Evaluation of the efficiency of peracetic acid in the disinfection of sewage effluents

Influence of peroxyacetic acid concentration, temperature, pH, and treatment time on antimicrobial efficacy against Salmonella on chicken wings

Peroxyacetic acid (PAA) is commonly used during poultry processing to reduce the prevalence of Salmonella on carcasses and parts. Wash solutions containing PAA are used at varying concentrations during processing and processors use internally validated practices that best suit the needs of the individual establishment. This study was conducted to determine how temperature, pH, and contact time in combination with PAA concentration can affect the survival of Salmonella on poultry. The effectiveness of PAA in reducing the population of Salmonella on chicken wings was dependent on the concentration and temperature of the PAA solutions. The pH or contact time had no effects (P > 0.05) on total Salmonella or Salmonella Infantis reduction (log CFU/mL). Treatment with 0 ppm PAA at 27°C did not reduce (P > 0.05) total Salmonella or Salmonella Infantis compared to the inoculated, untreated control; in contrast, treatment at 4°C and 0 ppm PAA reduced (P < 0.05) total Salmonella and Salmonella Infantis. Treatments applied at 4°C significantly reduced (P < 0.05) total Salmonella at 50, 200, and 500 ppm PAA, compared to treatment at 27°C among the same PAA concentration. The population of Salmonella Infantis was significantly reduced (P < 0.05) at 4°C with 0, 50, 200, 500, and 1,000 ppm PAA among the same PAA concentration, compared to treatment at 27°C. Treatment conditions, such as temperature, can impact the effectiveness of PAA used as an antimicrobial treatment during poultry processing, and the results from this study can provide useful insights that could assist poultry processors to effectively incorporate PAA into antimicrobial intervention systems.

The temperature-dependent kinetics and bacteria regrowth by performic acid and sodium hypochlorite disinfection

Sodium hypochlorite (NaOCl) has been widely used as a disinfectant in water and wastewater treatment, because of its high efficiency and low cost, whereas the bio-toxicity of its disinfection byproducts (DBPs) raised great concern. Performic acid (PFA) produces less DBPs and shows strong oxidation abilities. In this study, the effect of temperature on NaOCl and PFA disinfection as well as bacteria regrowth were evaluated. First, the inactivation of Escherichia coli, Staphylococcus aureus, and Bacillus subtilis by NaOCl and PFA at 4 and 20 °C, detected by cell cultured-based plate counting were fitted to kinetic models, and the predicted CTs were calculated. The results showed that NaOCl was more effective than PFA for E. coli and S. aureus inactivation, and the temperature was positively correlated to disinfection. Second, bacteria regrowth was evaluated at different temperatures (4 and 20 °C) of disinfection and storage. The results showed that the bacteria inactivated by NaOCl regrew prominently, especially for those inactivated at 4 and stored at 4 °C, probably through the mechanism of reactivation of viable but non-culturable (VBNC) bacteria. PFA was superior in suppressing bacteria regrowth, and it may be used as an alternate disinfectant in water treatment in cold environment.

Inactivation methods for human coronavirus 229E on various food-contact surfaces and foods

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of the COVID-19 outbreaks, is transmitted by respiratory droplets and has become a life-threatening viral pandemic worldwide. The aim of this study was to evaluate the effects of different chemical (chlorine dioxide [ClO₂] and peroxyacetic acid [PAA]) and physical (ultraviolet [UV]-C irradiation) inactivation methods on various food-contact surfaces (stainless steel [SS] and polypropylene [PP]) and foods (lettuce, chicken breast, and salmon) contaminated with human coronavirus 229E (HCoV-229E). Treatments with the maximum concentration of ClO₂ (500 ppm) and PAA (200 ppm) for 5 min achieved >99.9% inactivation on SS and PP. At 200 ppm ClO₂ for 1 min on lettuce, chicken breast, and salmon, the HCoV-229E titers were 1.19, 3.54, and 3.97 log₁₀ TCID₅₀/mL, respectively. Exposure (5 min) to 80 ppm PAA achieved 1.68 log₁₀ reduction on lettuce, and 2.03 and 1.43 log₁₀ reductions on chicken breast and salmon, respectively, treated with 1500 ppm PAA. In the carrier tests, HCoV-229E titers on food-contact surfaces were significantly decreased (p < 0.05) with increased doses of UV-C (0–60 mJ/cm²) and not detected at the maximum UV-C dose (Detection limit: 1.0 log₁₀ TCID₅₀/coupon). The UV-C dose of 900 mJ/cm² proved more effective on chicken breast (>2 log₁₀ reduction) than on lettuce and salmon (>1 log₁₀ reduction). However, there were no quality changes (p > 0.05) in food samples after inactivation treatments except the maximum PAA concentration (5 min) and the UV-C dose (1800 mJ/cm²).

