Free Available Chlorine Concentration Research Articles

Inactivation of Avian Influenza Virus Aerosol Using Membrane-Less Electrolyzed Water Spraying

Avian influenza virus (AIV) can have a serious impact on both human and animal health. In this study, we used an environmentally controlled chamber and a hemagglutination assay (HA) to evaluate the ability of membrane-less electrolyzed water (MLEW) spraying to inactivate H6N1 AIV aerosol. MLEW was generated by electrolyzing sodium chloride solution, and then sprayed into the chamber at free available chlorine (FAC) concentrations of 50, 100 and 200 mg/L by means of high-pressure air pumping to inactivate airborne H6N1 AIV aerosols individually. The results showed that MLEW spraying effectively neutralized H6N1 AIV aerosol. In addition, the virucidal ability of MLEW increased as the FAC concentration increased. Five minutes after MLEW spraying at an FAC concentration of 200 mg/L, the H6N1 viral HA titer decreased from 24 to 20. Our work provides important new evidence of the value of spraying with MLEW disinfectant to protect against AIV, which may be further applied for indoor decontamination purposes to promote animal and human health.

Degradation of natural organic matter and disinfection byproducts formation by solar photolysis of free available chlorine

Environment disinfection effectively curbs transmission of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, elevated concentration of free available chlorine (FAC) in disinfectants can be discharged into surface water, generating toxic disinfection byproducts (DBPs). The impact of solar photolysis of FAC on natural organic matter (NOM) to form DBPs has not been well studied. In this work, solar photolysis of FAC was found to result in higher formation of DBPs, DBPs formation potential (DBPsFP), total organic chlorine (TOCl) and lower specific ultraviolet absorbance at 254 nm (SUVA254), compared to dark chlorination. In solar photolysis of FAC, formation of total DBPs was promoted by pH=8, but hindered by the addition of HCO3−, radical scavenger or deoxygenation, while addition of NO3−and NH4+both enhanced the formation of nitrogenous DBPs. Differences in the formation of DBPs in solar photolysis of FAC under various conditions were influenced by reactive species. The formation of trichloromethane (TCM) and haloacetic acids (HAAs) in solar photolysis of FAC positively correlated with the steady-state concentrations of ClO• and O3. The steady-state concentrations of •NO and •NH2 positively correlated with the formation of halonitromethanes (HNMs). HAAs and haloacetonitriles (HANs) mainly contributed to calculated cytotoxicity of DBPs. This study demonstrates that solar photolysis of FAC may significantly impact the formation of DBPs in surface water due to extensive use of disinfectants containing FAC during SARS-CoV-2 pandemic.

Stability of Free Available Chlorine Levels in Dilute Sodium Hypochlorite Solutions over a 6-Week Period.

Animal care and use programs commonly use chlorine and chlorine-based disinfectants to help prevent facility acquired infections in animals. The Department of Comparative Medicine (DCM) at Oregon Health and Science University (OHSU) follows the Centers for Disease Control and Prevention (CDC) disinfection guidelines for preparing and storing these disinfectants. DCM prepares bottles of dilute solutions of sodium hypochlorite (that is, commercial bleach) daily. In this study, we tested whether dilute bleach solutions, as prepared following the DCM protocol, remained stable under real-world practice conditions for up to 6 wk. We tested 4 groups of spray bottles filled with 0.5% bleach solutions in these experiments. Specifically, we sprayed 2 groups of bottles daily to mimic use while 2 other groups of bottles were not sprayed. We then measured free available chlorine (FAC) using 2 methods, spectrophotometry and colorimetric strips. All 4 test groups showed stable maintenance of FAC concentration for the length of the experiment. Mean FAC loss from baseline levels was not significantly different in the group of bottles not sprayed daily (6% for group 2 at week 5 compared with 7% for Group 4 at week 6). All bottles in Groups 1 and 3 measured by colorimetric strips showed concentrations at or near 5000 mg/L at all weekly time points throughout the experiment. This study shows that 0.5% sodium hypochlorite solutions stored and used in a standard rodent housing room and sprayed daily will maintain acceptable FAC concentrations for at least 5 to 6 wk, perhaps longer. In addition, we report that colorimetric strips may be a useful and accessible quality control tool for testing freshly prepared solutions at regular intervals. We conclude that sodium hypochlorite solutions can be prepared on a weekly, biweekly, or monthly basis with no loss in disinfection effectiveness.

