Kinetics and mechanisms of non-radically and radically induced degradation of bisphenol A in a peroxymonosulfate-chloride system.

Bisphenol A, a hazardous endocrine disruptor, poses significant environmental and human health threats, demanding efficient removal approaches. Traditional biological methods struggle to treat BPA wastewater with high chloride (Cl-) levels due to the toxicity of high Cl- to microorganisms. While persulfate-based advanced oxidation processes (PS-AOPs) have shown promise in removing BPA from high Cl- wastewater, their widespread application is always limited by the high energy and chemical usage costs. Here we show that peroxymonosulfate (PMS) degrades BPA in situ under high Cl- concentrations. BPA was completely removed in 30 min with 0.3 mM PMS and 60 mM Cl-. Non-radical reactive species, notably free chlorine species, including dissolved Cl2(l), HClO, and ClO- dominate the removal of BPA at temperatures ranging from 15 to 60 °C. Besides, free radicals, including •OH and Cl2 •-, contribute minimally to BPA removal at 60 °C. Based on the elementary kinetic models, the production rate constant of Cl2(l) (32.5 M-1 s-1) is much higher than HClO (6.5 × 10-4 M-1 s-1), and its degradation rate with BPA (2 × 107 M-1 s-1) is also much faster than HClO (18 M-1 s-1). Furthermore, the degradation of BPA by Cl2(l) and HClO were enlarged by 10- and 18-fold at 60 °C compared to room temperature, suggesting waste heat utilization can enhance treatment performance. Overall, this research provides valuable insights into the effectiveness of direct PMS introduction for removing organic micropollutants from high Cl- wastewater. It further underscores the critical kinetics and mechanisms within the PMS/Cl⁻ system, presenting a cost-effective and environmentally sustainable alternative for wastewater treatment.

CuO-ZIF-8 modified electrode surface as a new electrochemical sensing platform for detection of free chlorine in aqueous solution.

This work has applied metal-organic frameworks (MOFs) with high adsorbability and catalytic activity to develop electrochemical sensors to determine free chlorine (free-Cl) concentrations in aqueous media. A zeolitic imidazolate frameworks, Zn(Hmim)2 (ZIF-8) has been synthesized and incorporated with CuO nanosheets to decorate a glassy carbon electrode (GCE) and provide a new sensor for free-Cl determination. The as-prepared ZIF-8 and CuO-ZIF-8 composites have been characterized by FESEM, EDX, XRD, and FT-IR analyses. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) utilized to characterize the CuO-ZIF-8/GC modified electrode electrochemically, demonstrated the ability of the sensor to measure free-Cl concentration. Using differential pulse voltammetry (DPV) and under the optimal conditions, the prepared CuO-ZIF-8/GC modified electrode showed a linear response in the 0.25-60 ppm range with a 12 ppb detection limit (LOD) for free-Cl concentration. Finally, the fabricated sensor was applied to analyze free-Cl from actual swimming pool water samples with promising 97.5 to 103.0% recoveries.

Association between chlorine-treated drinking water, the gut microbiome, and enteric pathogen burden in young children in Haiti: An observational study.

OBJECTIVE: The effects of sanitation and hygiene interventions on the gut microbiome and enteric pathogen burden are not well understood. We measured the association between free chlorine residue (FCR) levels in drinking water, microbiome composition, and stool enteric pathogens in infants and young children in Haiti. METHODS: FCR levels were measured in household drinking water and enteric pathogen burden was evaluated using multiplex RT-PCR of stool among 131 children from one month to five years of age living in Mirebalais, Haiti. Microbiome profiling was performed using metagenomic sequencing. RESULTS: Most individuals lived in households with undetectable FCR measured in the drinking water (112/131, 86%). Detection of enteric pathogen DNA in stool was common and did not correlate with household water FCR. The infant microbiome in households with detectable FCR demonstrated reduced richness (fewer total number of species, P = 0.04 Kruskall-Wallis test) and less diversity by Inverse Simpson measures (P = 0.05) than households with undetectable FCR. Infants in households with a detectable FCR were more likely to have abundant Bifidobacterium. Using in vitro susceptibility testing, we found that some Bifidobacterium species were resistant to chlorine. CONCLUSIONS: FCR in household drinking water did not correlate with enteric pathogen burden in our study.