Examining the antimicrobial efficacy of granulated tetraacetylethylenediamine derived peracetic acid and commercial peracetic acid in urban wastewaters

The ever-increasing need for access to safe water has meant that alternative water sources and innovative water reclamation approaches are often required to meet the global water demand. As a result, many wastewater treatment facilities have faced regulatory pressure to seek alternative disinfection methods that ensure public health safety, while adhering to regulations that set limits on carcinogenic disinfection by-products (DBPs). Peracetic acid (PAA) is an emerging wastewater disinfectant in the United States that has been widely used in other industries such as food sanitization and does not produce carcinogenic DBPs. However, several factors such as transport, storage, and physical and chemical effects have stymied its widespread use in wastewater markets. Therefore, the purpose of this study was to examine the antimicrobial efficacy of an on-site generated PAA compared against a commercially available PAA. Antimicrobial efficacy was assessed using standard fecal contamination indicators (i.e., total coliforms and Escherichia coli) in six urban wastewater treatment facilities ranging in size and treatment processes. Overall, few statistical differences were found between the antimicrobial efficacies of on-site generated PAA and commercially available PAA; however, before becoming more widely utilized, the on-site PAA should be tested against emerging fecal contamination indicators (e.g., human norovirus and enterovirus) and be assessed in terms of economic and sustainability impacts. PRACTITIONER POINTS: Alternative Ct approaches should be considered when using disinfectants like PAA. On-site generated PAA can achieve the same level of disinfection as commercial PAA. On-site generation of PAA may help further its use as a wastewater disinfectant.

Intermittent administration of peracetic acid is a mild environmental stressor that elicits mucosal and systemic adaptive responses from Atlantic salmon post-smolts

Background

Fish encounter oxidative stress several times during their lifetime, and it has a pervasive influence on their health and welfare. One of the triggers of oxidative stress in fish farming is the use of oxidative disinfectants to improve rearing conditions, especially in production systems employing recirculation technology. Here we report the physiological and morphological adaptive responses of Atlantic salmon (Salmo salar L.) post-smolts to intermittent exposure to a potent oxidative agent peracetic acid (PAA). Fish reared in semi-commercial scale brackish water recirculating aquaculture system (RAS) were exposed to 1 ppm PAA every 3 days over 6 weeks. Mucosal and systemic responses were profiled before exposure, 22 and 45 days during the intermittent PAA administration.

Results

Oxidative stress was likely triggered as plasma antioxidant capacity increased significantly during the exposure period. Adaptive stress response to the periodic oxidant challenge was likewise demonstrated in the changes in plasma glucose and lactate levels. PAA-induced alterations in the transcription of antioxidants, cytokines, heat shock proteins and mucin genes showed a tissue-specific pattern: downregulation was observed in the gills and olfactory rosette, upregulation occurred in the skin, and no substantial changes in the liver. Further, PAA exposure resulted in histological changes in key mucosal organs (i.e. olfactory rosette, skin and gills); pathological alterations were predominant in the gills where cases of epithelial lifting, hypertrophy and clubbing were prevalent. In addition, intermittent PAA administration resulted in an apparent overproduction of mucus in the nasal mucosa. Lastly, PAA did not dramatically alter the ability of salmon to mount a physiological stress response in the presence of a secondary stressor, though some subtle interference was documented in the kinetics and magnitude of plasma cortisol and glucose response post-stress.

Conclusions

The present study collectively demonstrated that intermittent oxidant exposure was a mild environmental stressor that salmon could mount strong adaptive responses at systemic and mucosal levels. The results will be valuable in optimising the rearing conditions of post-smolts in RAS, especially in adopting water treatment strategies that do not considerably interfere with fish health and welfare.

Comparison of virucidal efficacy of sodium hypochlorite, chlorine dioxide, peracetic acid, and ethanol against hepatitis A virus by carrier and suspension tests

A carrier (stainless steel disc as a default carrier) testing method is very needed for use in the actual food-processing fields by following the standard guideline. Here, we aimed to compare the virucidal efficacy of four commercial liquid disinfectants, including sodium hypochlorite (NaOCl), chlorine dioxide (ClO₂), and peracetic acid (PAA) against hepatitis A virus (HAV) following the OECD guideline protocol based on the quantitative carrier testing method and compared carrier testing results with the suspension testing results. The OECD method specifies a test for establishing whether a chemical disinfectant or a microbicide has a virucidal activity on hard non-porous surfaces. The antiviral efficacy was evaluated by plaque assays, and disinfectants were considered effective if the virus reduction was greater than or equal to 3 log₁₀ (99.9% decrease) for carrier or 4 log₁₀ (99.99% decrease) for suspension tests. Results indicated that ClO₂ above 500 ppm and 50% ethanol were effective in the carrier test method. In contrast, more than 200 ppm NaOCl and 50 ppm ClO₂ for all exposure times and 70% ethanol with contact for more than 5 min were effective in suspension tests. Treatment with PAA (80-2500 ppm) were not effective in carrier or suspension tests. Therefore, we recommend the use of more than 500 ppm ClO₂ or 50% ethanol with exposure for 10 min to disinfect surfaces that may be contaminated with HAV. Thus, these results could be effective in establishing official antiviral efficacy testing methods and basic data.

Effect of caprylic acid alone or in combination with peracetic acid against multidrug-resistant Salmonella Heidelberg on chicken drumsticks in a soft scalding temperature-time setup