Effects of heat in the properties of NaOCl alone and mixed with etidronate and alkaline tetrasodium EDTA.

To assess the free available chlorine concentration (FAC), organic tissue dissolution and smear layer removal capacity of sodium hypochlorite (NaOCl) alone and when mixtured with etidronate (HEDP) and tetrasodium EDTA (Na4 EDTA), and heated to different temperatures. Mixtures at 1:1 ratio of 5% NaOCl with distilled water (considered NaOCl alone), 18% HEDP or 10% Na4 EDTA were heated to 25°C, 37°C, 48°C and 60°C. The FAC in the mixtures was assessed at 5, 10, 20, 30, 60 and 120min. Samples of bovine muscle tissue (n=10) were prepared with similar size and weighed before and after 5, 10 and 15min of immersion in the mixtures heated to the different temperatures to verify organic matter dissolution. The intergroup results were compared statistically using one-way analysis of variance (anova) and intragroup by two-way analysis of variance (anova), both followed by Tukey's multiple-comparison test (α<0.01). Bovine dentine blocks (n=10) were analysed by scanning electron microscopy before and after immersion in the mixtures, and the time taken to remove the smear layer from the surfaces of the samples was determined. The Friedman test was used to compare the scores of the same group (α<0.01), and the Kruskal-Wallis test with Dunn's post hoc was used to compare the different groups (α<0.01). Saline solution was used as a control in the experiments of tissue dissolution and smear layer removal, RESULTS: Heating NaOCl alone did not affect its FAC. The higher the temperature of the mixtures with the chelators, the lower the FAC. Organic tissue dissolution was improved by increases in temperature of NaOCl alone and its mixture with HEDP (P<0.01); however, the mixture with Na4 EDTA had no improvement (P>0.01). Smear layer removal by NaOCl alone was enhanced by heating resulting in lower scores in some samples and became more rapid in the mixtures with the chelators. The saline solution did not promote tissue dissolution nor smear layer removal (P>0.01). In this laboratory study, heating NaOCl alone or when mixed with HEDP improved its capacity to dissolve organic matter and remove the smear layer. However, the mixture with HEDP required frequent refreshment to retain these effects when heated. Due to the acceleration in the reaction between the irrigants, very rapid reductions in the free available chlorine in the mixtures with Na4 EDTA heated to the different temperatures occurred.

Oxidation of Selected Trace Organic Compounds through the Combination of Inline Electro-Chlorination with UV Radiation (UV/ECl2) as Alternative AOP for Decentralized Drinking Water Treatment

A large variety of Advanced Oxidation Processes (AOPs) to degrade trace organic compounds during water treatment have been studied on a lab scale in the past. This paper presents the combination of inline electrolytic chlorine generation (ECl2) with low pressure UV reactors (UV/ECl2) in order to allow the operation of a chlorine-based AOP without the need for any chlorine dosing. Lab studies showed that from a Free Available Chlorine (FAC) concentration range between 1 and 18 mg/L produced by ECl2 up to 84% can be photolyzed to form, among others, hydroxyl radicals (OH) with an UV energy input of 0.48 kWh/m3. This ratio could be increased to 97% by doubling the UV energy input to 0.96 kWh/m3 and was constant throughout the tested FAC range. Also the achieved radical yield of 64% did not change along the given FAC concentration range and no dependence between pH 6 and pH 8 could be found, largely simplifying the operation of a pilot scale system in drinking water treatment. Whereas with ECl2 alone only 5% of benzotriazoles could be degraded, the combination with UV improved the degradation to 89%. Similar results were achieved for 4-methylbenzotriazole, 5-methylbenzotriazole and iomeprol. Oxipurinol and gabapentin were readily degraded by ECl2 alone. The trihalomethanes values were maintained below the Germany drinking water standard of 50 µg/L, provided residual chlorine concentrations are kept within the permissible limits. The here presented treatment approach is promising for decentralized treatment application but requires further optimization in order to reduce its energy requirements.