Waste DVD polycarbonate substrate for screen-printed carbon electrode modified with PVP-stabilized AuNPs for continuous free chlorine detection.

An electrochemical free chlorine sensor was developed by modifying a lab-made screen-printed carbon electrode (SPCE) with gold nanoparticles synthesized with polyvinylpyrrolidone (AuNPs-PVP). The electrode was made by screen printing carbon ink on a waste digital versatile disc (SPC-wDVD). PVP was used to stabilize AuNPs. Scanning electron microscopy showed that AuNPs aggregated without the stabilizer. The electrochemical behavior of the SPC-wDVD was evaluated by comparison with commercial SPCEs from two companies. Electrochemical characterization involved cyclic voltammetry and electrochemical impedance spectroscopy. The detection of free chlorine in water samples was continuous, facilitated by a flow-injection system. In the best condition, the developed sensor exhibited linearity from 0.25 to 3.0 and 3.0 to 500 mg L-1. The limit of detection was 0.1 mg L-1. The stability of the sensor enabled the detection of free chlorine at least 475 times with an RSD of 3.2 %. The AuNPs-PVP/SPC-wDVD was able to detect free chlorine in drinking water, tap water and swimming pool water. The agreement between the results obtained with the proposed method and the standard spectrophotometric method confirmed the precision of the developed sensor.

Linear Mixed Model of Virus Disinfection by Free Chlorine to Harmonize Data Collected across Broad Environmental Conditions.

Despite the critical importance of virus disinfection by chlorine, our fundamental understanding of the relative susceptibility of different viruses to chlorine and robust quantitative relationships between virus disinfection rate constants and environmental parameters remains limited. We conducted a systematic review of virus inactivation by free chlorine and used the resulting data set to develop a linear mixed model that estimates chlorine inactivation rate constants for viruses based on experimental conditions. 570 data points were collected in our systematic review, representing 82 viruses over a broad range of environmental conditions. The harmonized inactivation rate constants under reference conditions (pH = 7.53, T = 20 °C, [Cl-] < 50 mM) spanned 5 orders of magnitude, ranging from 0.0196 to 1150 L mg-1 min-1, and uncovered important trends between viruses. Whereas common surrogate bacteriophage MS2 does not serve as a conservative chlorine disinfection surrogate for many human viruses, CVB5 was one of the most resistant viruses in the data set. The model quantifies the role of pH, temperature, and chloride levels across viruses, and an online tool allows users to estimate rate constants for viruses and conditions of interest. Results from the model identified potential shortcomings in current U.S. EPA drinking water disinfection requirements.

Degradation of organic pollutants by the Cl-/PMS process.

The viewpoints on whether high concentrations of chloride ion (Cl-) promote or inhibit the oxidation activity of activated persulfates are still inconclusive. Furthermore, the degradation of organic pollutants by the persulfates in the presence of high Cl- concentrations without any activation medium has not yet been studied. In this work, the efficiency and mechanism of degradation of organic pollutants such as carbamazepine (CBZ), sulfadiazine (SDZ), and phenol (PN) by Cl--activated PMS (denoted as Cl-/PMS) were investigated. Results showed that Cl- could effectively activate PMS for the complete removal of CBZ, SDZ, and PN with reaction kinetic constants of 0.4516 min-1, 0.01753 min-1, and 0.06805 min-1, respectively. Parameters such as PMS dose, Cl- concentration, solution pH, and initial concentrations of organic pollutants that affect the degradation efficiencies of the Cl-/PMS process were optimized. Unlike conventional activated persulfates, it was confirmed that the free chlorine was the main active species in the Cl-/PMS process. Finally, the degradation by-products of CBZ and SDZ as well as their toxicity were detected, and a possible degradation pathway for CBZ and SDZ was proposed. Though higher toxic chlorinated by-products were generated, the Cl-/PMS process was still an efficient oxidation method for the removal of organic pollutants in aqueous solutions which contain high concentrations of Cl-.

Reconsider the burn: The transient effect of a chlorine burn on controlling opportunistic pathogens in a full-scale chloraminated engineered water system.