The antimicrobial efficacy of caprylic acid (CA), a medium-chain fatty acid, against multidrug-resistant Salmonella Heidelberg (MDR SH) on chicken drumsticks in a soft-scalding temperature-time setup was investigated. Based on the standardization experiments in nutrient media and on chicken breast fillet portions, intact chicken drumsticks were spot inoculated with MDR SH and immersed in water with or without antimicrobial treatments at 54°C for 2 min. The treatments included 0.5% CA, 1% CA, 0.05% peracetic acid (PAA), 0.5% CA + 0.05% PAA, and 1.0% CA + 0.05% PAA. Additionally, the efficacy of the potential scald treatments against MDR SH survival on drumsticks for a storage period of 48 h at 4°C was determined. Furthermore, the effect of these treatments on the surface color of the drumsticks was also evaluated. Appropriate controls were included for statistical comparisons. The antimicrobial treatments resulted in a significant reduction of MDR SH on drumsticks. For the lower inoculum (∼2.5 log₁₀ CFU/g) experiments, 0.5% CA, 1% CA, 0.05% PAA, 0.5% CA + 0.05% PAA, and 1.0% CA + 0.05% PAA resulted in 0.7-, 1.0-, 2.5-, 1.4-, and 1.5- log₁₀ CFU/g reduction of MDR SH on drumsticks, respectively (P < 0.05). The same treatments resulted in 0.9-, 1.3-, 2.5-, 2.2-, and 2.6- log₁₀ CFU/g reduction of MDR SH when the drumsticks were contaminated with a higher inoculum (∼4.5 log₁₀ CFU/g) level (P < 0.05). Moreover, the antimicrobial treatments inactivated MDR SH in the treatment water to undetectable levels, whereas 2.0- to 4.0- log₁₀ CFU/mL MDR SH survived in the positive controls (P < 0.05). Also, the treatments were effective in inhibiting MDR SH on the drumsticks compared to the respective controls during a storage period of 48 h at 4°C; however, the magnitude of reduction remained the same as observed during the treatment (P < 0.05). Additionally, none of the treatments affected the color of the drumsticks (P > 0.05). Results indicate that CA could be an effective natural processing aid against MDR SH on chicken products.

Mechanistic modeling of peracetic acid wastewater disinfection using computational fluid dynamics: Integrating solids settling with microbial inactivation kinetics

While the impact of suspended solids on chemical disinfection kinetics has been widely recognized, a detailed modeling framework for assessing their contribution on disinfection efficiency in municipal contact tanks is yet unavailable. In this paper, we conducted experimental and modeling studies to mechanistically describe the interplay between suspended solids (not removed by gravity settling in secondary clarifiers) and disinfection performance of an emerging disinfectant, peracetic acid, operated in a municipal contact tank. Specifically, we developed an integrated computational fluid dynamics (CFD) model to simultaneously predict the fate and transport of suspended solids, Escherichia coli and peracetic acid in a hypothetical reactor using an exposure-based (i.e., CT-based) inactivation rate expression. The integrated CFD model, calibrated against laboratory data, was used to gain insights on the vertical distribution and local PAA decay effect associated with solids settling and their impact on disinfectant decay and microbial inactivation. Results indicated that: (a) solids settling in contact tanks is a significant phenomenon that cannot be neglected, which can substantially impact disinfection efficiency under low flow conditions; (b) vertical solids distribution and stratification in contact tanks can strongly affect Escherichia coli inactivation by peracetic acid, as highlighted by the CFD modeling studies; (c) Escherichia coli settling is experimentally measurable, and strongly correlated with solids settling. These phenomena can be successfully integrated into a CFD model to obtain a comprehensive description of the PAA disinfection process in presence of changes in secondary effluent quality and flow, a situation typically encountered in municipal contact tanks operated in full scale wastewater treatment plants.

Ultrafiltration Process in Disinfection and Advanced Treatment of Tertiary Treated Wastewater

The paper presents the results of research on the use of ultrafiltration, using membranes of 200 and 400 kDa separation, for disinfection of municipal treated wastewater. The research was conducted on a fractional technical scale using real municipal treated wastewater from two large wastewater treatment plants treating most of the wastewater over the one-million polycentric Gdańsk agglomeration (1.2 million inhabitants). UF 200 kDa and UF 400 kDa processes enabled further improvement of the physical and chemical parameters of treated wastewater. Total phosphorus (to below 0.2 mg/L–UF 200 kDa, 0.13 mg/L–UF 400 kDa) and turbid substances (to below 0.2 mg/L, both membranes) were removed in the highest degree. COD was reduced efficiently (to below 25.6 mgO₂/L–UF 200 kDa, 26.8 mgO₂/L–UF 400 kDa), while total nitrogen was removed to a small extent (to 7.12 mg/L–UF 200 kDa and 5.7 mg/L–UF 400 kDa. Based on the reduction of indicator bacteria; fecal coliforms including E. coli (FC) and fecal enterococci (FE) it was found that the ultrafiltration is an effective method of disinfection. Not much indicator bacterial were observed in the permeate after processes (UF 200 kDa; FC—5 CFU/L; FE—1 CFU/L and UF 400 kDa; FC—70 CFU/L; FE—10 CFU/L. However, microscopic analysis of prokaryotic cells and virus particles showed their presence after the application of both membrane types; TCN 3.0 × 10² cells/mL–UF 200 kDa, 5.0 × 10³ cells/mL–UF 400 kDa, VP 1.0 × 10⁵/mL. The presence of potentially pathogenic, highly infectious virus particles means that ultrafiltration cannot be considered a sufficient disinfection method for treated wastewater diverted for reuse or discharged from high load wastewater treatment plants to recreational areas. For full microbiological safety it would be advisable to apply an additional disinfection method (e.g., ozonation).

