Chlorine Tolerance Research Articles

Chlorine Tolerance and Inactivation of Escherichia coli recovered from Wastewater Treatment Plants in the Eastern Cape, South Africa

This study investigated the survival of Escherichia coli (E. coli) recovered from secondary effluents of two wastewater treatment plants in the Eastern Cape Province, South Africa, in the presence of different chlorine concentrations. The bacterial survival, chlorine lethal dose and inactivation kinetics at lethal doses were examined. The bacterial isolates were identified by 16S rRNA gene sequencing. Comparison of the nucleotide sequences of 16S rRNA gene of bacteria with known taxa in the GenBank revealed the bacterial isolates to belong to Escherichia coli. At the recommended free chlorine of 0.5 mg/L, reduction of E. coli isolates (n = 20) initial bacterial concentration of 8.35–8.75 log was within a range of 3.88–6.0 log at chlorine residuals of 0.14–0.44 mg/L after 30 min. At higher doses, a marked reduction (p < 0.05) in the viability of E. coli isolates was achieved with a greater than 7.3 log inactivation of the bacterial population. Inactivation kinetics revealed a high rate of bacterial kill over time (R2 > 0.9) at chlorine dose of 1.5 mg/L. This study indicates poor removal of bacteria at free chlorine at 0.5 mg/L and a greater efficacy of 1.5 mg/L in checking E. coli tolerance.

Improving the chlorine-tolerant ability of polypiperazine-amide nanofiltration membrane by adding NH2-PEG-NH2 in the aqueous phase

A novel polypiperazine-amide nanofiltration (NF) membrane with very high salt rejection was successfully developed in this work. The NF membrane chlorine-tolerant ability were improved greatly after mixing a small amount of α,ω-diamino poly(ethylene glycol) (NH2-PEG-NH2) with piperazine (PIP) in the aqueous phase. The XPS result demonstrated that the polymerization degree of the NF membrane was notably enhanced with the addition of NH2-PEG-NH2. The solute rejections and chlorine tolerance were improved remarkably, while the permeate flux remained almost at the same level. When the NH2-PEG-NH2 (2kDa) content in the total amine was 1%w/w (0.01%w/v in the aqueous solution), NF membrane performance was optimal. This membrane exhibited a pure water flux (PWF) of 34.9Lm−2h−1 along with Na2SO4, MgSO4, MgCl2 and NaCl rejections of 99.5%, 99.2%, 90.9% and 58.3% (2000ppm, 6bar, 25°C), respectively. Moreover, the NF membrane performance was maintained after being treated by 14,000ppm NaClO for 1h. Therefore, adding a small amount of NH2-PEG-NH2 in the aqueous phase could be considered to be an effective way to improve the polypiperazine-amide NF membrane chlorine-tolerant ability.

Assessment of chlorine tolerance profile of Citrobacter species recovered from wastewater treatment plants in Eastern Cape, South Africa.

This present study assessed the chlorine tolerance of some Citrobacter species recovered from secondary effluents from the clarifiers of two wastewater treatment plants in the Eastern Cape, South Africa. The bacterial survival, chlorine lethal dose and inactivation kinetics at lethal doses were examined. Inactivation of the test bacteria (n=20) at the recommended dose of 0.5mg/l for 30min exposure showed a progressive reduction in bacterial population from 4 to 5 log reduction and residuals ranged between 0.12 and 0.46mg/l. The bactericidal activity of chlorine increased at higher dosages with a substantial reduction in viability of the bacteria and complete inactivation of the bacterial population at a lethal dose of 0.75 and 1.0mg/l in 30min. For the inactivation kinetics, bactericidal activity of chlorine increased with time showing a 3.67-5.4 log reduction in 10min, 4.0-5.6 log reduction in 20min and above 6.3 log reductions to complete sterilization of bacterial population over 30min for all the entire test Citrobacter isolates used in this study. Furthermore, there was a strong correlation (R 2>0.84) between bacteria inactivation and increase in contact time. This study appears to have provided support for laboratory evidence of bacterial tolerance to chlorine disinfection at current recommended dose (0.5mg/l for 30min), and chlorine concentration between 0.75 and 1.0mg/l was found to have a better disinfecting capacity to check tolerance of Citrobacter species.

