of P.aeruginosa and established biofilms are difficult to remove. To evaluate the efficacy of regular flushing, peracetic acid disinfection, in-tap thermal disinfection, and in-line thermal disinfection to eradicate P.aeruginosa biofilm in a colonized tap model. A simulated tap system was constructed and inoculated with a reference and an environmental strain of P.aeruginosa to form biofilm. Water samples were collected from the taps and P.aeruginosa levels enumerated following disinfection methods. To simulate regular flushing, taps were flushed for 5min, five times per day with water tested daily. Peracetic acid (4000ppm) was manually injected into the system and flushed through the system with a pump. Thermal flushing at 60°C was performed in-line and with an in-tap bypass valve. Tests were conducted with cross-linked polyethylene (PEX) piping and repeated with copper piping. Regular flushing and peracetic acid applied with a pump did not reduce P.aeruginosa levels. A limited reduction was observed when manually injecting peracetic acid. In-tap thermal flushing eradicated P.aeruginosa in copper piping but not PEX. In-line thermal flushing was the most effective at reducing P.aeruginosa levels; however, it did not eradicate the biofilm. In-line thermal flushing was the most effective method to remove P.aeruginosa biofilm. Results vary significantly with the strain of bacteria and the composition of the plumbing. Several methods used in combination may be necessary to remove established biofilm.

Reduction and regrowth of total coliform bacteria, fecal coliform bacteria, and E. coli after chlorine and peracetic acid disinfection in the hospital effluent

Reduction and regrowth of total coliform bacteria, fecal coliform bacteria, and E. coli after chlorine and peracetic acid disinfection in the hospital effluent

Peracetic acid disinfection induces antibiotic-resistant E. coli into VBNC state but ineffectively eliminates the transmission potential of ARGs

The occurrence of a viable but nonculturable (VBNC) state in antibiotic-resistant E. coli (AR E. coli) and inefficient degradation of their antibiotic resistance genes (ARGs) may cause potential health risks during disinfection. Peracetic acid (PAA) is an alternative disinfectant for replacing chlorine-based oxidants in wastewater treatment, and the potential of PAA to induce a VBNC state in AR E. coli and to remove the transformation functionality of ARGs were investigated for the first time. Results show that PAA exhibits excellent performance in inactivating AR E. coli (over 7.0-logs) and persistently inhibiting its regeneration. After PAA disinfection, insignificant changes in the ratio of living to dead cells (∼4%) and the level of cell metabolism, indicating that AR E. coli were induced into VBNC states. Unexpectedly, PAA was found to induce AR E. coli into VBNC state by destroying the proteins containing reactive amino acids at thiol, thioether and imidazole groups, rather than the result of membrane damage, oxidative stress, lipid destruction and DNA disruption in the conventional disinfection processes. Moreover, the result of poor reactivity between PAA and plasmid strands and bases confirmed that PAA hardly reduced the abundance of ARGs and damaged the plasmid's integrity. Transformation assays and real environment validation indicated that PAA-treated AR E. coli could release large abundance of naked ARGs with high-efficiency transformation functionality (∼5.4 × 10–4 - ∼8.3 × 10–6) into the environment. This study has significant environmental implications for assessing the transmission of antimicrobial resistance during PAA disinfection.

Peracetic acid as a disinfectant for wastewater reuse — Regulation (EU) 2020/741 application on a pilot-scale

Water scarcity affects already a large part of the world's population. To overcome this situation, water management is needed, and wastewater reuse must be implemented and included as a new approach. To achieve that objective water quality must comply with the parameters established in the Regulation (EU) 2020/741 of the European Parliament and the Council of the European Union and new treatment solutions have to be developed. The main goal of this pilot study was to evaluate the peracetic acid (PAA) disinfection efficiency in a real wastewater treatment plant (WWTP) in order to accomplish the wastewater reuse objective. To this end, six disinfection conditions were studied, three PAA doses (5, 10, and 15) and three contact times (5, 10, and 15) based on the commonly used disinfection operational conditions in real WWTP. Comparing the Total Suspended Solids (TSS), turbidity, Biological Oxygen Demand (BOD5) and Escherichia coli content, after and before the disinfection step, was possible to conclude that PAA ensures the Regulation (EU) 2020/741 requirements and that the disinfected effluent can be reused for several uses. All the conditions in which the PAA dose was 15 mg/L and the condition with 10 mg/L of PAA with a contact time of 15 min were the most promising, presenting the second highest water quality class achieved. The results of this study illustrate the potential of PAA as an alternative disinfectant for wastewater treatment and, bring it closer to the water reuse objective by presenting several possibilities for water uses.