Concerns and strategies for wastewater treatment during COVID-19 pandemic to stop plausible transmission

Along with outbreak of the pandemic COVID-19 caused by SARS-CoV-2, the problem of biomedical wastewater disposal has caused widespread public concern, as reportedly the presence is confirmed in wastewater. Keeping in mind (i) available evidence indicating need to better understand potential of wastewater mediated transmission and (ii) knowledge gaps in its occurrence, viability, persistence, and inactivation in wastewater, in this present work, we wanted to re-emphasize some strategies for management of SARS-CoV-2 contaminated wastewater to minimise any possible secondary transmission to human and environment. The immediate challenges to consider while considering wastewater management are uncertainty about this new biothreat, relying on prediction based treatments options, significant population being the latent asymptomatic carrier increased risk of passing out of the virus to sewage network, inadequacy of wastewater treatment facility particularly in populated developing countries and increased generation of wastewater due to increased cleanliness concern. In absence of regulated central treatment facility, installation of decentralized wastewater treatment units with single or multiple disinfection barriers in medical units, quarantine centre, isolation wards, testing facilities seems to be urgent for minimizing any potential risk of wastewater transmission. Employing some emerging disinfectants (peracetic acid, performic acid, sodium dichloro isocyanurate, chloramines, chlorine dioxide, benzalconium chloride) shows prospects in terms of virucidal properties. However, there is need of additional research on coronaviruses specific disinfection data generation, regular monitoring of performance considering all factors influencing virus survival, performance evaluation in actual water treatment, need of augmenting disinfection dosages, environmental considerations to select the most appropriate disinfection technology.

Inactivation of Bacteria by Peracetic Acid Combined with Ultraviolet Irradiation: Mechanism and Optimization

Peracetic acid (PAA) is an emerging disinfectant for municipal wastewater treatment owing to good biocidal effects and limited harmful by-product formation. This study investigated the inactivation of Gram-negative Escherichia coli (E. coli) and Gram-positive Enterococcus durans (E. durans) and Staphylococcus epidermidis (S. epidermidis) by PAA combined with UV concurrently (UV/PAA) or sequentially (PAA-UV/PAA) for enhanced disinfection. Under UV/PAA, the contributions of different mechanisms (UV, PAA, reactive radicals (mainly ^•OH and CH₃C(O)OO^•), and the synergistic effect of all mechanisms involved) to the overall inactivation were quantitatively assessed. Results revealed that radicals played a moderate role in the enhanced disinfection, while the synergistic effect presented a greater contribution, which could be partially linked to the diffusion of PAA into the cells as evidenced for the first time by a fluorescence microscopic method. Taking advantage of PAA diffusion into bacteria, pre-exposure of PAA followed by UV/PAA was demonstrated to yield the highest disinfection efficiency. Indeed, compared to UV/PAA, PAA-UV/PAA could achieve additional 4.7-5.4, 4.1-5.3, and 2.9-3.4 log inactivation of E. coli, E. durans, and S. epidermidis, respectively, in clean water and secondary/tertiary wastewater effluents when the same amounts of PAA and UV doses were applied in both approaches. Bacterial regrowth tests confirmed minimal regrowth potential after the disinfection.

Degradation of pharmaceutical mixtures in aqueous solutions using UV/peracetic acid process: Kinetics, degradation pathways and comparison with UV/H2O2

This paper presents an evaluation of UV/PAA process for degradation of four pharmaceuticals venlafaxine (VEN), sulfamethoxazole (SFX), fluoxetine (FLU) and carbamazepine (CBZ) with comparison to UV/H₂O₂ process. The effectiveness of combining PAA and H₂O₂ at various proportions while irradiating with UVC were also evaluated. UVC/PAA (λ = 254 nm) was effective in degrading all four pharmaceuticals and followed pseudo first-order kinetics. Increasing PAA dosage or UVC intensity resulted in a linear increase in pseudo-first order rate coefficient. Both PAA in dark conditions and UVA/PAA (λ = 360 nm) were marginally effective to degrade SFX and ineffective to degrade VEN, CBZ and FLU; indicating the need for UVC irradiation for activation of PAA. For similar oxidant dosages of 50 mg/L UVC/H₂O₂ was found to be faster than UV/PAA for VEN, CBZ and FLU by 55%, 75% and 33%, respectively. Under similar conditions, SFX was degraded 24% faster by UV/PAA. Increase in the proportion of H₂O₂ to PAA in UVC/PAA/H₂O₂ improved kinetics of degradation compared to PAA alone. Tests on TOC were conducted to determine the amount of acetic acid that is released to water when treatment by UVC/PAA is conducted. Results demonstrated that 70% of PAA by mass was ultimately converted to acetic acid and remained in the treated solutions. Hydroxyl radical attack is hypothesized to be the main mechanism of degradation by UV/PAA as degradation intermediates identified for all the target pharmaceuticals coincided with by-products identified during UV/H₂O₂ process.

Magnetic porous NiLa-Layered double oxides (LDOs) with improved phosphate adsorption and antibacterial activity for treatment of secondary effluent

The removal of phosphate (nutrient) and E. coli (pathogen) from secondary effluent is of great importance to control the water quality of the receiving water bodies. In this study, magnetic porous NiLa-layered double oxides (NiLa-LDOs/Fe₃O₄) were synthesized using a simple co-precipitation method. NiLa-LDOs/Fe₃O₄ exhibited a high phosphate adsorption capacity of 203.10 mg g^-1 in batch adsorption experiments, which can mostly be maintained within the pH range (5.5-8.5) and ionic strength range (5-20 mM) of secondary effluent, and in the presence of commonly co-existing species (anions and organics). NiLa-LDOs/Fe₃O₄ were further evaluated in real secondary effluent and the homogenous surface diffusion model (HSDM) was used to predict the performance in field applications. Under typical conditions, NiLa-LDOs/Fe₃O₄ can last for ∼1845-2448 bed volumes (BVs) before the phosphate concentration in the effluent exceeds the monthly average limit of 1 mg L^-1 P. Good regeneration capacities were also demonstrated in cyclic adsorption-desorption runs in both synthetic solution and secondary effluent. In addition, the presence of Ni and La species greatly enhanced the antibacterial performance of the NiLa-LDOs/Fe₃O₄ toward E. coli. Results obtained from this study indicate porous NiLa-LDOs/Fe₃O₄ can be a promising multifunctional material for the treatment of secondary effluent.

