Free Chlorine Concentration Research Articles

Chloride binding mechanism and free chloride reduction method of alkali-activated slag/fly ash mixed with seawater

The chloride binding mechanism of alkali-activated materials (AAM) under various granulated blast furnace slag (GBFS)/fly ash (FA) ratios is investigated in this work. Two types of layered double hydroxides (LDH), i.e., MgAl-LDH and CaAl-LDH, and active magnesium oxide (MgO) were added to reduce the concentration of free chloride in AAM. The results demonstrate that the ratio of GBFS to FA has non-negligible influence on the AAM’s ability to bind chloride. The content of bound chloride increased by 3.78%-17.42% as the FA content in seawater-based alkali-activated materials (SAAM) raised. The chloride binding forms of SAAM were mainly chemical binding by the hydrated calcium aluminate (AFm) phase and physical adsorption by calcium (alumino) silicate hydration (C-(A)-S-H) gels when the FA dosage is less than 20% in SAAM. When the FA mass ratio in SAAM was larger than 20%, the chloride binding form of SAAM was mainly the physical adsorption by calcium (sodium)alumino-silicatehydrate ((C,N)-A-S-H) gels. Among the three additive materials, CaAl-LDH was the most effective in reducing the free chlorine content by 11.34%. While for MgAl-LDH, the chloride binding capacity was compromised by the less strength loss. In this work, seawater was used as the mixing water to introduce chloride ions, the results of which could provide a reference for the application of seawater in future projects.

Effect of ferric salt addition on UV/electro-chlorine advanced oxidation process

ABSTRACT This study discussed the effect of ferric salt addition on UV/electro-chlorine advanced oxidation process using a train of electrolytic and UV flow cells with an ozone-free low-pressure mercury vapour lamp (total irradiance:0.60 W at 254 nm). Ferric salt addition enhanced 1,4-dioxane degradation at an electrolytic current of 0.100 A. By contrast, an inhibitory effect of ferric salt addition was observed at a current of 0.500 A. The enhanced accumulation of free chlorine at a current of 0.500 A directly decreased the 1,4-dioxane degradation rate by scavenging reactive radicals like HO˙ and Cl˙. However, at an electrolytic current of 0.100 A, UV irradiance was relatively excessive for electrochemical chlorine production. The excess UV energy enhanced the photoreduction of FeOH2+, followed by the Fenton-type reaction of Fe2+ and HOCl, which produced HO˙ and consumed free chlorine. As a result, the free chlorine concentration decreased, and the reaction efficiency between the reactive radicals and 1,4-dioxane improved. Thus, the addition of ferric salt to a UV/electro-chlorine system is recommended when the UV irradiance in the system is excessive compared to the electrochemical chlorine supply.

Evaluation of water quality via determination of trihalomethanes in water distribution networks of Riyadh city in Kingdom of Saudi Arabia

Trihalomethane (THM) has been classified as a possible human carcinogen by the International Agency for Research on Cancer (IARC). This study was conducted to assess the levels of trihalomethane compounds in the Riyadh city water network in two different years (2015 and 2020) and to understand the factors affecting the formation of these compounds. The study covered 15 sites in Riyadh city, distributed between the north, south, east, west and middle of the city. The results of the study indicated that the sum of the ratio of the concentration of each THM compound to its respective World Health Organization(WHO) guideline value not exceed 1 (unitless) where the combined toxicity of all total trihalomethanes THMs concentrations did not exceed the permissible limits, with values ranging between 0.01 and 0.24 at all study sites. These results were less than the recommended guide values form WHO for individual maximum concentrations of each of the THM in water for human consumption. In addition, the average concentration of free chlorine was 0.04 ppm and 0.09 ppm in 2015 and 2020, respectively, indicating that the disinfection had evolved in 2020 compared to 2015. Moreover, there was a weak relationship between trihalomethane formation and the presence of bromide ions and organic carbon, whereas a positive correlation was observed with free chlorine and pH values. The concentration of heavy metals such as cadmium, arsenic, cobalt and chromium were analysed by inductively coupled plasma-optical emission spectroscopy. The results indicated that all heavy metals were within the standard limits: the maximum values were 123 ppb in 2015 and 70.39 ppb in 2020, with lead having the lowest concentration and aluminium having the highest concentration in both years. Furthermore, the ion chromatography results of the cations (sodium Na±, potassium K±, calcium Ca2+and magnesium Mg2+) and the anions (fluoride F-, bromide Br-, chloride Cl-, sulphate SO42- and nitrate NO3–) indicated that the water in this study was suitable for human consumption based on the WHO regulation and the Ministry of Environment, Water and Agriculture (MEWA) standards for drinking water.