Selective Transformation of Micropollutants in Saline Wastewater by Peracetic Acid: The Overlooked Brominating Agents.

Peracetic acid (PAA) is an emerging alternative disinfectant for saline waters; HOBr or HOCl is known as the sole species contributing to halogenation reactions during PAA oxidation and disinfection. However, new results herein strongly indicated that the brominating agents (e.g., BrCl, Br2, BrOCl, and Br2O) are generated at concentrations typically lower than HOCl and HOBr but played significant roles in micropollutants transformation. The presence of Cl- and Br- at environmentally relevant levels could greatly accelerate the micropollutants (e.g., 17α-ethinylestraiol (EE2)) transformation by PAA. The kinetic model and quantum chemical calculations collectively indicated that the reactivities of bromine species toward EE2 follow the order of BrCl > Br2 > BrOCl > Br2O > HOBr. In saline waters with elevated Cl- and Br- levels, these overlooked brominating agents influence bromination rates of more nucleophilic constituents of natural organic matter and increase the total organic bromine. Overall, this work refines our knowledge regarding the species-specific reactivity of brominating agents and highlights the critical roles of these agents in micropollutant abatement and disinfection byproduct formation during PAA oxidation and disinfection.

Antibacterial effects of peracetic acid disinfection assessed by culturability, enzyme activity and flow cytometry

Aquaculture water disinfection with around 1 mg/L peracetic acid (PAA) was proved in various studies to effectively impair microbial proliferation and reduce pathogen-caused fish mortality. In the present study, we monitored the antibacterial effect of biweekly water disinfection with 1 mg/L PAA at a local flow-through fish farm for 8 weeks. Results from replicate water samples showed inconsistency of antibacterial efficacy assessed with colony forming units (CFU) of total culturable bacteria and a commercial enzyme activity assay. Single PAA disinfection caused up to 90% reduction of CFU in water. In contrast, the microbial hydrolase activity was hardly affected or even enhanced. Both methods have limitations and can't truly represent viable bacteria. We further monitored the temporal response of two Yersinia ruckeri isolates in suspensions to single PAA disinfection via high-throughput flow cytometry. We found out that the bacterial cell membrane damage appeared not instantly but with a lag phase of at least 2 h post disinfection at 4 °C. The abundance of cell membrane damage, considered as cumulative bacterial mortality, kept rising and maximized at 48 h post disinfection. The survived cells were more likely to enter the viable but non-culturable (VBNC) state at higher PAA concentrations. One isolate was more prone to enter the VBNC state than the other. Neither Y. ruckeri isolate showed measurable reaction with the enzyme substrate of the commercial microbial hydrolase activity assay. Our findings refresh knowledge about the dynamics of bacterial cell mortality post PAA disinfection (probably also similar non-thermal disinfection methods). Aquaculture practice should be aware of the delayed disinfection outcomes and pay attention to the dominance of VBNC state.

Insights into the oxidation of bisphenol A by peracetic acid enhanced with bromide: The role of free bromine

Peracetic acid (PAA) has received great attention in wastewater treatment as an alternative to free chlorine. However, wastewater constituents such as bromide (Br−) may affect the PAA-based oxidation process. In this study, we reported a detailed kinetic and mechanistic study on bisphenol A (BPA, 20 μM) oxidation by PAA in the presence of Br−. When the concentration of Br− was increased from 20 to 100 μM, the removal rate of BPA was significantly increased, which was attributed to the formation of secondary oxidant hypobromous acid. When BPA was treated with 5 mM PAA in the presence of 100 µM Br− at pH 7.0, ∼26 % of bromide was converted into organic bromine in 24 h. Brominated disinfection byproducts (Br-DBPs) accounted for ∼8.2 % of total organic bromine generated, among them the concentrations of bromoform (CHBr3), dibromoacetic acid (DBAA), and tribromoacetic acid (TBAA), were determined to be 0.94, 0.99, and 0.21 µM, respectively. A total of 23 transformation products were identified by high-resolution mass spectrometry (HRMS) analyses. Three transformation pathways, including CC (C1-C2 and C2-C4) bridge bond cleavage, phenyl ring bromination, and stepwise oxidation were proposed and rationalized by theoretical calculations. In conclusion, the presence of Br− can enhance the degradation efficiency of BPA in the PAA disinfection process; however, the formation of potentially carcinogenic brominated intermediates in Br−-containing wastewaters should be scrutinized.