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.

Effects of total suspended solids, particle size, and effluent temperature on the kinetics of peracetic acid decomposition in municipal wastewater

In this study, the influence of total suspended solids (TSS) and particle size as well as effluent temperature on peracetic acid (PAA) decomposition kinetics in municipal wastewater was investigated. PAA decomposition was best described following second order kinetics in primary effluent (PE) and first order kinetics in secondary effluent (SE) samples. For synthetic samples prepared by varying TSS levels, PAA demand increased on average by about 0.042 mg/L in PE and 0.034 mg/L in SE for every 10 mg/L increase in TSS. Similarly, the PAA decay rate constant in these samples increased at a rate of 0.0014 L/mg.min and 0.00039 min^-1, respectively, per 10 mg/L TSS. To examine the effect of particle size, synthetic samples with narrow size fractions (20-45, 45-75, and 75-90 μm) were prepared. It was found that samples with smaller particle size fractions had a greater PAA demand and decay rate constant. Effluent temperature also enhanced the PAA decomposition rate with the calculated activation energies for PE and SE samples being 29,980 J/mol and 34,860 J/mol, respectively.

Novel Methods for Efficacy Testing of Disinfectants – Part I

The pathogens which are the effective transmitters of various infections pose a serious problem in restraining their interference in maintaining a sterile environment. The practical applicability of traditional methods of disinfection is restricted due to their cumbersomeness, toxic product generation, and cost-effectiveness. Therefore, the objective of the current review is to elaborate the efficacies and limitations of various novel disinfectants that can show their activity in a few minutes of treatment. The expected outcome would be feasibility for selection of a favorable disinfectant through various technologies that can generate uniform results and form a basis for the true estimation required parameters. Hence, the current paper ends with the consideration of unique new techniques that distinguishes their simplicity, safety, and efficacy in generating a sterile environment.

Effect of suspended solids on peracetic acid decay and bacterial inactivation kinetics: Experimental assessment and definition of predictive models

The work addresses the effect of total suspended solids (TSS) on disinfection by peracetic acid (PAA) concerning both PAA decay and bacterial inactivation kinetics. The effect of TSS on PAA decay was evaluated at five TSS concentrations (5, 40, 80, 120 and 160 mg/L), obtained from stock TSS solutions prepared from activated sludge samples. The influence of the soluble matter associated to the suspended solids on PAA decay was evaluated separately, using the same stock TSS solution after the removal of solids by filtration. The contributions of suspended and soluble fractions were found to be independent, and a predictive model formed by two additive sub-models was proposed to describe the overall PAA decay kinetics. Moreover, an uncertainty analysis was performed by a series of Monte Carlo simulations to propagate the uncertainties associated to the coefficients of the model. Then, the disinfectant dose (mg/L min) was highlighted as the main parameter determining disinfection efficiency on a pure culture of E. coli and an inactivation kinetic model was developed based on the response of E. coli to various PAA doses. Finally, the effect of TSS (40 and 160 mg/L) on the inactivation of free-swimming E. coli was investigated at two PAA doses (5 and 20 mg/L min). TSS reduced inactivation extent an average of 0.4 logs at 5 mg/L min and 1.5 logs at 20 mg/L min. It was hypothesized that this might be due to the formation of bacteria aggregates as defense mechanism against disinfection, enhanced by the presence of solids.

Thermodynamic properties of an emerging chemical disinfectant, peracetic acid

Peracetic acid (PAA or CH₃COOOH) is an emerging disinfectant with a low potential to form carcinogenic disinfection by-products (DBPs). Basic thermodynamic properties of PAA are, however, absent or inconsistently reported in the literature. This review aimed to summarize important thermodynamic properties of PAA, including standard Gibbs energy of formation and oxidation-reduction (redox) potential. The standard Gibbs energies of formation of CH₃COOOH_(aq), CH₃COOOH_(g), CH₃COOOH_(l), and CH₃COOO_(aq)^- are -299.41kJ·mol^-1, -283.02kJ·mol^-1, -276.10kJ·mol^-1, and -252.60kJ·mol^-1, respectively. The standard redox potentials of PAA are 1.748V and 1.005V vs. standard hydrogen electrode (SHE) at pH 0 and pH 14, respectively. Under biochemical standard state conditions (pH 7, 25°C, 101,325Pa), PAA has a redox potential of 1.385V vs. SHE, higher than many disinfectants. Finally, the environmental implications of the thermodynamic properties of PAA were systematically discussed. Those properties can be used to predict the physicochemical and biological behavior of aquatic systems exposed to PAA.