Evidence of emerging challenge of chlorine tolerance of Enterococcus species recovered from wastewater treatment plants

This study assessed the survival of some Enterococcus species recovered from the clarifier of two selected wastewater treatment plants in the Eastern Cape Province, South Africa, in the presence of different concentrations of chlorine disinfectant. The bacterial survival, lethal dose and inactivation kinetics at lethal doses were examined. Inactivation of the test bacteria (n = 20) at the recommended dose of 0.5 mg l−1 progressively increased from 3.0–5.8 log reduction within the range of chlorine residual of 0.14–0.45 mg l−1 after 30 min. The bactericidal activity of chlorine increased at higher chlorine dosages with a significant reduction in viability of the bacteria and complete sterilization of the bacterial population was achieved at a lethal dose of 0.75 mg l−1 and 1.0 mg l−1 in 30 min. For the inactivation kinetics, bactericidal activity of chlorine increased with time showing a 3.0–6.8 log reduction in 10 min, 4.0–8.3 log reduction in 20 min and above 7.9 log reduction in 30 min for all test Enterococcus isolates used in this study. Chlorine dose of 0.75 mg l−1–1.0 mg−1 showed a better disinfecting capacity to effectively reduce the tolerance of Enterococcus species.

The chlorination mechanism of integrally asymmetric cellulose triacetate (CTA)-based and thin film composite polyamide-based forward osmosis membrane

This study investigates the change in performance and properties of various forward osmosis (FO) membranes resulting from exposure to chlorine by conducting performance test and characterization using ATR-FTIR, XPS, zeta potential, NMR and, particularly, ToF-SIMS analyses. The data obtained through the ToF-SIMS measurements suggested that chlorine first reacted with the acetyl/acetate group of the cellulose triacetate (CTA)-based membrane and then with the pyranose ring. Chlorine bound to the membrane surface weakened the H-bond of the CTA-based membrane, resulting in an increase in water flux and reverse salt flux (RSF) as the chlorine exposure time or chlorine concentration increased. A high chlorine dosage cleaved the pyranose ring, leading to loss of membrane selectivity. After chlorination with a high chlorine dosage, the structure of the CTA-based membrane eventually presented fatigue upon an increase in filtration time, and the oxidation of the CTA-based membrane due to exposure to chlorine was maximal at pH 7. The polyamide (PA)-based FO membrane was more sensitive to chlorine under acidic conditions, resulting in a greater loss of selectivity than that of the CTA-based FO membrane. However, an alkaline chlorine solution insignificantly affected both the CTA-based and TFC-based FO membranes. This study shows that the TFC PA-based FO membrane yields a high water flux, but its chlorine tolerance must be improved to be practically applicable in various fields.

Improved chlorine tolerance of a polyvinyl pyrrolidone-polysulfone membrane enabled by carboxylated carbon nanotubes

Chemical cleaning of membranes may be limited by the tolerance of some polymeric membranes to chlorine. In this work we show that modification of a polyvinyl pyrrolidone-polysulfone (PVP-PSF) membrane with carboxylated carbon nanotubes (CNTs) leads to greater chlorine tolerance of the membrane along with smoothing the surface roughness and improving some membrane properties including permeability, hydrophilicity and antifouling ability. In comparison with PVP-PSF membrane, incorporating carboxylated CNTs reduced the release of organic matter from the membrane and caused less decrease in hydrophilicity, permeability and BSA rejection. After chlorine treatment of a conventional PVP-PSF membrane, an infrared absorbance peak around 1670 cm−1, representing the vibration of the amide bond in the PVP, decreased significantly and two smaller peaks at around 1725 and 1775 cm−1 were observed. The percentage of C−Cl (2p) in the PVP-PSF membrane was about 2.8 times greater than that of the carboxylated CNT-composite PVP-PSF (CNT-PVP-PSF) membrane after chlorine exposure, suggesting greater chlorine tolerance of CNT-PVP-PSF membrane. In comparison with PVP-PSF membrane, the formation of toxic chlorinated byproducts during chlorination of organic matter released from CNT-PVP-PSF membrane was much lower. The improvement of tolerance to chlorine is attributed to stabilization of the polymer through hydrogen bonding between polymer and carboxylated CNTs.