Nitrification is a serious water-quality issue in chloraminated engineered water systems (EWSs). Nitrification is often remediated by a chlorine burn (i.e., a free­chlorine conversion), a short-term switch from chloramination to chlorination in EWSs. Opportunistic pathogens (OPs) are the dominant infectious agents in EWSs. However, the responses of OPs to a chlorine burn are unknown. This study for the first time assessed how a chlorine burn affected OPs in a full-scale EWS. We determined the impact of a 1.5-month chlorine burn on four dominant OPs (Legionella, Mycobacterium, Pseudomonas, and Vermamoeba vermiformis) in a representative full-scale chloraminated EWS in the United States. Legionella and Mycobacterium were the most abundant OPs. In the water main, the summed concentration of the four OPs during the chlorine burn [3.27 ± 1.58 log10(GCN·L-1); GCN: genome or gene copy number] was lower (p ≤ 0.001) than before the burn [4.83 ± 0.50 log10(GCN·L-1)]. After the burn, the summed concentration increased to 4.27 ± 0.68 log10(GCN·L-1), comparable to before the burn (p > 0.05), indicating a transient effect of the chlorine burn in the water main. At the residential sites, the summed concentrations of the four OPs were comparable (p > 0.05) at 5.50 ± 0.84, 5.27 ± 1.44, and 5.08 ± 0.71 log10(GCN·L-1) before, during, and after the chlorine burn, respectively. Therefore, the chlorine burn was less effective in suppressing OP (re)growth in the premise plumbing. The low effectiveness might be due to more significant water stagnation and disinfectant residual decay in the premise plumbing. Indeed, for the entire sampling period, the total chlorine residual concentration in the premise plumbing (1.8 mg Cl2·L-1) was lower than in the water main (2.4 mg Cl2·L-1). Consequently, for the entire sampling period, the summed concentration of the four OPs in the premise plumbing [5.26 ± 1.08 log10(GCN·L-1)] was significantly higher (p < 0.001) than in the water main [4.04 ± 1.25 log10(GCN·L-1)]. In addition, the chlorine burn substantially increased the levels of disinfection by-products (DBPs) in the water main. Altogether, a chlorine burn is transient or even ineffective in suppressing OP (re)growth but raises DBP concentrations in chloraminated EWSs. Therefore, the practice of chlorine burns to control nitrification should be optimized, reconsidered, or even replaced.

Different electrolytic treatments for food sanitation and conservation simulating a wash process at the packinghouse.

Microorganisms are predominantly responsible for food deterioration, necessitating the sanitization and removal of these entities from food surfaces. The packinghouse employs free chlorine in the sanitization process; however, free chlorine's propensity to react with organic matter, forming potentially toxic compounds, has led to its restriction or outright prohibition in several European countries. Therefore, this study aims to assess various washing methods, emulating packinghouse conditions, utilizing diverse forms of electrolyzed water to impede microbial proliferation and significantly enhance the food's shelf life. The subject of investigation was cherry tomatoes. The findings revealed that electrolyzed water containing NaCl exhibited superior efficacy compared to electrolysis with Na2SO4. Both forms of electrolyzed water demonstrated noteworthy effectiveness in inhibiting microorganisms, resulting in a reduction of 2.0 Log CFU mL-1 for bacteria and 1.5 Log CFU mL-1 for fungi. The electrolyzed water also exhibited a comparable capability to free chlorine in removing fecal coliforms from the tomato surfaces. Notably, both electrolyzed water treatments extended the shelf life of cherry tomatoes by at least three days, accompanied by minimal or negligible residues of free chlorine. Consequently, the electrolyzed water formulations proposed in this study present themselves as promising alternatives to traditional packinghouse sanitizers. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-023-05882-1.

Applying microelectrodes to investigate aged ductile iron and copper coupon reactivity during free chlorine application.