Methodology for modeling the disinfection efficiency of fresh-cut leafy vegetables wash water applied on peracetic acid combined with lactic acid

A methodology to i) assess the feasibility of water disinfection in fresh-cut leafy greens wash water and ii) to compare the disinfectant efficiency of water disinfectants was defined and applied for a combination of peracetic acid (PAA) and lactic acid (LA) and comparison with free chlorine was made. Standardized process water, a watery suspension of iceberg lettuce, was used for the experiments. First, the combination of PAA+LA was evaluated for water recycling. In this case disinfectant was added to standardized process water inoculated with Escherichia coli (E. coli) O157 (6logCFU/mL). Regression models were constructed based on the batch inactivation data and validated in industrial process water obtained from fresh-cut leafy green processing plants. The UV254(F) was the best indicator for PAA decay and as such for the E. coli O157 inactivation with PAA+LA. The disinfection efficiency of PAA+LA increased with decreasing pH. Furthermore, PAA+LA efficacy was assessed as a process water disinfectant to be used within the washing tank, using a dynamic washing process with continuous influx of E. coli O157 and organic matter in the washing tank. The process water contamination in the dynamic process was adequately estimated by the developed model that assumed that knowledge of the disinfectant residual was sufficient to estimate the microbial contamination, regardless the physicochemical load. Based on the obtained results, PAA+LA seems to be better suited than chlorine for disinfecting process wash water with a high organic load but a higher disinfectant residual is necessary due to the slower E. coli O157 inactivation kinetics when compared to chlorine.

Nondeterministic computational fluid dynamics modeling of Escherichia coli inactivation by peracetic acid in municipal wastewater contact tanks

Wastewater disinfection processes are typically designed according to heuristics derived from batch experiments in which the interaction among wastewater quality, reactor hydraulics, and inactivation kinetics is often neglected. In this paper, a computational fluid dynamics (CFD) study was conducted in a nondeterministic (ND) modeling framework to predict the Escherichia coli inactivation by peracetic acid (PAA) in municipal contact tanks fed by secondary settled wastewater effluent. The extent and variability associated with the observed inactivation kinetics were both satisfactorily predicted by the stochastic inactivation model at a 95% confidence level. Moreover, it was found that (a) the process variability induced by reactor hydraulics is negligible when compared to the one caused by inactivation kinetics, (b) the PAA dose required for meeting regulations is dictated equally by the fixed limit of the microbial concentration as well as its probability of occurrence, and (c) neglecting the probability of occurrence during process sizing could lead to an underestimation of the PAA dose required by as much as 100%. Finally, the ND-CFD model was used to generate sizing information in the form of probabilistic disinfection curves relating E. coli inactivation and probability of occurrence with the average PAA dose and PAA residual concentration at the outlet of the contact tank.

Growth inhibition of Aeromonas salmonicida and Yersinia ruckeri by disinfectants containing peracetic acid

Peracetic acid (PAA) is a therapeutic agent used for disinfection in aquaculture, but it must be investigated thoroughly in order to mitigate diseases without harming the fish. Successful disinfectants (like PAA) should not leave dangerous residues in the environment in order to successfully contribute to sustainable aquaculture. The aim of our study was to compare the effectiveness of 6 commercial PAA products with different molecular PAA:H2O2 ratios to reduce bacterial growth of Aeromonas salmonicida and Yersinia ruckeri and to determine effective concentrations and exposure times. All products reduced colony-forming units (CFUs) of A. salmonicida and Y. ruckeri. Products with higher molecular PAA:H2O2 ratios inhibited growth better than products with lower molecular PAA:H2O2 ratios at the same PAA concentration; this indicates that H2O2 is not the driving force in the reduction of A. salmonicida and Y. ruckeri growth by PAA in vitro. The practical application of the products with high molecular PAA:H2O2 ratios should be prioritized if these pathogens are diagnosed.

Onboard ship evaluation of the effectiveness and the potential environmental effects of PERACLEAN Ocean for ballast water treatment in very cold conditions

This study verified the effectiveness and the potential toxic impact of PERACLEAN Ocean ballast water treatment for very cold freshwater (0.1-0.5 degrees C) in real ballast tank (750 m(3)) conditions aboard a ship and in large-volume (4.5 m(3)) polyethylene tanks. Concentrations of peracetic acid (PAA) and hydrogen peroxide (H2O2) gradually dropped by 41-59% over 5 days. The treatment altered the quality of the treated waters by causing a pH drop of 0.9-1.3 units and a fourfold to sevenfold increase in dissolved organic carbon and organophosphates concentrations. More than 90% of the biomass of free-floating micro-organisms and viable phytoplankton were eliminated within 48 h after treatment. The treatment resulted in 100% mortality in caged fish exposed to treated waters but was totally ineffective against adult zebra mussels and some nematods living in tank sediments. Toxic response from ecotoxicological assays indicated that treated waters after 5 days should be diluted by a factor of 1:2 to 1:200 to reduce toxicity below selected endpoints of acute lethality tests. On the basis of PAA degradation rate, fresh waters treated with 100-ppm PERACLEAN Ocean should be kept in ballast tanks for 15-20 days after treatment to reduce toxicity. It is concluded that the treatment can be an effective biocide to rapidly eliminate organisms of the water column inside the ballast tanks over a wide range of environmental conditions, but that the discharge of the toxic treated waters should be properly managed to minimize potential environmental impact.