Disinfection efficiency prediction under dynamic conditions: Application to peracetic acid disinfection of wastewater

In this work, a mechanistic dynamic model of continuous flow peracetic acid (PAA) disinfection was developed, calibrated and validated, assuming E. coli as indicator microorganism. The model was conceived as a 1-dimensional dispersion model integrating PAA first order decay and E. coli inactivation rate. Lab-scale batch experiments of PAA decay and E. coli inactivation experiments were performed to calibrate corresponding kinetic models. In each sample, conventional wastewater quality parameters were monitored. A PAA pilot reactor was set up to perform both tracer studies, for dispersion model calibration, and continuous flow disinfection experiments, to validate the integration of hydraulics and kinetics models, under both stationary and dynamic conditions. Linear regression models were calibrated to predict hydrodynamic dispersion, given the flow rate, and PAA decay parameters, given effluent quality and PAA dosage. Successful validation of the PAA disinfection model proved the importance of (i) considering the disinfection process as a dynamic system and (ii) integrating real-time estimation of process disturbances, being the initial E. coli concentration and the impact of effluent quality and PAA dosage on PAA decay kinetics. Importantly, novel inactivation models were proposed, as two different modifications of a literature model for thermal inactivation. These models are suitable for dynamic simulation of Eulerian models and can describe the typical triphasic behavior of inactivation kinetics.

Effective inactivation of fungal spores by the combined UV/PAA: Synergistic effect and mechanisms

Peracetic acid (PAA) can effectively inactivate fungi in water, while may pose a potential risk of regrowth after disinfection. The inactivation kinetic and mechanism of fungal spores by combined UV and PAA (UV/PAA) was investigated in this study. The results showed that synergistic factor of the inactivation of A. niger and A. flavus was 1.44 and 1.37, which indicated significant synergistic effect of UV/PAA. The k of A. niger and A. flavus was similar at pH 5.0 and 7.0, while decreased 60.00% and 39.13% at pH 9.0 compared with that at pH 7.0. The effect of HA concentration on the inactivation efficiency of fungal spores by UV/PAA was negative, while the effect of PAA concentration was positive. The membrane permeabilized cell of A. niger and A. flavus caused by UV/PAA was 17.0% and 31.7%, which was higher than that caused by PAA and UV alone. The changes of morphology of fungal spores and the leakage of intracellular material indicated that the damage of cell structure caused by UV/PAA system was more serious than that of UV or PAA alone. In addition, the four parts that contributed in UV/PAA system was in the following order: UV > radical > PAA > synergistic effect. The inactivation efficiency of combined UV and chlorine (UV/Cl2) was higher than that of UV/PAA. Furthermore, the typical order of the inactivation efficiency in different matrix was: phosphate buffer solution > surface water > secondary effluent. The regrowth potential of fungal spores after UV/PAA treatment was significantly lower than that by PAA alone, indicating that UV/PAA could decrease the microbial regrowth potential after PAA disinfection alone.

Disinfection kinetics of peracetic acid inactivation of pathogenic bacteria in water

Peracetic acid (PAA) has broad application in disinfection, since it produces fewer disinfection by-products. In this study, PAA was used as a disinfectant to inactivate Escherichia coli, Staphylococcus aureus, and Bacillus subtilis under different pHs and turbidity. The effects of different environmental factors on PAA disinfection were compared. The results were fitted by the common disinfection kinetic models, and the CTs were finally calculated according to the disinfectant decay models and the optimal disinfection kinetic models. By comparing PAA with other common disinfectants, the projected application of PAA was discussed.