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 the antibiotic ciprofloxacin in urine by electrochemical oxidation with a DSA anode

Ciprofloxacin (CIP) is a commonly prescribed fluoroquinolone antibiotic that, even after uptake, remains unmetabolized to a significant extent—over 70%. Unmetabolized CIP is excreted through both urine and feces. This persistent compound manages to evade removal in municipal wastewater facilities, leading to its substantial accumulation in aquatic environments. This accumulation raises concerns about potential risks to the health of various living organisms. Herein, we present a study on the remediation of CIP in synthetic urine by electrochemical oxidation in an undivided cell with a DSA (Ti/IrO2) anode and a stainless-steel cathode. Physisorbed hydroxyl radical formed at the anode surface from water discharge and free chlorine generated from Cl− oxidation were the main oxidizing agents. The effect of pH and current density (j) on CIP degradation was examined, and its total removal was easily achieved at pH ≥ 7.0 and j ≥ 60 mA cm−2 due to the action of free chlorine. The CIP decay always followed a pseudo-first-order kinetics. The components of the synthetic urine were also oxidized. The main nitrogenated species released was NH3. A very small concentration of free chlorine was quantified at the end of the treatment, thus demonstrating the good performance of electrochemical oxidation and its effectiveness to destroy all the organic pollutants. The present study demonstrates the simultaneous oxidation of the organic components of urine during CIP degradation, thus showing a unique perspective for its electrochemical oxidation that enhances the environmental remediation strategies.

Effect and influence mechanism of biofilm formation on the biological stability of reclaimed water

Microorganisms and sediments in reclaimed water adhere to the inner walls of pipes or water tanks, forming biofilms that support the continuous growth of microorganisms. These biofilms provide a protective barrier, shielding bacteria from disinfectants. This study investigated the impact of biofilms on bacterial growth and reproduction in reclaimed water and the factors limiting bacterial growth in reclaimed graywater (GMR) and reclaimed mixed wastewater (MWR). The results revealed that biofilm biomass gradually increased and reached a maximum value on Days 20–25, and the biomass of organisms continued to decrease after 40 days. Biofilms serve as a source of bacteria, continuously releasing them into reclaimed water systems. The presence of biofilms reduced the biological stability of the reclaimed water, leading to water quality deterioration. The concentration of assimilable organic carbon in the reclaimed water showed a positive correlation with the heterotrophic bacterial count and Escherichia coli levels in both the reclaimed water and biofilms. The threshold value of chlorine for inhibiting biofilms in reclaimed water was no <2 mg/L. High concentrations of free chlorine delayed the growth of biofilms but did not reduce the final biomass generated by the biofilms. Carbon was the limiting factor for the biological stability of reclaimed water, while nitrogen, phosphorus, and inorganic salts were not limiting factors. Thus, minimizing the concentration of organic matter in reclaimed water can reduce the nutrient sources available for biofilm formation. This study provides support for advancements in the wastewater reuse industry.