Adding silver and copper to hydrogen peroxide and peracetic acid in the disinfection of an advanced primary treatment effluent

This paper evaluates the efficacy of hydrogen peroxide (HP) and peracetic acid (PAA) in the disinfection of an Advanced Primary Treatment (APT) effluent, and how said disinfection capacities can be enhanced by combining the oxidants with copper (Cu2+) and silver (Ag). The treatment sequence consisted of APT (adding chemicals to water to remove suspended solids by coagulation and flocculation), followed by disinfection with various doses of HP, HP+Cu2+, HP+Ag, PAA and PAA+Ag. Microbiological quality was determined by monitoring concentrations of fecal coliforms (FC), pathogenic bacteria (PB) and helminth eggs (HE) throughout the sequence. The results revealed that APT effluent still contains very high levels of bacteria as the treatment only removes 1-2 log of FC and PB, but the reduction in the number of viable helminth eggs was 83%. Subsequent disinfection stages demonstrated that both HP+Cu2+ and HP+Ag have a marked disinfection capacity for bacteria (3.9 and 3.4 log-inactivation, respectively). Peracetic acid on its own was already extremely efficient at disinfecting for bacteria, and the effect was enhanced when combining PAA with silver (PAA+Ag). The best result for HE removal was achieved by combining PAA with silver (PAA+Ag) at doses of 20 + 2.0 mg l(-1), respectively. The study concluded that the PAA+Ag and HP+Ag combinations were good alternatives for APT effluent disinfection, because the disinfected effluents met the standards in NOM-001-SEMARNAT-1996, Mexico's regulation governing the microbiological quality required in treated wastewater destined for unrestricted reuse in agricultural irrigation (< or =1 helminths per litre). Combining either of these disinfection treatments with a primary method such as APT, therefore, offers an effective and practical way of reducing the health risks normally associated with the reuse of wastewaters.

Peracetic acid disinfection: a feasible alternative to wastewater chlorination

The paper summarizes the results of a bench-scale study to evaluate the feasibility of using peracetic acid (PAA) as a substitute for sodium hypochlorite both for discharge into surface water and for agricultural reuse. Trials were carried out with increasing doses (1, 2, 3, 5, 10, and 15 mg/L) and contact times (6, 12, 18, 36, 42, and 54 minutes) to study disinfectant decay and bacterial removal and regrowth, using fecal coliform and Escherichia coli (E. coli) as process efficiency indicators. Peracetic acid decay kinetics was evaluated in tap water and wastewater; in both cases, PAA decays according to first-order kinetics with respect to time, and a correlation was found between PAA oxidative initial consumption and wastewater characteristics. The PAA disinfection efficiency was correlated with operating parameters (active concentration and contact time), testing different kinetic models. Two data groups displaying a different behavior on the basis of initial active concentration ranges (1 to 2 mg/L and 5 to 15 mg/L, respectively) can be outlined. Both groups had a "tailing-off" inactivation curve with respect to time, but the second one showed a greater inactivation rate. Moreover, the effect of contact time was greater at the lower doses. Hom's model, used separately for the two data groups, was found to best fit experimental data, and the disinfectant active concentration appears to be the main factor affecting log-survival ratios. Moreover, the S-model better explains the initial resistance of E. coli, especially at low active concentrations (< 2 mg/L) and short contact times (< 12 minutes). Microbial counts, performed by both traditional methods and flow cytometry, immediately and 5 hours after sample collection (both with or without residual PAA inactivation), showed that no appreciable regrowth took place after 5 hours, neither for coliform group bacteria, nor for total heterotrophic bacteria.

Virulence of viable but nonculturable S. Typhimurium LT2 after peracetic acid treatment

S. Typhimurium LT2 cells suspended in sterilized sewage effluent water (SEW) and in distilled water microcosms were exposed to 0, 7, 15 and 20 mg/l peracetic acid, and tested for viability and virulence. After treatment for one hour, colony forming units decreased by at least 5 log units at peracetic acid concentration of 7 mg/l. In SEW, at peracetic acid concentration of 15 mg/l, the cells were nonculturable (VNC), but retained virulence as demonstrated by invasion assays of HeLa cells. Higher concentrations (greater than or equal to 20 mg/l) resulted in bacterial death, i.e. substrate non-responsive cells. Despite morphological alterations of the bacteria after peracetic acid treatment, visualized by transmission electronic microscopy, conservation of both adhesive and invasive capacities was confirmed by scanning electron microscopy after exposure to 0-15 mg/l peracetic acid. Public health professionals need to recognize that peracetic acid-treated Salmonella is capable of modifying its physiological characteristics, including entering and recovering from the viable but nonculturable state, and may remain virulent after a stay in SEW followed by peracetic acid treatment.

Peracetic acid (PAA) disinfection of primary, secondary and tertiary treated municipal wastewaters

The efficiency of peracetic acid (PAA) disinfection against enteric bacteria and viruses in municipal wastewaters was studied in pilot-scale. Disinfection pilot-plant was fed with the primary or secondary effluent of Kuopio municipal wastewater treatment plant or tertiary effluent from the pilot-scale dissolved air flotation (DAF) unit. Disinfectant doses ranged from 2 to 7 mg/l PAA in the secondary and tertiary effluents, and from 5 to 15 mg/l PAA in the primary effluents. Disinfection contact times were 4-27 min. Disinfection of secondary and tertiary effluents with 2-7 mg/l PAA and 27 min contact time achieved around 3 log reductions of total coliforms (TC) and enterococci (EC). PAA disinfection also significantly improved the hygienic quality of the primary effluents: 10-15 mg/l PAA achieved 3-4 log reductions of TC and EC, 5 mg/l PAA resulting in below 2 log reductions. F-RNA coliphages were more resistant against the PAA disinfection and around 1 log reductions of these enteric viruses were typically achieved in the disinfection treatments of the primary, secondary and tertiary effluents. Most of the microbial reductions occurred during the first 4-18 min of contact time, depending on the PAA dose and microorganism. The PAA disinfection efficiency remained relatively constant in the secondary and tertiary effluents, despite of small changes of wastewater quality (COD, SS, turbidity, 253.7 nm transmittance) or temperature. The disinfection efficiency clearly decreased in the primary effluents with substantially higher microbial, organic matter and suspended solids concentrations. The results demonstrated that PAA could be a good alternative disinfection method for elimination of enteric microbes from different wastewaters.