Unexpected Role of Nitrite in Promoting Transformation of Sulfonamide Antibiotics by Peracetic Acid: Reactive Nitrogen Species Contribution and Harmful Disinfection Byproduct Formation Potential

Peracetic acid (PAA) is an emerging oxidant and disinfectant for wastewater (WW) treatment due to limited harmful disinfection byproduct (DBP) formation. Nitrite (NO2-) is a ubiquitous anion in water, but the impact of NO2- on PAA oxidation and disinfection has been largely overlooked. This work found for the first time that NO2- could significantly promote the oxidation of sulfonamide antibiotics (SAs) by PAA. Unexpectedly, the reactive nitrogen species (RNS), for example, peroxynitrite (ONOO-), rather than conventional organic radicals (R-O•) or reactive oxygen species (ROS), played major roles in SAs degradation. A kinetic model based on first-principles was developed to elucidate the reaction mechanism and simulate reaction kinetics of the PAA/NO2- process. Structural activity assessment and quantum chemical calculations showed that RNS tended to react with an aromatic amine group, resulting in more conversion of NO2--N to organic-N. The formation of nitrated and nitrosated byproducts and the enhancement of trichloronitromethane formation potential might be a prevalent problem in the PAA/NO2- process. This study provides new insights into the reaction of PAA with NO2- and sheds light on the potential risks of PAA in WW treatment in the presence of NO2-.

Effect of water hardness/alkalinity and humic substances on the toxicity of peracetic acid to zebrafish embryos and pathogenic isolates

The prophylactic use of peracetic acid (PAA)-based disinfectants is becoming more popular in aquaculture due to rising concerns regarding sustainability, fish welfare and food safety. However, specific and effective PAA dosing protocols have not been developed to guide the aquaculture industry under diverse production conditions. In the present study, the effect of water hardness/alkalinity and humic substances (HS) on the toxicity of PAA to zebrafish Danio rerio embryos and the efficacy of PAA against the in vitro growth of Yersinia ruckeri and Saprolegnia parasitica was investigated. PAA concentrations that were safe to fish embryos demonstrated strong bactericidal, but limited fungistatic properties. In higher hardness/alkalinity water, or when HS was added, the same concentration of PAA resulted in a smaller pH decrease accompanied by a smaller increase of oxidation-reduction potential (ORP), and showed lower toxicity and weaker antimicrobial effects than in lower hardness/alkalinity waters. We suggest the determining factor of PAA toxicity and its antimicrobial capacity was likely ORP. At low hardness/alkalinity conditions, strong pH reduction (resulting in pH<5) was the dominant role in PAA toxicity to D. rerio embryos. In aquaculture settings, lower PAA doses should be used under lower hardness/alkalinity conditions. Addition of HS under lower hardness/alkalinity conditions can assist with reducing toxicity and the risk to fish. Finally, we determined that repeated PAA disinfection is necessary to achieve a sustained prophylaxis, and we caution that the instant formation of aggregates by HS at high hardness conditions and the subsequent attachment of bacteria may reduce their susceptibility to PAA disinfection.

Differences in chlorine and peracetic acid disinfection kinetics of Enterococcus faecalis and Escherichia fergusonii and their susceptible strains based on gene expressions and genomics

This study was conducted to investigate mechanisms of cross-resistance to chlorine and peracetic acid (PAA) disinfectants by antibiotic-resistant bacteria. Our study evaluated chlorine and PAA based disinfection kinetics of erythromycin-resistant Enterococcus faecalis, meropenem-resistant Escherichia fergusonii, and susceptible strains of these species. Using the integrated second-order disinfectant decay model and first-order Chick-Watson's Law, it was found that the meropenem-resistant Escherichia fergusonii strain showed significantly less log inactivation compared to the susceptible E. fergusonii strain in response to both chlorine and PAA disinfection (p-value = 0.059, 3.5 × 10−6). On the other hand, the susceptible Enterococcus faecalis strain showed similar log inactivation compared to the erythromycin-resistant strain in response to either treatment (p-value = 0.075, 0.28). Meropenem-resistant E. fergusonii showed an increase in gene expression of New Delhi metallo-β-lactamase (blaNDM-1) gene to chlorine, but there was no increase in expression to PAA. Whole genome sequencing (WGS) was then conducted to elucidate the differences in genes among both resistant and susceptible table E. fergusonii strains. The average nucleotide identity (ANI) analysis of the draft genomes (>97% similarity) suggests that meropenem-resistant E. fergusonii (S1) and meropenem-susceptible E. fergusonii (S2) are the same species but different strains. Both strains have the same genes for oxidative stress pathways, oxidative scavenger genes, and nearly 40 different antibiotic efflux pump genes. The chromosomal and plasmid draft genomes of meropenem-resistant and susceptible E. fergusonii strains each have 65 and 52 antibiotic resistance genes, respectively. Of these, the resistant E. fergusonii strain harbored the extended-spectrum beta-lactamases blaCTX-M-15 and blaTEM-1 genes located on the chromosome, and a blaTEM-1 gene on the plasmid. The overall findings of this study are significant, as they reveal that antibiotic-resistant and susceptible strains of E. fergusonii exhibit different responses towards chlorine and PAA disinfection.