Formation of reactive chlorine species in Cl− solutions treated by plasma-supplied O atoms and some implications for biological inactivation functions

Plasma activated saline solution (PAS) has attracted increased attention in recent years due to wide range of promising applications including sterilization, water treatment, wound healing, and cancer treatment. As we know, reactive oxygen and nitrogen species (RONS) play an important role in plasma applications and its production and action mechanisms have been intensively studied. However, less attention has been paid to the role of reactive chlorine species (RCS). Therefore, researching the mechanism underlying the RCS formation in O-treated saline is necessary to regulate the RCS dose for improving plasma applications. In this work, the concentration of free chlorine (Cl2, HClO, ClO−) are focused to investigate the effect of the addition of Cl− and O2. Results show that the presence of chlorine in solutions, oxygen radicals in plasma jet and the pH of the solution are important factors in the further chemical reactions to RCS. The production of RCS and RONS can be selectively regulated by controlling the three conditions described above. Furthermore, some implications for biological inactivation functions are performed by the A549 lung carcinoma cells to verify the anticancer effects induced by PAS. Schematic of plausible mechanisms of the aqueous chemical processes in solutions are speculated by experimental results. These results provide new insight into the mechanism of chemical activity of PAS, which in turn promotes its more effective biomedical effects.

Model Development for Residual Chlorine

The research is to develop a mathematical model for the decay of residual chlorine at the nodes and compare with results from Epanet 2.0. All the influencing parameters of initial chlorine Ccl(init(o)), bulk decay (Kb), wall decay (KW) and travel time (t), were well represented and the equation is developed applying the differential form of the first order chlorine decay model, describing reactions occurring in the bulk fluid and at the pipe wall, which was transformed in to chlorine concentration-based integral expression Ccl (t) =Ccl (o).e-kt , is the free chlorine (HOCL) concentration (mg/l) at time (t), which is also called the residual chlorine. is the chlorine concentration at time zero, which is the initial chlorine concentration in the entire water distribution systems. KW is the pipe wall decay coefficient of the particular water distribution pipe network directly affected by initial concentration. K is expressed in the study as the decay due to the quality of water, known as bulk decay coefficient (kb), per unit hour (t=1) at any particular node per hour. he developed mathematical model was a reflection of the reality in the study area Rcl (n)=Ccl (init). KW. е-Kb . The results of the model at nodes 31, 12, 13, 14, 18, 10, 17, 15, 20 and 21 are 0.18 mg/l, 0.19 mg/l, 0.19 mg/l, 0.19 mg/l, 0.19 mg/l, 0.19 mg/l, 0.20 mg/l, 0.19 mg/l, 0.20 mg/l, 0.19mg/l, respectively. Epanet 2.0 results for the same nodes were determine to be 0.17 mg/l, 0.21 mg/l, 0.22 mg/l, 0.20 mg/l, 0.21 mg/l, 0.21 mg/l, 0.25 mg/l, 0.24 mg/l, 0.20 mg/l, 0.20 mg/l, 0.18 mg/l. The correlation between the developed mathematical model residual chlorine results and Epanet 2.0 results gives moderate correlation of 0.561, signifying 60% pearson correlation and 0.01, 2-tailed significance level at 99%.

Factors affecting the leaching of micro and nanoplastics in the water distribution system

The role of the water distribution system (WDS) requires that it supply water of sufficient quality to households. Unregulated leaching of micro and nanoplastics from plastic pipes of the distribution system is therefore a cause for concern, particularly with the rise in research associating these plastic particles to adverse health impacts in living organisms. Within this study, four parameters (pH, free chlorine concentration, pipe material, and time) were varied in a pipe loop network to observe their effect on microplastic (MP) and nanoplastic (NP) leaching into the simulated distribution network. Results indicated an abundance of MPs/NPs in different shapes and sizes throughout the samples. Graphical trends illustrated that basic pH values contributed to a higher number of particles. Statistical analysis via analysis of variance (ANOVA) confirmed this observation and further showed interaction of chlorine dose and pH concentration (p-value = 0.000), and chlorine dose and pipe material (p-value = 0.038) was also significant to leaching. Numerically, polyethylene (PE) particles were the most abundant with a total of 15194 particles, followed by 12920 polypropylene random copolymer (PPR) particles and 12317 polyvinyl chloride (PVC) particles. It was also noticed that the number of particles decreased with time.© 2023 Elsevier Inc. All rights reserved.