Inactivation of enteric microorganisms with chemical disinfectants, UV irradiation and combined chemical/UV treatments

The relative disinfection efficiencies of peracetic acid (PAA), hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl) against Escherichia coli, Enterococcus faecalis, Salmonella enteritidis and coliphage MS2 virus were studied in laboratory-scale experiments. This study also evaluated the efficiency of combined PAA/ultraviolet irradiation (UV) and H2O2/UV treatments to determine if the microbial inactivation was synergistic. Microbial cultures were added into a synthetic wastewater-like test medium and treated by chemical disinfectants with a 10 min contact time, UV irradiation or the combination of chemical and UV treatments. A peracetic acid dose of 3 mg/l resulted in approximately 2-3 log enteric bacterial reductions, whereas 7-15 mg/l PAA was needed to achieve 1-1.5 log coliphage MS2 reductions. Doses of 3-150 mg/l hydrogen peroxide achieved below 0.2 log microbial reductions. Sodium hypochlorite treatments caused 0.3-1 log microbial reductions at an 18 mg/l chlorine dose, while 2.6 log reductions of E. faecalis were achieved at a 12 mg/l chlorine dose. The results indicate that PAA could represent a good alternative to chlorine compounds in disinfection procedures, especially in wastewaters containing easily oxidizable organic matter. Hydrogen peroxide is not an efficient disinfectant against enteric microorganisms in wastewaters. The combined PAA/UV disinfection showed increased disinfection efficiency and synergistic benefits with all the enteric bacteria tested but lower synergies for the coliphage MS2. This suggests that this method could improve the efficiency and reliability of disinfection in wastewater treatment plants. The combined H2O2/UV disinfection only slightly influenced the microbial reductions compared to UV treatments and showed some antagonism and no synergies.

A discussion paper on challenges and limitations to water reuse and hygiene in the food industry

Drinking water is becoming a scarce resource in many areas and both use of water and wastewater outlet are of major ecological and economical importance in many countries. Consumption and discharge may be considerably minimized by means of water reuse. The food industry has a large consumption of water, but until now very limited reuse has taken place due to legislations constraints and hygienic concerns. Legal space for use of water of qualities other than drinking water has been opened with the current legislation. This will, however, in many cases require careful analyses of individual cases based on a thorough understanding of the hazards involved in order to avoid compromising the safety of the food product and thereby the health of consumers. Implementation of water reuse practices in the food industry presents a great challenge for both companies and public health authorities regarding knowledge, technical expertise and documentation. Regulatory, technological, monitoring, verification and ethical aspects associated with microbiologically safe reuse of water in the food industry are discussed and some examples of the challenges ahead and possible approaches are given.

Disinfection of wastewater with peracetic acid: a review

Peracetic acid is a strong disinfectant with a wide spectrum of antimicrobial activity. Due to its bactericidal, virucidal, fungicidal, and sporicidal effectiveness as demonstrated in various industries, the use of peracetic acid as a disinfectant for wastewater effluents has been drawing more attention in recent years. The desirable attributes of peracetic acid for wastewater disinfection are the ease of implementing treatment (without the need for expensive capital investment), broad spectrum of activity even in the presence of heterogeneous organic matter, absence of persistent toxic or mutagenic residuals or by-products, no quenching requirement (i.e., no dechlorination), small dependence on pH, short contact time, and effectiveness for primary and secondary effluents. Major disadvantages associated with peracetic acid disinfection are the increases of organic content in the effluent due to acetic acid (AA) and thus in the potential microbial regrowth (acetic acid is already present in the mixture and is also formed after peracetic acid decomposition). Another drawback to the use of peracetic acid is its high cost, which is partly due to limited production capacity worldwide. However, if the demand for peracetic acid increases, especially from the wastewater industry, the future mass production capacity might also be increased, thus lowering the cost. In such a case, in addition to having environmental advantages, peracetic acid may also become cost-competitive with chlorine.

Peracetic acid as an alternative wastewater disinfectant to chlorine dioxide

AIMS

The aim of this study was to compare the efficiency of peracetic acid with that of chlorine dioxide in the disinfection of wastewater from a sewage treatment plant (serving about 650 000 inhabitants) that has been using peracetic acid as a disinfectant since 1998.

METHODS AND RESULTS

A total of 23 samplings were made, each consisting of three samples: from secondary effluent, effluent disinfected with 2 mg l(-1) of peracetic acid and effluent disinfected with 2.2 mg l(-1) of chlorine dioxide (contact time 20 min). For each sample, measurements were made of the heterotrophic plate count at 36 degrees C, total and faecal coliforms, Escherichia coli, enterococci, pH, suspended solids and chemical oxygen demand (COD). During the first phase of the experiment the peracetic acid was seen to be less efficient than chlorine dioxide. To improve the disinfectant action a system of mechanical agitation was added which led to a greater efficiency in the inactivation of bacteria of faecal origin.

CONCLUSIONS

Both products were found to be influenced by the level of microbial contamination, the amount of suspended solids and COD but not by the pH of the effluent before disinfection. The immediate mixing of the wastewater and disinfectant caused a greater reduction in enterococci.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since peracetic acid was seen to produce a high abatement of micro-organisms, it can be considered as a valid alternative to chlorine dioxide in the disinfection of wastewaters.