In drinking water distribution systems, including premise plumbing, dissolved oxygen (DO) and free chlorine (FC) are common oxidants and ductile iron (DI) and copper (Cu) are commonly used pipe materials. Microelectrodes as a tool have been applied in previous corrosion research and were used in this study to collect quantifiable data and understand DO and FC reactivity and pH changes at the water-metal interface. Using microelectrodes, pH, DO, and FC profiles from the bulk water to near and at the surface of aged DI (154-190 d) and Cu (2 d and 86-156 d) coupons were investigated during periods of flow and stagnation (30 min). Using the measured microelectrode profiles, oxidant fluxes and apparent surface reaction rate constants were calculated to elucidate differences between DO and FC reactivity with the coupons. Microelectrodes were successfully applied to measure pH, DO, and FC profiles from the bulk water to near aged DI and Cu coupon surfaces; Cu coupons aged quickly and exhibited less reactivity at 2 d with DO and FC than aged DI coupons did after 154-190 d; and for the aged DI coupon experiments, orthophosphate presence stabilized pH profiles where without orthophosphate pH fluctuations of greater than 2 pH units occurred from the bulk water to the DI coupon surface.

Nitrate electro-bioremediation and water disinfection for rural areas.

Nitrate-contaminated groundwater is a pressing issue in rural areas, where up to 40 % of the population lacks access to safely managed drinking water services. The high costs and complexity of centralised treatment in these regions exacerbate this problem. To address this challenge, the present study proposes electro-bioremediation as a more accessible decentralised alternative. Specifically, the main focus of this study is developing and evaluating a compact reactor designed to accomplish simultaneous nitrate removal and groundwater disinfection. Significantly, this study has established a new benchmark for nitrate reduction rate within bioelectrochemical reactors, achieving the maximum reported rate of 5.0 ± 0.3 kg NO3- m-3NCC d-1 at an HRTcat of 0.7 h. Furthermore, thein-situ generation of free chlorine was effective for water disinfection, resulting in a residual concentration of up to 4.4 ± 1.1 mg Cl2 L-1 in the effluent at the same HRTcat of 0.7 h. These achievements enabled the treated water to meet the drinking water standards for nitrogen compounds (nitrate, nitrite, and nitrous oxide) as well as pathogens content (T. coliforms, E. coli, and Enterococcus). In conclusion, this study demonstrates the potential of the electro-bioremediation of nitrate-contaminated groundwater as a decentralised water treatment system in rural areas with a competitive operational cost of 1.05 ± 0.16 € m-3.

Toward the autonomous flushing of building plumbing: Characterizing oxidation-reduction potential and temperature sensor dynamics.

Manual flushing of building plumbing is commonly used to address water quality issues that arise from water stagnation. Autonomous flushing informed by sensors has the potential to aid in the management of building plumbing, but a number of knowledge gaps hinder its application. This study evaluates autonomous flushing of building plumbing with online sensor and actuator nodes deployed under kitchen sinks in five residential houses. Online oxidation-reduction potential (ORP) and temperature data were collected for nine weeks during the winter and summer in houses with both free chlorine and chloramine. ORP levels in houses with free chlorine residuals decreased after overnight stagnation. The overnight decrease in ORP was not observed when tap water was automatically flushed for five minutes at 6:00 h every morning. ORP levels in houses with chloramine residuals did not decrease consistently after overnight stagnation, and daily automated flushes did not have an observable effect on the ORP signals. Additional laboratory experiments were carried out to evaluate ORP signals during chlorine decay and after incremental changes in chlorine, as would be expected in building plumbing conditions. Results from the lab and field deployments suggest on-line ORP sensors may be used to detect free chlorine decay due to stagnating water, but are not as effective in detecting chloramine decay. However, field results also suggest ORP may not respond as expected on a timely manner after free chlorine or chloramine have been restored, hindering their applicability in developing control algorithms. In this paper we tested twice-daily five-minute automatic flushing and found that it counteracts water quality degradation associated with overnight stagnation in free chlorine systems. An automatic sensor-based flushing is proposed using online temperature sensor data to determine when flushing has reached water from the main. The results suggest that flushing informed by temperature sensors can reduce the flushing time by 46 % compared to the preset five-minute static flush.

Cobalt-based metal-organic framework-functionalized graphene oxide modified electrode as a new electrochemical sensing platform for detection of free chlorine in aqueous solution.