Chlorine disinfection modifies the microbiome, resistome and mobilome of hospital wastewater – A nanopore long-read metagenomic approach

The aim of the present study was to analyze changes in the microbiome, resistome, and mobilome of hospital wastewater (HWW) induced by disinfection with chlorine compounds. Changes in bacterial communities and specific antibiotic resistance genes (ARGs) in HWW were determined with the use of a nanopore long-read metagenomic approach. The main hosts of ARGs in HWW were identified, and the mobility of resistance mechanisms was analyzed. Special attention was paid to the prevalence of critical-priority pathogens in the HWW microbiome, which pose the greatest threat to human health. The results of this study indicate that chlorine disinfection of HWW can induce significant changes in the structure of the total bacterial population and antibiotic resistant bacteria (ARB) communities, and that it can modify the resistome and mobilome of HWW. Disinfection favored the selection of ARGs, decreased their prevalence in HWW, while increasing their diversity. The mobility of the HWW resistome increased after disinfection. Disinfection led to the emergence of new drug resistance mechanisms in previously sensitive bacterial taxa. In conclusion, this study demonstrated that HWW disinfected with low (sublethal) concentrations of free chlorine significantly contributes to the mobility and transfer of drug resistance mechanisms (including critical mechanisms) between bacteria (including pathogens).

The impact of chlorine, ultraviolet-C, and microwave treatment on the survivability of Blastocystis sp. cysts.

Blastocystis sp. is a common widely distributed gut protozoan, with water transmission identified as one of its transmission routes. This study aimed to investigate the effect of chlorine, ultraviolet (UV)-C, and microwave (MW) treatments on the in vitro viability of cysts of Blastocystis sp. Purified Blastocystis sp. cysts were molecularly subtyped. Viable cysts were subjected to different free chlorine concentrations (1, 2, and 4 ppm), different doses of UV-C (5.13, 10.26, 20.52, and 40.47 mJ/cm2), and MW irradiation times (10, 15, 30, and 45 s). Viability reduction percentage, log10 inactivation, and micrometre-based optical microscopy examined cyst number and appearance after each disinfection trial. The three disinfectants' efficacy and application conditions were assessed. The analysed isolates of Blastocystis cysts were subtype 3, possessed varying sizes and shapes, but two identical genomes. The cysts of Blastocystis sp. were resistant to chlorine at all doses and exposure durations tested. UV-C at a dose of 40 mJ/cm2 and MW treatment for 15 s were able to completely disinfect the cysts. The MW was the most effective disinfectant against Blastocystis cysts based on all evaluated factors. MW irradiation is the most efficient water treatment method for eradicating Blastocystis cysts in an easy and safe manner.

Transformation behavior of the ultraviolet absorbent 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) in polyethylene plastic under chlorination

In plastic, a 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) ultraviolet light absorber is a common additive. When using sodium hypochlorite (NaClO) to disinfect plastic, UV328 may react with NaClO. For this work, we investigated the transformation behavior of UV328 in polyethylene (PE) plastic by NaClO. The reaction rate increased with the initial free active chlorine (OCl−) concentration and the decrease of the initial UV328 concentration. At room temperature (25 °C) to lower temperatures (0 °C), OCl− could transform UV328, and the reaction activation energy was fitted as 31.10 kJ/mol. Replacement of the plastic carrier (change to polypropylene) had no effect on the reaction process. A total of 12 intermediates were identified, and calculations based on density functional theory (DFT) were used to assist in rationalizing the product structure. Chlorination, hydroxylation, coupling, and bond cleavage were speculated as the main transformation pathways. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were the only two measured disinfection by-products in the system, and their concentration were 18.33 and 18.19 μg/g, respectively. The toxicity prediction by Toxicity Estimation Software Tool (T.E.S.T) illustrated that the toxicity of the transformation products was higher overall than that of UV328 during the reaction. This work can help to deepen the understanding of the transformation behavior of UV328 in PE plastic in NaClO solution.