High Performance and Chlorine Resistant Carbon Nanotube/Aromatic Polyamide Reverse Osmosis Nanocomposite Membrane

ABSTRACTEfficient water desalination constitutes a major challenge for the next years and reverse osmosis membranes will play a key role to achieve this target. In this work, a high-performance reverse osmosis nanocomposite membrane was prepared by interfacial polymerization in presence of multiwalled carbon nanotubes. The effect of carbon nanotubes on the chlorine resistance, antifouling and desalination performance of the nanocomposite membranes was studied. We found that the addition of carbon nanotubes not only improved the membrane performance in terms of flow and antifouling, but also inhibited the chlorine degradation of these membranes. Several reports have acknowledged the benefits of adding carbon nanotubes to aromatic PA nanocomposite membranes, but little attention has been paid to the mechanisms related to the improvement of flow rate, selectivity and chlorine tolerance. We carried out a comprehensive study of the chemical and physical effects of carbon nanotubes on the fully crosslinked polyamide network. The chemical structure, chlorine resistance and membrane degradation was studied by several analytical techniques, permeation and fouling studies, whereas the microstructure of the nanocomposite was studied by small and wide angle X-ray scattering, high resolution transmission electron microscopy, and molecular dynamics. We found that the addition of the nanotube affects the interfacial polymerization, resulting in a polymer network with smaller pore size and higher sodium and chlorine rejection. We simulated the hydration of the membrane in seawater and found that the radial distribution function of water confined in the pores of the nanocomposite membrane exhibited smaller clusters of water molecules, thus suggesting a dense membrane structure. We analysed the network mobility and found that the nanotube provides mechanical stability to the polymer matrix. This study presents solid evidence towards more efficient and robust reverse osmosis membranes using carbon nanotubes as mechanical reinforcing and chlorine protection additive.

Sulfonated polysulfone supported high performance thin film composite membranes for forward osmosis

Abstract Sulfonated polymers have shown great promise as a material for membranes in water purification. Their hydrophilic nature combined with impressive chemical stability has yielded unique membranes with desalination capacity combined with chlorine tolerance. In this work, we explore the use of these polymers in support materials for thin film composite (TFC) membranes for forward osmosis (FO). Our reasoning behind their use lies in their intrinsic hydrophilicity, which promotes wetting and mass transfer in this support layer. We combine the use of this supporting material with different polyester (PET) nonwoven backings in order to better understand how backing choice and membrane midlayer material choice interrelate. By varying the degree of sulfonation in the support midlayer, along with selecting backing nonwovens with appropriate characteristics, our best membranes exhibited water flux of about 70 L m−2 h−1 using 1 M sodium chloride draw solution against deionized water in PRO mode. The use of the PET in these membrane imparted impressive mechanical properties while still keeping the structural parameter low (as low as 277 μm). This is the lowest structural parameter of the fabric backed TFC membranes reported in the open literature. These results suggest that the combination of sulfonated polymer midlayers with appropriate PET nonwovens could serve to inform next generation membrane designs for forward and pressure retarded osmosis.

Improved chlorine resistance of polyamide thin-film composite membranes with a terpolymer coating

Abstract Polyamide (PA) thin-film composite (TFC) membranes are easily degraded under the attack of active chlorine in feed water or during chemical washing. In the present work, a random terpolymer of 2-acrylamido-2-methyl propanesulfonic acid, acrylamide and 1-vinylimidazole (P(AMPS-co-Am-co-VI)) was designed as a coating material to improve the chlorine tolerance of PA TFC membrane. The terpolymer was first synthesized via conventional free radical polymerization and then coated onto commercial available PA TFC membrane by dip-coating process. The changes in surface chemistry, morphology, hydrophilicity/hydrophobicity and charge characteristics of the membrane after surface coating were investigated in detail. It was shown that the incorporation of terpolymer coating created a more neutral, hydrophilic, and smooth membrane surface. The chlorine resistance of the membranes was evaluated by comparing the permeation and separation properties of the unmodified and modified membranes after chlorine exposure. And the experimental results indicated that the chlorine tolerance of PA TFC membranes was improved significantly, especially in acid environment. The coating layer prevents the selective layer from the attack of active chlorine as a barrier layer more than a sacrificial layer. The coating material and method developed in this work can facilitate the design and manufacture of highly chlorine resistant TFC membrane for seawater desalination and industrial separation.