Chlorination and bromination of olefins: Kinetic and mechanistic aspects

Hypochlorous acid (HOCl) is typically assumed to be the primary reactive species in free available chlorine (FAC) solutions. Lately, it has been shown that less abundant chlorine species such as chlorine monoxide (Cl2O) and chlorine (Cl2) can also influence the kinetics of the abatement of certain organic compounds during chlorination. In this study, the chlorination as well as bromination kinetics and mechanisms of 12 olefins (including 3 aliphatic and 9 aromatic olefins) with different structures were explored. HOCl shows a low reactivity towards the selected olefins with species-specific second-order rate constants <1.0 M−1s−1, about 4-6 orders of magnitude lower than those of Cl2O and Cl2. HOCl is the dominant chlorine species during chlorination of olefins under typical drinking water conditions, while Cl2O and Cl2 are likely to play important roles at high FAC concentration near circum-neutral pH (for Cl2O) or at high Cl− concentration under acidic conditions (for Cl2). Bromination of the 12 olefins suggests that HOBr and Br2O are the major reactive species at pH 7.5 with species-specific second-order rate constants of Br2O nearly 3-4 orders of magnitude higher than of HOBr (ranging from <0.01 to >103 M−1s−1). The reactivities of chlorine and bromine species towards olefins follow the order of HOCl < HOBr < Br2O < Cl2O ≈ Cl2. Generally, electron-donating groups (e.g., CH2OH- and CH3-) enhances the reactivities of olefins towards chlorine and bromine species by a factor of 3-102, while electron-withdrawing groups (e.g., Cl-, Br-, NO2-, COOH-, CHO-, -COOR, and CN-) reduce the reactivities by a factor of 3-104. A reasonable linear free energy relationship (LFER) between the species-specific second-order rate constants of Br2O or Cl2O reactions with aromatic olefins and their Hammett σ+ was established with a more negative ρ value for Br2O than for Cl2O, indicating that Br2O is more sensitive to substitution effects. Chlorinated products including HOCl-adducts and decarboxylated Cl-adduct were identified during chlorination of cinnamic acid by high-performance liquid chromatography/high resolution mass spectrometry (HPLC/HRMS).

Acidic electrolyzed water potently inactivates SARS-CoV-2 depending on the amount of free available chlorine contacting with the virus

Alcohol-based disinfectant shortage is a serious concern in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Acidic electrolyzed water (EW) with a high concentration of free available chlorine (FAC) shows strong antimicrobial activity against bacteria, fungi, and viruses. Here, we assessed the SARS-CoV-2-inactivating efficacy of acidic EW for use as an alternative disinfectant. The quick virucidal effect of acidic EW depended on the concentrations of contained-FAC. The effect completely disappeared in acidic EW in which FAC was lost owing to long-time storage after generation. In addition, the virucidal activity increased proportionately with the volume of acidic EW mixed with the virus solution when the FAC concentration in EW was same. These findings suggest that the virucidal activity of acidic EW against SARS-CoV-2 depends on the amount of FAC contacting the virus.

Destruction of Cyanide and Removal of Copper from Waste Printed Circuit Boards Leach Solution Using Electro-Generated Hypochlorite Followed by Magnetite Adsorption

The removal of the cyanide and copper (Cu) from the waste printed circuit boards (WPCBs) cyanide leach solution through the alkaline chlorination using electro-generated hypochlorite (NaOCl) followed by magnetite (Fe3O4) adsorption is investigated. The efficiency of the destruction of cyanide and precipitation of Cu was increased with increasing the concentration of free available chlorine in NaOCl. More than 99% of free cyanide and 76% of Cu were removed under the following conditions: concentration of chlorine in electro-generated NaOCl, 5.2 g/L; volume ratio of NaOCl/leach solution, 1; pH, ~9.8; ambient temperature for 12 h. Then, magnetite adsorption for selective removal of remaining Cu (50.5 mg/L) was selected and more than 99% of copper ion was successfully removed with dosage 10g/100mL, shaking speed 150 rpm within 30 min. The results revealed that the alkaline chlorination using electro-generated NaOCl followed by magnetite adsorption could completely remove the cyanide and Cu, remaining Au in the final solution.

Difference between the Actual and Labeled Concentrations of Several Domestic Brands of Sodium Hypochlorite.