AUTOMATION OF CHLORINE DOSAGE ADJUSTMENT CALCULATION IN DEEP TUBULAR WATER WELLS USING A JAVASCRIPT AND HTML SCRIPT

Background: Chlorine, in the form of sodium hypochlorite (NaClO), is widely used in water treatment to make it safe for human consumption. There are three main forms of chlorine: chlorine gas (Cl2), sodium hypochlorite (NaClO), and calcium hypochlorite. All are effective in water disinfection. Chlorine dosage is controlled to eliminate pathogenic microorganisms without exceeding safe limits for human consumption, aiming to avoid the use of excessive chlorine that can generate undesirable by-products. Measurement was carried out using DPD reagent to determine the concentration of free chlorine in the water. Aim: This work aims to facilitate the adjustment of chlorine dosage in water treatment, to reduce additional corrections. Methods: The Hach method 8021 was used to adjust chlorine dosage based on measurements of the interval between dosing pump pulsations and observed chlorine concentration. The concentration was adjusted from 1.68 mg/L to 1.20 mg/L. Additionally, the appropriate time for correct chlorine reading was determined, and the time needed for the corrected chlorine quantity to be observable in the system, adhering to the minimum limits set by legislation, was verified. Results: The adjustment of the initial chlorine concentration (1.66 mg/L) was carried out using the Hach method 8021, resulting in a stable concentration of approximately 1.19 mg/L. The desired dosage was 1.20 mg/L. The time required for correct chlorine measurement and observation of the corrected value was approximately 40 minutes. The use of the script allowed achieving a result 99.2% close to the planned value with just one adjustment. Discussion: The proper use of chlorine in water treatment is essential to ensure the safety and quality of supply. This research emphasized the need for careful monitoring of chlorine dosage, requiring time and accurate analysis of representative samples. The application of the developed script brought significant benefits, ensuring satisfactory disinfection and preventing overdosing issues. The results showed high efficacy and time savings, enhancing treatment efficiency and economic advantages. Moreover, the script reduced paper usage in calculations, promoting environmental sustainability. Conclusions: The script for adjusting the chlorine dosage used in water treatment made the operation more practical and efficient, with a user-friendly interface and accurate results achieved faster.

Virus purification highlights the high susceptibility of SARS-CoV-2 to a chlorine-based disinfectant, chlorous acid.

Chlorous acid water (HClO2) is known for its antimicrobial activity. In this study, we attempted to accurately assess the ability of chlorous acid water to inactivate SARS-CoV-2. When using cell culture supernatants of infected cells as the test virus, the 99% inactivation concentration (IC99) for the SARS-CoV-2 D614G variant, as well as the Delta and Omicron variants, was approximately 10ppm of free chlorine concentration with a reaction time of 10 minutes. On the other hand, in experiments using a more purified virus, the IC99 of chlorous acid water was 0.41-0.74ppm with a reaction time of 1 minute, showing a strong inactivation capacity over 200 times. With sodium hypochlorite water, the IC99 was 0.54ppm, confirming that these chlorine compounds have a potent inactivation effect against SARS-CoV-2. However, it became clear that when using cell culture supernatants of infected cells as the test virus, the effect is masked by impurities such as amino acids contained therein. Also, when proteins (0.5% polypeptone, or 0.3% BSA + 0.3% sheep red blood cells, or 5% FBS) were added to the purified virus, the IC99 values became high, ranging from 5.3 to 76ppm with a reaction time of 10 minutes, significantly reducing the effect. However, considering that the usual usage concentration is 200ppm, it was shown that chlorous acid water can still exert sufficient disinfection effects even in the presence of proteins. Further research is needed to confirm the practical applications and effects of chlorous acid water, but it has the potential to be an important tool for preventing the spread of SARS-CoV-2.