Preparation and characterization of a positively charged nanofiltration membrane based on poly(arylene ether sulfone) with tertiary amine groups

A type of poly(arylene ether sulfone) with pendant tertiary amine groups (PSDA) was synthesized via nucleophilic substitution polymerization of 3,3′-dimethylaminemethylene-4,4′-oxybisphenol (DABP) and 4,4′-bisfluorodiphenyl sulfone(BFDPS). The resulting polymer was used to prepare a nanofiltration membrane via a convenient one-step phase inversion process. The preparation conditions were investigated; the optimum parameters were 30 wt% PSDA, 30 wt% THF, 40 wt% DMF casting solution, and 10 s evaporation time. The zeta potential test indicated that the PSDA membranes were positively charged below pH 11.0. The results of the membrane performance testing showed that the trend for rejection was RFeCl3 > RMgCl2 ≈ RCaCl2 > RNaCl > RNa2SO4 (R=rejection), which was a typical positively charged nanofiltration membrane performance. The PSDA membrane also showed excellent chlorine tolerance; no obvious performance change was observed after exposure to an aqueous NaOCl solution (active chlorine concentration no less than 1000 ppm) for 15 days.

Preventing community-wide transmission of Cryptosporidium: a proactive public health response to a swimming pool-associated outbreak--Auglaize County, Ohio, USA.

The incidence of recreational water-associated outbreaks in the United States has significantly increased, driven, at least in part, by outbreaks both caused by Cryptosporidium and associated with treated recreational water venues. Because of the parasite's extreme chlorine tolerance, transmission can occur even in well-maintained treated recreational water venues (e.g. pools) and a focal cryptosporidiosis outbreak can evolve into a community-wide outbreak associated with multiple recreational water venues and settings (e.g. childcare facilities). In August 2004 in Auglaize County, Ohio, multiple cryptosporidiosis cases were identified and anecdotally linked to pool A. Within 5 days of the first case being reported, pool A was hyperchlorinated to achieve 99·9% Cryptosporidium inactivition. A case-control study was launched to epidemiologically ascertain the outbreak source 11 days later. A total of 150 confirmed and probable cases were identified; the temporal distribution of illness onset was peaked, indicating a point-source exposure. Cryptosporidiosis was significantly associated with swimming in pool A (matched odds ratio 121·7, 95% confidence interval 27·4-∞) but not with another venue or setting. The findings of this investigation suggest that proactive implementation of control measures, when increased Cryptosporidium transmission is detected but before an outbreak source is epidemiologically ascertained, might prevent a focal cryptosporidiosis outbreak from evolving into a community-wide outbreak.

Does chlorination of seawater reverse osmosis membranes control biofouling?

Biofouling is the major problem of reverse osmosis (RO) membranes used for desalting seawater (SW). The use of chlorine is a conventional and common practice to control/prevent biofouling. Unlike polyamide RO membranes, cellulose triacetate (CTA) RO membranes display a high chlorine tolerance. Due to this characteristic, CTA membranes are used in most of the RO plants located in the Middle East region where the elevated seawater temperature and water quality promote the risk of membrane biofouling. However, there is no detailed study on the investigation/characterization of CTA-RO membrane fouling. In this investigation, the fouling profile of a full–scale SWRO desalination plant operating with not only continuous chlorination of raw seawater but also intermittent chlorination of CTA-RO membranes was studied. Detailed water quality and membrane fouling analyses were conducted. Profiles of microbiological, inorganic, and organic constituents of analysed fouling layers were extensively discussed. Our results clearly identified biofilm development on these membranes. The incapability of chlorination on preventing biofilm formation on SWRO membranes could be assigned to its failure in effectively reaching throughout the different regions of the permeators. This failure could have occurred due to three main factors: plugging of membrane fibers, chlorine consumption by organics accumulated on the front side fibers, or chlorine adaptation of certain bacterial populations.

Efficacy of synthesis conditions on functionalized carbon nanotube blended cellulose acetate membrane for desalination

Cellulose acetate membrane has been applied to reverse osmosis for desalination due to chlorine tolerance and biofouling resistance. Since it requires optimized synthesis condition for application, we investigated the effect of different conditions on membrane performances. It was found that polymer concentration, solvent ratio, and evaporation time were critical to determine membrane selectivity and permeability. Based on the study, optimized conditions were obtained, which were 14 wt% of polymer concentration, 1:2.9 of ratio of 1,4-dioxane to acetone, and 30 s of evaporation time. Further, functionalized multi-walled carbon nanotubes (MWCNTs) were applied to the optimized bare membrane in order to enhance the performances. The composite membranes were characterized by fourier transform infrared spectroscopy, scanning electron microscopy, and contact angle measurement. It was found that the MWCNTs influenced the morphology and surface chemistry of the membrane. This study could contribute to develop a commercial composite RO membrane with nanomaterial for desalination application.