Comparative analysis of peracetic acid (PAA) and permaleic acid (PMA) in disinfection processes

The growing demand to reduce chlorine usage and control disinfection byproducts increased the development of new strategies in wastewater treatments. Organic peracids are increasingly attracting interest in disinfection activities as a promising alternative to chlorine and chlorine-based agents. In this study, we assessed the antimicrobial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) of a new organic peracid, permaleic acid (PMA) compared with the reference peracetic acid (PAA). Disinfectant properties were evaluated by i) disk diffusion agar, ii) broth microdilution, iii) antibiofilm properties. PMA demonstrated a 10- and 5-fold decrease in the microbial inhibitory concentration (MIC) value against E. coli and S. aureus respectively, compared to PAA. Results showed greater efficacy of PMA regarding wastewater (WW) and treated wastewater (TWW) disinfection at low concentrations. Furthermore, the biofilm degradation ability was only observed following PMA treatment, for both strains. Bacterial regrowth from biofilm matrix after PAA and PMA disinfection, in the absence and presence of organic matter, was evaluated. PMA was more efficient than PAA to prevent the regrowth of planktonic cells of S. aureus and E. coli. After PAA and PMA treatment, in the presence of organic matter, the bacterial regrowth inhibition was maintained up to 10 and 5 g/L, respectively. Based on these results, PMA could be used as a valid alternative to the currently used disinfection methods.

Simultaneous inactivation of multidrug-resistant Escherichia coli and enterococci by peracetic acid in urban wastewater: Exposure-based kinetics and comparison with chlorine

The presence of antibiotic resistance in wastewater sparked a great interest in investigating the inactivation of antibiotic-resistant bacteria by disinfecting agents. In this study, the inactivation kinetics of multidrug-resistant E. coli and enterococci by an emerging environmentally-friendly disinfectant, peracetic acid (PAA), in wastewater and phosphate buffer at pH 6.5 and pH 7.5, were characterized. It was demonstrated that the inactivation of the studied multidrug-resistant bacteria was governed by their exposure to PAA, i.e., integral of the PAA concentration over time (integral CT or ICT). Both regimes of the PAA inactivation of bacteria, i.e., initial resistance followed by a faster inactivation, were described well by an ICT-based Chick-Watson inactivation kinetic model. In wastewater at pH 7.5, the model-predicted ICT requirements showed that the multidrug-resistant enterococci were less susceptible to PAA than E. coli, e.g., to achieve a 3-log reduction, an ICT of 32.7 mg min/L and 23.4 mg min/L was needed, respectively. No regrowth of the studied bacteria was observed after 72 h from PAA disinfection at 25 ± 1 °C. Soluble constituents of wastewater decreased the PAA inactivation of both multidrug-resistant bacteria, i.e., higher inactivation was observed in phosphate buffer than wastewater at the same pH of 7.5. In phosphate buffer, a lower pH of 6.5 resulted in higher inactivation of multidrug-resistant E. coli compared with pH 7.5, but it did not affect the PAA inactivation of multidrug-resistant enterococci. A comparison with the most commonly used chemical disinfectant, chlorine, showed higher inactivation of both multidrug-resistant bacteria by chlorine and higher chlorine decay than PAA. The results of the present study may have implications in designing a PAA disinfection process, aiming at controlling antibiotic resistance, in terms of selecting a suitable fecal indicator and optimizing disinfectant dosing.