This work reports the profit of using a MOF compound for developing a sensitive electrochemical sensor to free chlorine detection in an aqueous solution. Co-MOF and FGO composites were synthesized and combined with the carbon paste (CP) to prepare an efficient electrochemical sensor with high sensing ability. The fabricated Co-MOF and FGO composites were characterized by SEM, EDX, FT-IR, and XRD techniques. Meanwhile, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to assess the electrochemical performance of the Co-MOF-FGO/CP modified electrode. Under the optimized condition, the amperometric detection showed that the reduction current of free chlorine increased linearly with a coefficient determination of 0.995 during its wide concentration range of 0.1-700 ppm. Also the detection limit (LOD) (S/N = 3) was 0.01 ppm. The selectivity of the sensor was tested with possible interferences, and satisfactory results were obtained. The proposed sensor was successfully used to determine the free chlorine in tap water and swimming pool water real samples. The results suggested that this proposed sensor could pave the way for developing the electrochemical sensor of free chlorine in aqueous media with MOFs.

Modeling the Chlorine Series from the Treatment Plant of Drinking Water in Constanta, Romania.

Ensuring good drinking water quality, which does not damage the population's health, should be a priority of decision factors. Therefore, water treatment must be carried out to remove the contaminants. Chlorination is one of the most used treatment procedures. Modeling the free chlorine residual concentration series in the water distribution network provides the water supply managers with a tool for predicting residual chlorine concentration in the networks. With regard to this idea, this article proposes alternative models for the monthly free chlorine residual concentration series collected at the Palas Constanta Water Treatment Plant, in Romania, from January 2013 to December 2018. The forecasts based on the determined models are provided, and the best results are highlighted.

Microelectrode evaluation of in situ oxidant reactivity and pH variability at new ductile iron and copper coupon surfaces.

Thirty-two short term (∼7.5 h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9), dissolved inorganic carbon (DIC, 10 or 50 mg C L-1) and phosphate (0 or 3 mg P L-1) concentrations and 4 mg Cl2 L-1 free chlorine or monochloramine. To quantify oxidant reactivity with the new metal coupons, microelectrodes were used to obtain oxidant (free chlorine or monochloramine and dissolved oxygen (DO)) concentration and pH microprofiles from the bulk water to near the metal coupon surface. From the microprofiles, apparent surface reaction rate constants (k) were determined for each oxidant. An ANOVA analysis evaluated if the five variables (Material, Oxidant, Phosphate, DIC, and pH) significantly affected estimates of k, finding that the Material and Oxidant variables and their interaction were statistically significant (p<0.05), but the effect of variables of Phosphate, DIC, and pH on k values were not significant in this study. In general, both ductile iron and copper coupons showed significant surface reactivity towards free chlorine and monochloramine. For ductile iron, DO consumption was greater than for copper, which showed minimal DO reactivity, and DO was less reactive towards the copper surface than either free chlorine or monochloramine. Furthermore, pH microprofiles provided insight into the complexity that might exist near corroding metal surfaces where the bulk water pH may be substantially different from that measured near metal surfaces which is significant as pH is a controlling variable in terms of scale formation and metal solubility. This study represents an important first step towards using microelectrodes to (1) understand and provide direct measurement of oxidant microprofiles from the bulk water to the metal surface; (2) determine pipe wall reactivity using the directly measured concentrations profiles versus estimated pipe wall reactivity from bulk water measurements, and (3) understand how variables measured by bulk water samples (e.g., pH) may be drastically different from what is occurring at and near the metal surface. Together, these insights will assist in understanding disinfectant residual maintenance, corrosion, and metal release.

Inactivation of SARS-CoV-2 in Water by Chlorination.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is present in both respiratory secretions and feces, creating its potential for transmission by swimming pools. Recreational water activity is known to be at increased risk of respiratory infections and respiratory viruses have caused been detected and have caused outbreaks in swimming pools. However, little is known regarding the chlorine inactivation of SARS-CoV-2 in water typical of swimming pools in the USA. In this study, the inactivation of SARS-CoV-2 Isolate hCoV-19/USA-WA1/2020 was observed in water by chlorination. All experiments were conducted within a BSL-3 laboratory at room temperature. Our results show that the virus was reduced by 3.5 log (> 99.9%) after 30 s of 2.05-mg/L free chlorine contact and greater than 4.17 log (limit of detection) (> 99.99%) within 2 min.