Sodium hypochlorite (NaOCl) is extensively used in root canal treatment and its efficacy depends on the concentration of free available chlorine (FAC). This study aimed to assess the chlorine content of 10 domestically manufactured household bleach products available in the Iranian market and evaluate the effect of temperature, time and daily bottle uncapping on FAC concentration and pH of these products. One-liter bottles of 10 available brands of household bleach (n=4 of each brand) were collected and randomly divided into four groups (n=10). Two groups were refrigerated at 4°C while the remaining two were stored at room temperature. One group of refrigerated and one group of room temperature samples were subjected to daily bottle uncapping followed by agitation and recapping for 3 months (six times a week to simulate weekly office work). The remaining bottles remained untouched and served as controls. The concentration of FAC in each sample was measured using the iodometric titration assay, and the pH was measured using a calibrated pH-meter at baseline and 1, 2 and 3 months. The results were analyzed using the one-way ANOVA and t-test. The mean concentration of FAC in the solutions was 4.87±0.19% at baseline. The measured concentration of sodium hypochlorite was different from the labeled value. The concentration of FAC decreased over time in all samples; the greatest reduction occurred in room temperature samples subjected to daily uncapping while the smallest reduction occurred in refrigerated, capped bottles (19% and 1.9%, respectively). The pH of all products decreased over time. The mean reduction in pH was 1.1 for the samples stored at room temperature for 3 months and 0.8 for the refrigerated samples. This in vitro study showed that the expected concentration of sodium hypochlorite solution made of household bleach for endodontic purposes is different from its actual concentration.

Influence of Ammonium Ions, Organic Load and Flow Rate on the UV/Chlorine AOP Applied to Effluent of a Wastewater Treatment Plant at Pilot Scale.

This work investigates the influence of ammonium ions and the organic load (chemical oxygen demand (COD)) on the UV/chlorine AOP regarding the maintenance of free available chlorine (FAC) and elimination of 16 emerging contaminants (ECs) from wastewater treatment plant effluent (WWTE) at pilot scale (UV chamber at 0.4 kW). COD inhibited the FAC maintenance in the UV chamber influent at a ratio of 0.16 mg FAC per mg COD (kHOCl–COD = 182 M−1s−1). An increase in ammonium ion concentration led to a stoichiometric decrease of the FAC concentration in the UV chamber influent. Especially in cold seasons due to insufficient nitrification, the ammonium ion concentration in WWTE can become so high that it becomes impossible to achieve sufficiently high FAC concentrations in the UV chamber influent. For all ECs, the elimination effect by the UV/combined Cl2 AOP (UV/CC) was not significantly higher than that by sole UV treatment. Accordingly, the UV/chlorine AOP is very sensitive and loses its effectiveness drastically as soon as there is no FAC but only CC in the UV chamber influent. Therefore, within the electrical energy consumption range tested (0.13–1 kWh/m3), a stable EC elimination performance of the UV/chlorine AOP cannot be maintained throughout the year.

Development of a portable electrolytic sanitising unit for the production of neutral electrolysed water

The aim of this study was to develop and evaluate the characteristics and performance of a portable electrolytic sanitising unit. Free available chlorine (FAC), oxidation-reduction potential, and pH of electrolysed water were measured. Response surface methodology coupled with a Box-Behnken design was used to describe the input-output relationship and optimise FAC production. A partial catholyte solution was reintroduced to electrolysis for generating neutral electrolysed water. The result found that RuO2-IrO2/TiO2 electrode was very effective. A FAC concentration of 4 mg/L achieved >2 log CFU/mL reduction, while a FAC concentration of 40 mg/L achieved >6 log CFU/mL reduction in Escherichia coli O157:H7 and Listeria monocytogenes BAA-839. The developed sanitiser had a pH of 7.08 ± 0.08, and the commercial sanitiser had a pH of 3.77 ± 0.18. The developed sanitiser had similar bactericidal effects as the commercial sanitiser. The results revealed that the developed sanitising unit is promising for the control of foodborne pathogens.