Peracetic Acid Sanitation on Arugula Microgreens Contaminated with Surface-Attached and Internalized Tulane Virus and Rotavirus.

Hydroponic production of vegetables is becoming more common, especially in regions with unfavorable climate for year-round crop production. However, if viruses are present in the hydroponics feed water, then there is a chance that infectious viruses will be internalized into the tissues of hydroponically grown vegetables. When this happens, surface sanitization of postharvest vegetables may not be effective because the sanitizer cannot disinfect the internalized viruses. In this study, we determined if the effectiveness of peracetic acid (PAA), a sanitizer used in the vegetable industry, is affected by the location of viruses (produce surface or interior tissue) in microgreen arugula. Either internally or externally contaminated hydroponically grown microgreen arugula was then treated with PAA at either 30 or 80ppm for up to 3min. The PAA disinfection efficacy was higher when the RV was on the arugula surface (approximately 5-log10 in PFU after 3min of exposure), instead of the arugula interior (1.5-log10 in PFU after 3min of exposure). However, PAA disinfection efficacy of TV was not dependent on the virus location in arugula. For both internalized TV and RV, the disinfection efficacy was less than 2-log10 in PFU using all the tested PAA concentrations and exposure times examined here. Thus, both the type and location of virus in fresh vegetables may influence the virus disinfection of postharvest vegetables. Therefore, the optimization of sanitation for postharvest fresh vegetables is needed to reduce foodborne viral infection risks.

Study on the Efficacy of Peracetic Acid Disinfectant (Type III) on Gastrointestinal Endoscopy Disinfection.

Purpose:The purpose of this study was to evaluate the disinfection efficacy of peracetic acid disinfectant (Type III) on gastrointestinal endoscopy.Methods:Endoscopes were disinfected, respectively, by 2% glutaraldehyde and peracetic acid disinfectant (Type III) according to the procedures stipulated by the 2016 version of “Regulation for cleaning and disinfection technique of flexible endoscope,” then samples were collected through biopsy channel at the specified steps. The bacterial count and pathogenic bacteria of these samples were detected, and hepatitis B virus surface antigen, hepatitis C virus antibody, and Treponemiapallidum antibody were detected by chemiluminescent microparticle immunoassay in peracetic acid disinfectant (Type III) group. The samples from the peracetic acid disinfectant (Type III) group were collected for 5 days continuously.Results:In total, 56 gastroscopes and 16 colonoscopes were disinfected by 2% glutaraldehyde (GA Group), 46 gastroscopes, and 15 colonoscopes were disinfected by peracetic acid disinfectant (Type Ⅲ) (PAA Group). After disinfection, the bacterial count was significantly reduced in the 2 groups (P<0.05). In terms of the qualified rate of gastroscopes and total qualified rate, the PAA Group was better than GA Group [the qualified rate of gastroscopes: 97.83% (45/46) vs. 92.86% (52/56), P>0.05; total qualified rate: 98.36% (60/61) vs. 94.44% (68/72), P>0.05], the qualified rate of colonoscopes in the 2 groups were both 100.00% (15/15, 16/16). After disinfecting by peracetic acid disinfectant (Type Ⅲ), hepatitis B virus surface antigen, anti-hepatitis C virus, and Treponemiapallidum antibody were negative. In term of colonies number detected for 5 days continuously, there was no significant difference at different collection steps (P>0.05).Conclusions:Peracetic acid disinfectant (Type III) can be well applied to clinical with meeting the standard of high-level disinfection for gastrointestinal endoscopy, and after disinfecting by peracetic acid disinfectant (Type III), there was no obvious bacterial residue in the biopsy channel.

Comparison of UV, Peracetic Acid and Sodium Hypochlorite Treatment in the Disinfection of Urban Wastewater.