Batch and continuous bleaching regimen in the cooling tower of Montazer Ghaem power plant

In order to control the microbial growth in the cooling tower of thermal power plant, oxidative and non-oxidative biocides are applied in the power industry. Oxidative biocides including chlorine dioxide and bromine-based compounds are effective for controlling microbial growth in cooling towers. The choice of biocide depends on the type of cooling tower, water quality, and regulatory requirements. In the most cases, the bleaching regimen is selected as the most effective and low-cost oxidative biocides in cooling tower. The bleaching regimen is carried out in batch mode generally and herein for the first time, the continuous bleach is examined in the cooling tower of Montazer Ghaem power plant by evaluating the microbial growth. In the batch mode, 0.25 m3 of 12% bleach is injected into 1600 m3 every 3 days and in the continuous mode, the same amount (0.0035 m3/h) is continuously injected. The TBC11Total Bacteria Count in the cooling water before bleach, after batch and continuous bleach are 106, 104 and 103 cfu/mL, respectively. In fact, the performance of the continuous bleach is 10 times more efficient than the batch bleach. The physicochemical parameters including conductivity, NaCl%, TDS, pH, anions and cations concentration are not changed significantly and the chemical conditions are stable in both regimes which is proved that changing the bleach injection does not require the different chemical control. The free chlorine concentration in the continuous mode is constant (0.05 ppm) which is controlled the microbial growth and avoided the copper and iron corrosion.

Inactivation of Salmonella Typhimurium in fresh-cut lettuce during chlorine washing: Assessing the impacts of free chlorine concentrations and exposure times

The aim of this study was to evaluate, quantify and model the inactivation of Salmonella in fresh-cut lettuce during washings with chlorinated water at different free chlorine concentrations (FCC, 0–150 mg/L). Individual fresh-cut lettuce samples (4 cm2) were inoculated with a Salmonella culture (ca. 4 log CFU/cm2) and washed with 100-mL solutions with different FCC for different times (0–150 s). The surviving Salmonella cells recovered from samples were enumerated by plate count methodology. A fast decay on Salmonella counts was marked in the first 20 s of washing, followed by a slowing down on reductions. A maximum of 2.6 log-decrease was observed after 2.5-min washing regardless of FCC. The log-linear with tail primary model coupled with a linear secondary model was fitted to inactivation data obtained at FCC from 50 to 150 mg/L through global regression analysis, yielding a suitable model to describe Salmonella concentrations as a function of FCC and washing times (RMSE = 0.34, R2adj = 0.84). Simulations using the developed model showed inactivation rates varying from 0.17 log CFU/s at 50 mg/L to 0.86 log CFU/s at 150 mg/L. Disinfection models on lettuce are valuable tools for the validation of control measures in the fresh-cut produce industry and for quantitative risk assessments.

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.

Insight into the formation of polyhalogenated carbazoles during seawater chlorination

Although polyhalogenated carbazoles (PHCZs) have been widely detected in the marine environment, their origin is far from clear. In this study, the formation of PHCZs in the chlorination of seawater containing carbazole and its derivatives was investigated. A total of 14 PHCZs including six commonly found and eight unknown congeners were identified in the chlorination of seawater with carbazole. In addition, this study for the first time demonstrated the production of common PHCZs from the chlorination of seawater with 3-methyl carbazole and 3-formyl carbazole, especially 1,8-dibromo-3,6-dichlorocarbazole from 3-methyl carbazole. The formation of PHCZs in the reaction resulted from the halogenation of carbazole by reactive chlorine species (RCS) and mainly reactive bromine species (RBS), forming from the oxidation of bromide by RCS. Results also indicated that the reaction followed a successive halogenation pattern. A higher content of free chlorine and bromide facilitated the generation of RBS, while a higher concentration of DOC exhibited an inhibitory effect. The effects of free chlorine, bromide, DOC, and temperature on the formation of PHCZs were congener-specific. Given the widespread use of chlorination in seawater disinfection, seawater chlorination might be a potential source of PHCZs in the marine environment.