Removal of carbamazepine in aqueous solutions through solar photolysis of free available chlorine

Removal of a persistent antiepileptic drug carbamazepine (CBZ) in aqueous solutions was investigated by using solar photolysis combined with free available chlorine (FAC). The combination of chlorination with simulated or natural sunlight markedly enhanced removal of CBZ in 10 mM phosphate buffer solution (pH 7.0) and river water (pH 7.0) compared with sunlight or FAC alone. Further analysis indicated that the observed enhancements in CBZ removal can be attributed to the in situ hydroxyl radical (HO) and ozone (O3) production during FAC photolysis. During 70 min simulated sunlight photolysis combined with FAC treatment, HO reaction contributed to 35.8% removal of CBZ and O3 reaction contributed to 40.6% removal, while only 5.3% of CBZ was removed by HOCl reaction. The oxidation products of CBZ, epoxide CBZ, 10,11-dihydro-10,11-dihydroxy CBZ, 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM), 1-(2-benzaldehyde)-(1H,3H)-quinazoline-2,4-dione (BQD) and 4-aldehyde-9-acridone, were mainly formed from the HO and O3 attack at the double bond on the central heterocyclic ring of CBZ. Formation of these oxidation products did not cause any increase or decrease in toxicity to microbial species tested through Microbial Assay for Toxicity Risk Assessment (MARA). The initial FAC concentration and pH had a major influence on the removal process of CBZ during FAC photolysis, while temperature had a minor effect only. The combination of chlorination with natural sunlight could provide an effective approach for removal of CBZ and other contaminants during water treatment.

Rapid treatment of vessels fouled with an invasive polychaete, Sabella spallanzanii, using a floating dock and chlorine as a biocide

Chlorine solution was added to the water encapsulated within a proprietary ‘floating dock’ to treat a vessel infested with the invasive polychaete Sabella spallanzanii. The chlorine was added as sodium dichloroisocyanurate (‘dichlor’) at an initial concentration of 200 mg l−1 of free available chlorine (FAC). This concentration killed 99% of S. spallanzanii in their tubes during a 4-h exposure in laboratory tests (EC99 160 mg FAC l−1). The concentration of FAC in the floating dock declined to ~50 mg l−1 after 4 h and < 10 mg l–1 after 16 h. Residual FAC was neutralised with thiosulphate at completion of exposure. A sample of 30 S. spallanzanii individuals collected from the hull after treatment all showed morphological damage and 28 showed no response to touch. Re-examination of the hull after 6 d found no live worms or other fouling organisms. This method provides a cost-effective, rapid means of treating hull fouling.

Inactivation of Vibrio parahaemolyticus Unattached and Attached to a Solid Surface in pH-Controlled Sodium Hypochlorite Solutions.

The inactivation of Vibrio parahaemolyticus cells that were unattached or attached to a polyethylene terephthalate (PET) disc in pH-controlled sodium hypochlorite (NaOCl) solutions was studied under turbulent conditions. No significant desorption of attached cells occurred at the free available chlorine (FAC) concentrations from 0.1 to 1.0 mg/l. The number of viable cells was estimated by microbial calorimetry. The logarithmic relative reduction of viable cells was proportional to the product of the FAC concentration and time. In the pH range of 5.6 to 9.3, the first-order inactivation rate constants for unattached and attached cells increased with decreasing solution pH. It was found that the rate constants for unattached cells were approximately 6 to 7 times higher than those for attached cells at all pH values examined. It was confirmed that attached cells were more resistant to NaOCl solutions than unattached cells even when accessibility of attached cells to HOCl/OCl- was enhanced under turbulent conditions.

An Evaluation of the Accuracy of Labeling of Percent Sodium Hypochlorite on Various Commercial and Professional Sources: Is Sodium Hypochlorite from These Sources Equally Suitable for Endodontic Irrigation?

IntroductionThe shelf life of sodium hypochlorite (NaOCl) is limited, and a previous article showed that there can be a discrepancy between the expected concentration of free available chlorine (FAC) and the actual FAC concentration in NaOCl solutions intended for endodontic irrigation. The current study investigates the FAC content of domestic and professional NaOCls and evaluates the influences of dilution and storage on FAC concentration. MethodsFirst, domestic and professional NaOCls not obtained from manufacturers were iodometrically titrated. Then, NaOCls were diluted with demineralized water or tap water and stored at 4°C or 18°C and analyzed at baseline and 2 and 22 weeks. Statistical analyses included paired samples, independent samples t tests and repeated multivariate analysis of variance. Correlations were calculated with the Pearson or Spearman rank correlation test. A P < .05 was considered significant. ResultsLabel specifications of domestic NaOCl were very imprecise (ie, <5% NaOCl). Domestic NaOCl contained 1.8%–3.5% NaOCl (w/v). Professional NaOCl varied from 14.3% relative less FAC than specified on the label to 23.5% relative more FAC than specified. After 22 weeks, the relative average loss of FAC in all conditions was 5.4% FAC (P = .002). Dilution, diluents, or storage temperature had no effect on the decline of FAC caused by aging. ConclusionsThere is a great variation in NaOCl concentrations, with domestic NaOCl being the least accurate. NaOCl can be stored up to 5 months. The FAC concentration of domestic NaOCl is unpredictable, and, therefore, it appears less suitable for clinical application as root canal irrigant.