One source of water contamination is the release of wastewater that has not undergone efficient treatment. The aim of this study was to evaluate the reduction obtained with sodium hypochlorite (NaClO), UV and peracetic acid disinfection treatment of Salmonella spp., pathogenic Campylobacter, STEC and bacterial indicators in three full-scale municipal wastewater plants. A general reduction in Salmonella was observed after disinfection, but these bacteria were detected in one UV-treated sample (culture method) and in 33%, 50% and 17% of samples collected after NaClO, UV and PAA disinfection treatments, respectively (PCR method). A better reduction was also observed under NaClO disinfection for the microbial indicators. Independent of the disinfection treatment, E. coli O157:H7 was not detected in the disinfected samples, whereas some samples treated with UV and PAA showed the presence of the stx1 gene. No reduction in the presence of stx2 genes was verified for any of the disinfection treatments. Campylobacter was not detected in any of the analysed samples. The overall results highlight a better reduction in microbiological parameters with a NaClO disinfection treatment in a full-scale municipal wastewater plant compared with UV and PAA. However, the results indicate that a complete and specific monitoring program is necessary to prevent a possible risk to public health.

Interactions between peracetic acid and TiO2 nanoparticle in wastewater disinfection: Mechanisms and implications

While peracetic acid (PAA) are known to be susceptible to decomposition by metals for radical generation, herein we report a novel decomposition process of PAA with TiO2 nanoparticle (nTiO2) for the first time. nTiO2 in anatase (A_nTiO2) could significantly enhance the decomposition of PAA, whereas, nTiO2 in rutile phase had no impact on the stability of PAA. Electron paramagnetic resonance (EPR) technique and a radical quenching study indicated lack of involvement of reactive radicals. In-depth investigation revealed that the {001} facets of A_nTiO2 with high surface free energy were especially reactive for the catalytic decomposition of PAA. Theoretical calculations proved the adsorption of PAA onto A_nTiO2 {001} surface was much more favorable than the predominated {101} facets. The unsaturated five coordinated Ti (Ti5c), typical Lewis acid sites on A_nTiO2 {001} surface, were further confirmed as the dominant active sites for catalyzing PAA decomposition. This novel decomposition process could enhance the stability and migration of A_nTiO2, increasing the potential environmental risk. Meanwhile, the disinfection of PAA was inhibited by introducing A_nTiO2. The new findings of this study broaden the knowledge on PAA decomposition process, and have an important implication for PAA disinfection and environmental behavior of TiO2 nanoparticle.

Soft sensor predictor of E. coli concentration based on conventional monitoring parameters for wastewater disinfection control

Real-time acquisition of indicator bacteria concentration at the inlet of disinfection unit is a fundamental support to the control of chemical and ultraviolet wastewater disinfection. Culture-based enumeration methods need time-consuming laboratory analyses, which give results after several hours or days, while newest biosensors rarely provide information about specific strains and outputs are not directly comparable with regulatory limits as a consequence of measurement principles.In this work, a novel soft sensor approach for virtual real-time monitoring of E. coli concentration is proposed. Conventional wastewater physical and chemical indicators (chemical oxygen demand, total nitrogen, nitrate, ammonia, total suspended solids, conductivity, pH, turbidity and absorbance at 254 nm) and flowrate were studied as potential predictors of E. coli concentration relying on data collected from three full-scale wastewater treatment plants. Different methods were compared: (i) linear modeling via ordinary least squares; (ii) ridge regression; (iii) principal component regression and partial least squares; (iv) non-linear modeling through artificial neural networks.Linear soft sensors reached some degree of accuracy, but performances of the artificial neural network based models were by far superior. Sensitivity analysis allowed to prioritize the importance of each predictor and to highlight the site-specific nature of the approach, because of the site-specific nature of relationships between predictors and E. coli concentration. In one case study, pH and conductivity worked as good proxy variables when the occurrence of intense rain events caused sharp increases in E. coli concentration. Differently, in other case studies, chemical oxygen demand, total suspended solids, turbidity and absorbance at 254 nm accounted for the positive correlation between low wastewater quality and E. coli concentration. Moreover, sensitivity analysis of artificial neural network models highlighted the importance of interactions among predictors, contributing to 25 to 30% of the model output variance. This evidence, along with performance results, supported the idea that nonlinear families of models should be preferred in the estimation of E. coli concentration.The artificial neural network based soft sensor deployment for control of peracetic acid disinfectant dosage was simulated over a realistic scenario of wastewater quality recorded by on-line sensors over 2 months. The scenario simulations highlighted the significant benefit of an E. coli soft sensor, which provided up to 57% of disinfectant saving.