Chlorine resistant binary complexed NaAlg/PVA composite membrane for nanofiltration

A composite nanofiltration (NF) membrane was prepared by coating a thin layer of sodium alginate (NaAlg)-polyvinyl alcohol (PVA) blend on the polysulfone support, then cross linked in two steps with calcium chloride and glutaraldehyde respectively. Structural and morphological characteristics of the NF composite membranes were determined by FT-IR and SEM. The performance of the membrane was evaluated in nanofiltration studies, and the effect on performance of experimental parameters including the NaAlg/PVA blend ratio, cross linking reaction time, membrane thickness and operating time was investigated. The permeance properties of the membrane were determined using 2000ppm solutions of NaCl and MgSO4. A water flux of 80L/m2.h with 46% salt rejection was observed for the monovalent salt solution. However, a decrease in flux to 68L/m2h with an increase in salt rejection to 80% was noticed for the divalent ions. The chlorine tolerance of the composite membrane was tested by exposing it to the NaOCl solution for a different time span. A slight change in water flux and salt rejection was observed, revealing a good stability of the membrane in the chlorine retaining environment. Hence, the prepared binary cross-linked NaAlg/PVA composite membrane can successfully be utilized for the purpose of nanofiltration and/or desalination.

Multi-species biofilms defined from drinking water microorganisms provide increased protection against chlorine disinfection

A model biofilm, formed of multiple species from environmental drinking water, including opportunistic pathogens, was created to explore the tolerance of multi-species biofilms to chlorine levels typical of water-distribution systems. All species, when grown planktonically, were killed by concentrations of chlorine within the World Health Organization guidelines (0.2–5.0 mg l−1). Higher concentrations (1.6–40-fold) of chlorine were required to eradicate biofilm populations of these strains, ∼70% of biofilms tested were not eradicated by 5.0 mg l−1 chlorine. Pathogenic bacteria within the model multi-species biofilms had an even more substantial increase in chlorine tolerance; on average ∼700–1100 mg l−1 chlorine was required to eliminate pathogens from the biofilm, 50–300-fold higher than for biofilms comprising single species. Confocal laser scanning microscopy of biofilms showed distinct 3D structures and multiple cell morphologies and arrangements. Overall, this study showed a substantial increase in the chlorine tolerance of individual species with co-colonization in a multi-species biofilm that was far beyond that expected as a result of biofilm growth on its own.

Evaluation of quaternary phosphonium-based polymer membranes for desalination application

Tris(2,4,6-trimethoxyphenyl)polysulfone-methylene quaternary phosphonium-hydroxide (TPQPOH) membranes were prepared and tested for potential use as desalination membranes. The effects of the curing temperature, a plasticizer and membrane preparation conditions on desalination performance of TPQPOH membranes were studied. After being cured at 80°C for 12h, the TPQPOH membrane exhibited a salt rejection of 53.9% and a water permeability of 9.78Lμmm−2h−1bar−1. When the curing temperature was increased to 120°C, the salt rejection increased whereas there was a drop in water permeability. The addition of polyvinyl butyral (PVB) as the plasticizer was shown to effectively prevent the TPQPOH membranes from cracking, and the resulting membranes possessed increased salt rejection rate and reduced water permeation. Chlorine tolerance tests showed that the membrane prepared from dried TPQPOH was more chlorine resistant than that from wet-TPQPOH. The membrane prepared by dissolving dried TPQPOH in ethanol possessed a high salt rejection of 94.9% and a water permeability of 5.05Lμmm−2h−1bar−1.