Free available chlorine concentration in sodium hypochlorite solutions obtained from dental practices and intended for endodontic irrigation: are the expectations true?

Sodium hypochlorite (NaOCl) is an important tool in root canal disinfection although it is well known that the shelf-life of NaOCl is limited. In this study, NaOCl solutions that were collected from dental practices and were intended for endodontic irrigation were investigated to see whether they contained the expected concentration of free available chlorine. NaOCl solutions were collected from dental practices. The concentration of available chlorine per sample was determined with iodometric titration and the pH was measured. Each participating dentist completed a questionnaire that requested data on a range of issues relating to the assumed concentration of NaOCl and handling of the sample. Eighty-four samples with questionnaires were received. NaOCl was purchased from supermarkets and drugstores (36%), dental suppliers (48%), or pharmacies (16%). The median expected concentration was 2% (n = 36). On average, 27% less available chlorine was measured than the dentist assumed was in the sample (P < .001). Fifteen percent of samples contained less than 1% available chlorine, which is needed for tissue dissolution and disinfection. The average pH was 11.5. The greatest differences in concentrations were found in NaOCl sourced from supermarkets or drugstores. Future studies should elucidate the cause of this discrepancy. In the meantime it is recommended to purchase NaOCl from professional suppliers, because this group showed the most reliable content of free available chlorine.

Virucidal effect of acidic electrolyzed water and neutral electrolyzed water on avian influenza viruses

The virucidal effects of two types of electrolyzed water, acidic electrolyzed water (AEW) and neutral electrolyzed water (NEW), on avian influenza viruses were studied. Virus titers of the highly pathogenic H5N1 virus and the low-pathogenic H9N2 virus irreversibly decreased by >5-log at 1min after the viruses were mixed with NEW containing ≥43ppm free available chlorine (FAC), but not with NEW containing <17ppm FAC. The minimum concentration of FAC for a virucidal effect of NEW was estimated at around 40ppm. In contrast, the virus titers decreased by >5 log at 1min after the viruses were mixed with AEW, in which the concentration of the FAC ranged from 72 to 0ppm. Thus, the virucidal effect of AEW did not depend on the presence of FAC. Reverse transcription polymerase chain reaction amplified fragments of the M and NP genes, but not the complete M gene, from RNA extracted from the AEW-inactivated virus. Moderate morphological changes were found under the electron microscope, although no changes were observed in the electrophoresed proteins of the AEW-inactivated virus. No viral genes were amplified from the RNA extracted from the NEW-inactivated virus, regardless of the length of the targeted genes. No viral particles were detected under the electron microscope and no viral proteins were detected by electrophoresis for the NEW-inactivated virus. Thus, this study demonstrated potent virucidal effects of AEW and NEW and differences in the virucidal mechanism of the two types of electrolyzed water.

Inactivation efficiency to Bacillus subtilis and Escherichia coli bacterial aerosols of spraying neutral electrolyzed water