Investigation of removal and inactivation efficiencies of human sapovirus in drinking water treatment processes by applying an in vitro cell-culture system

Here, we examined the efficiencies of drinking water treatment processes for the removal and inactivation of human sapovirus (HuSaV). We applied a recently developed in vitro cell-culture system to produce purified solutions of HuSaV containing virus concentrations high enough to conduct virus-spiking experiments, to develop an integrated cell culture-polymerase chain reaction (ICC-PCR) assay to quantify the infectivity of HuSaV, and to conduct virus-spiking experiments. In virus-spiking coagulation-sedimentation–rapid sand filtration (CS–RSF) and coagulation–microfiltration (C–MF) experiments, HuSaV removals of 1.6–3.7-log10 and 1.2–>4.3-log10, respectively, were observed. The removal ratios observed with CS–RSF were comparable and correlated with those of murine norovirus (MNV, a widely used surrogate for human noroviruses) and pepper mild mottle virus (PMMoV, a potential surrogate for human enteric viruses in physical and physicochemical drinking water treatment processes), and those observed with C–MF were higher than but still correlated with those of MNV and PMMoV, indicating that MNV and PMMoV are both potential surrogates for HuSaV in CS–RSF and C–MF. For astrovirus (AstV, a representative human enteric virus), removal ratios of 1.8–3.3-log10 and 1.1–>4.0-log10 were observed with CS–RSF and C–MF, respectively. The removal ratios of AstV observed with CS–RSF were comparable and correlated with those of PMMoV, and those observed with C–MF were higher than but still correlated with those of PMMoV, indicating that PMMoV is a potential surrogate for AstV in CS–RSF and C–MF. When the efficacy of chlorine treatment was examined by using the developed ICC-PCR assay, 3.8–4.0-log10 inactivation of HuSaV was observed at a CT value (free-chlorine concentration [C] multiplied by contact time [T]) of 0.02 mg-Cl2·min/L. The infectivity reduction ratios of HuSaV were comparable with those of MNV. For AstV, 1.3–1.7-log10 and >3.4-log10 inactivation, as evaluated by ICC-PCR, was observed at CT values of 0.02 and 0.09 mg-Cl2·min/L, respectively. These results indicate that HuSaV and AstV are both highly sensitive to chlorine treatment and more sensitive than a chlorine-resistant virus, coxsackievirus B5 (1.3-log10 inactivation at a CT value of 0.4 mg-Cl2·min/L, as evaluated by the ICC-PCR assay).

ANALYSIS OF METHODS FOR DETERMINATION OF CHLORINE DIOXIDE, CHLORITE AND CHLORATE ANIONS IN DRINKING WATER

The analysis shows that the primary measure for the purification of drinking water is its reliable disinfection with oxidants, which are chlorine and its compounds, chlorine dioxide, ozone. The aim of the article is to analyze the existing methods for determination of chlorine dioxide, chlorite, hypochlorite and chlorate anions in drinking water. To analyze the chlorine dioxide strength solutions (to control the generator performance) the iodometric method (determination of chlorine dioxide concentration, concentration of free chlorine, chlorite and chlorate anions; relative error ≤ 5%) and the method of direct absorption at 445 nm (determination of chlorine dioxide concentration in the range of concentrations of 100-700 mg / l; relative error ≤ 2%) were used. To analyze the residual concentrations of chlorine dioxide, chlorite and hypochlorite anions in their joint presence the titrimetric and photometric methods with N,N-діетил-1,4-фенилендіамінсульфатом (DFD) (error of determination is of 0.05 mg/l) were used as well as iodometric method with photometric determination of iodine at 350 nm in the concentration range 0.01-0.5 mg/l. To analyze the residual concentrations of chlorine dioxide (selective methods), such methods were used: the photometric method with chlorophenol red in the concentration range of 0.02-0.7 mg/l; relative error ≤ 5%; photometric method with chromic violet acid in the concentration range of 0.1-1.5 mg/l. The method of ion chromatography was used to analyze the residual concentrations of chlorite and chlorate anions. Given the necessity for harmonization of domestic regulatory and guidance documentation with European one, it should be considered as necessary to control chlorites and chlorates in drinking water by method of ion chromatography. It is appropriate to conduct research on the approbation of ion chromatography method for the simultaneous determination of chlorites and chlorates in samples of water after its disinfection by various oxidants (sodium hypochlorite, ozone, chlorine dioxide).