Polyamide interfacial composite membranes prepared from m-phenylene diamine, trimesoyl chloride and a new disulfonated diamine

► Polyamide TFCs were prepared from m -phenylenediamine and trimesoyl chloride. ► TFC membranes have 0.4 ± 0.1% NaCl passage and permeate flux of 42 ± 3 L/(m 2 h). ► Post-polymerization thermal treatment did not improve rejection or permeate flux. ► TFC membranes were synthesized from S-BAPS, a disulfonated sulfone diamine and TMC. ► S-BAPS based membranes have higher permeate flux and lower rejection than MPD based ones. The influence of synthesis conditions (e.g., monomer concentration and membrane preparation protocol) on transport properties of polyamide thin-film composite (TFC) membranes prepared using m -phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization is reported. For example, at 25 °C, NaCl rejection and permeate flux combinations of 99.6 ± 0.1% and 42 ± 3 L/(m 2 h), respectively, were achieved in crossflow filtration using a 2000 ppm aqueous solution of NaCl and a transmembrane pressure difference of 225 psi (15.5 bar). Additionally, a sulfone diamine, disulfonated bis[4-(3-aminophenoxy)phenyl]sulfone (S-BAPS), was used in place of MPD to prepare TFC membranes. The resulting membranes had low NaCl rejection but somewhat higher permeate flux than MPD/TMC membranes. These membranes had reduced chlorine tolerance compared to those prepared using MPD as the diamine.

A novel method of surface modification to polysulfone ultrafiltration membrane by preadsorption of citric acid or sodium bisulfite

In membrane processes, various agents are used to enhance, protect, and recover membrane performance. Applying these agents in membrane modification could potentially be considered as a simple method to improve membrane performance without additional process. Citric acid (CI) and sodium bisulfite (SB) are two chemicals that are widely used in membrane feed water pretreatment and cleaning processes. In this work, preadsorptions of CI and SB were developed as simple methods for polysulfone ultrafiltration membrane modification. It was found that hydrogen bonding and Van Der Waals attraction could be responsible for the adsorptions of CI and SB onto membranes, respectively. After modification with CI or SB, the membrane surfaces became more hydrophilic. Membrane permeability improved when modified by SB while decreased a little when modified by CI. The modified membranes had an increase in PEG and BSA rejections and better antifouling properties with higher flux recovery ratios during filtration of a complex pharmaceutical wastewater. Moreover, membrane chlorine tolerance was elevated after modification with either agent, as shown by the mechanical property measurements.

Anti-biofouling organic-inorganic hybrid membrane for water treatment

Biofouling is a critical problem in membrane filtration processes. Herein, we report an anti-biofouling organic-inorganic hybrid membrane for water treatment. Antimicrobial drug (substituted 1,3,4-oxadiazole) with functionalized silica were successfully incorporated into organic phase by sol–gel in aqueous media followed by formal cross-linking to achieve highly stable and anti-biofouling membrane. Structural features of these phosphonic acid functionalized hybrid membranes depended on silica content. Physicochemical properties of prepared membranes revealed their stable (thermal, mechanical, and chemical), chlorine tolerance and charged nature. The most suitable membrane (MO-6) exhibited better performance in comparison to reported membranes. Absence of any deterioration in membrane permeability after 30 days operation under E. coli broth solution, confirmed their anti-biofouling nature.

Elimination of Escherichia coli from oysters using electrolyzed seawater

Electrolyzed seawater (ESW) is reportedly an effective disinfectant for aquaculture equipment because of its simple mechanism and cost effectiveness. The potential of electrolyzed seawater for oyster depuration was studied using different experiments. The first was determination of chlorine tolerance of oysters. Second was effectiveness of ESW against Escherichia coli in artificially contaminated oysters and third was effectiveness of ESW against E. coli in naturally contaminated oysters from two culture farms. Tolerance of oysters for Chlorine was studied by scanning electron microscopy (SEM) and histological observation demonstrating that more than 0.5 mg/L of chlorine was toxic while 0.2 mg/L was safe for the oysters. Oysters artificially contaminated with E. coli (230 MPN/100 mL, 16.5 °C for 15 h) were depurated for 6, 24, and 48 h using ESW and UV irradiated seawater. E. coli counts in artificially contaminated oysters decreased to below the detection limit (30 E. coli MPN/100 g) after depuration with ESW for 24 h or UV irradiated seawater for 6 h. In experiments on naturally contaminated oysters E. coli counts decreased to below detection limits after depuration with ESW for 24 h. From these results, electrolysis of seawater is a useful method for post harvest elimination of E. coli from oysters.