The main objective of this study is to apply neutral electrolyzed water (NEW) spraying to inactivate bioaerosols. We evaluated the inactivation efficiency of NEW applied to inactivate two airborne bacterial Escherichia coli and Bacillus subtilis aerosols inside an environmental-controlled chamber in the study. Generated with electrolyzing 6.15 M sodium chloride brine, the NEW with free available chlorine (FAC) concentration 50, 100, and 200 ppm was pumped with an air pressure of 70 kg/cm2 through nozzle into the chamber to inactive E. coli and B. subtilis aerosols precontaminated air (initial counts of 3 × 104 colony-forming units [CFU]/m3). Bacterial aerosols were collected and cultured from chamber before and after NEW spray. The air exchange rate (ACH, hr−1) of the chamber was set to simulate fresh air ventilating dilution of indoor environment. First-order concentration decaying coefficients (Ka, min−1) of both bacterial aerosols were measured as an index of NEW inactivation efficiency. The result shows that higher FAC concentration of NEW spray caused better inactivation efficiency. The Ka values under ACH 1.0 hr−1 were 0.537 and 0.598 for E. coli of FAC 50 and 100 ppm spraying, respectively. The Ka values of FAC 100 ppm and 200 ppm spraying for B. subtilis were 0.063 and 0.085 under ACH 1.0 hr−1, respectively. The results indicated that NEW spray is likely to be effective in inactivation of bacterial airborne contamination. Moreover, it is observed in the study that the increase of ventilation rate and the use of a larger orifice-size nozzle may facilitate the inactivation efficiency. Implications: Bacterial aerosols have been implicated in deterioration of air quality and occupational health. Effective, safe, and economic control technology is highly demanded, especially for agricultural and food industries. In the study, NEW mist spraying performed effectively in controlling E. coli and B. subtilis modeling bioaerosols contamination. The NEW revealed its potential as an alternative airborne disinfectant worth being discovered for improving the environmental quality in the future.

Oxidative scrubbing of DMS-containing waste gases by hypochlorite solution

Biological units treating wastewater containing dimethyl sulfoxide (DMSO) emit odorous dimethyl sulfide (DMS). This study investigated possible solutions for the odor problem of DMS emitted from wastewater units in the thin-film transistor–liquid crystal displayer (TFT–LCD) and semiconductor manufacturing industries. The study focused on the liquid-phase oxidation of DMS and oxidative scrubbing of DMS-containing gas using hypochlorite as an oxidant. Results showed that liquid phase reaction of aqueous DMS (initial DMS 29.1–106mg/L) by aqueous hypochlorite solution (initial Cl2 71.0–182mg/L) rapidly converted all the DMS to stable dimethyl sulfone (DMSO2), using stoichiometric available chlorine at a pH of 7 or 8. At pH 10, approximately 50% of the DMS was oxidized to DMSO2, indicating the limited oxidative ability of hypochlorite in an alkaline solution. With sufficient available chlorine (initial available chlorine 92–102mg/L), the rate-limiting step for gas-borne DMS (31–177ppm) scrubbing was the mass transfer of DMS to the solution, rather than the oxidation of DMS. Complete oxidation of the absorbed DMS was observed in scrubbing liquids with a pH of 7, 8, and 10 because of the higher concentration of free available chlorine in the liquid compared with the limited absorbed DMS. The tested field scrubber removed almost all DMS at approximately 250–930ppm in the influent gas, with the scrubbing liquid maintained at an ORP of 850–900mV and pH of 6.5–7.0.

Applying the Membrane-Less Electrolyzed Water Spraying for Inactivating Bioaerosols

The inactivating efficiency using membrane-less electrolyzed water (MLEW) spraying was evaluated against two airborne strains, Staphylococcus aureus and λ virus aerosols, in an indoor environment-simulated chamber. The air exchanged rate (ACH) of the chamber was controlled at 0.5 and 1.0 h–1. MLEW with a free available chlorine (FAC) concentrations of 50 and 100 ppm were pumped and sprayed into the chamber to treat microbial pre-contaminated air. Bioaerosols were collected and cultured from air before and after MLEW treatment. The first-order constant inactivation efficiency of the initial counts of 3 × 104 colony-forming units (CFU or PFU)/m3 for both microbial strains were observed. A higher FAC concentration of MLEW spraying resulted in greater inactivation efficiency. The inactivation coefficient under ACH 1.0 h–1 was 0.481 and 0.554 (min–1) for Staphylococcus aureus of FAC 50 and 100 ppm spraying. In addition, increasing the air exchange rate also improved the inactivation rate. The inactivation coefficient of FAC 100 ppm spraying for Staphylococcus aureus was 0.412 and 0.403 (min–1) under ACH 1.0 and 0.5 h–1. These results indicated that MLEW spraying is likely to be effective in minimizing microbial airborne contamination, especially for poorly ventilated spaces.