Photochemical Transformation of Free Chlorine Induced by Triplet State Dissolved Organic Matter.

Photolysis of free chlorine is an increasingly recognized approach for effectively inactivating microorganisms and eliminating trace organic contaminants. However, the impact of dissolved organic matter (DOM), which is ubiquitous in engineered water systems, on free chlorine photolysis is not yet well understood. In this study, triplet state DOM (3DOM*) was found to cause the decay of free chlorine for the first time. By using laser flash photolysis, the scavenging rate constants of triplet state model photosensitizers by free chlorine at pH 7.0 were determined to be in the range of (0.26-3.33) × 109 M-1 s-1. 3DOM*, acting as a reductant, reacted with free chlorine at an estimated reaction rate constant of 1.22(±0.22) × 109 M-1 s-1 at pH 7.0. This study revealed an overlooked pathway of free chlorine decay during UV irradiation in the presence of DOM. Besides the DOM's light screening ability and scavenging of radicals or free chlorine, 3DOM* played an important role in the decay of free chlorine. This reaction pathway accounted for a significant proportion of the decay of free chlorine, ranging from 23 to 45%, even when DOM concentrations were below 3 mgC L-1 and a free chlorine dose of 70 µM was present during UV irradiation at 254 nm. The generation of HO• and Cl• from the oxidation of 3DOM* by free chlorine was confirmed by electron paramagnetic resonance and quantified by chemical probes. By inputting the newly observed pathway in the kinetics model, the decay of free chlorine in UV254-irradiated DOM solution can be well predicted.

Kinetics study of chloride-activated peracetic acid for purifying bisphenol A: Role of Cl2/HClO and carbon-centered radicals.

Peracetic acid is an emerging oxidant and disinfectant for wastewater purification. In this study, we first developed a comprehensive and accurate model to elucidate the reaction mechanisms and simulate reaction kinetics of peracetic acid (PAA, CH3C(=O)OOH) activated by chloride (Cl-) based on experimental results and literature. A diversity of experiments methods (e.g., quenching experiments, probe compounds degradation, electron paramagnetic resonance (EPR) measurements) and kinetic modeling were used to determine the reactive species. As a result, carbon-centered radicals and free chlorine reactive species (Cl2 and HClO) were devoted to BPA degradation in the PAA/Cl- system. The carbon-centered radicals CH3C(=O)OO•, CH3C(=O)O•, CH3OO•, and •CH3 greatly accelerated BPA degradation with their corresponding kinetics of kCH3C(=O)OO•, BPA = 2 × 108 M-1 s-1, kCH3C(=O)O•, BPA = 2 × 107 M-1 s-1, k•CH3, BPA = 2 × 106 M-1 s-1 and kCH3OO•, BPA = 2 × 104 M-1 s-1. Dissolved Cl2(l) species was also important for BPA degradation with kCl2, BPA of 2 × 107 M-1 s-1, much higher than HClO/ClO- of kHClO, BPA = 1.2 × 101 M-1 s-1 and kClO-, BPA = 9 × 10-3 M-1 s-1. While free chlorine tends to transform BPA to estrogenic chlorinated organic products, the primary degradation of BPA by carbon-centered radicals results in chlorine-free products, reducing the production of disinfection byproducts during the treatment of saline wastewater. This study improves the knowledge of reaction kinetics and mechanism and reactive species generation in the PAA/Cl- system.

Predicting heterotrophic plate count exceedance in tap water: A binary classification model supervised by culture-independent data.

Culture-independent data can be utilized to identify heterotrophic plate count (HPC) exceedances in drinking water. Although HPC represents less than 1% of the bacterial community and exhibits time lags of several days, HPC data are widely used to assess the microbiological quality of drinking water and are incorporated into drinking water standards. The present study confirmed the nonlinear relationships between HPC, intact cell count (ICC), and adenosine triphosphate (ATP) in tap water samples (stagnant and flushed). By using a combination of ICC, ATP, and free chlorine data as inputs, we show that HPC exceedance can be classified using a 2-layer feed-forward artificial neural network (ANN). Despite the nonlinearity of HPC, the best binary classification model showed accuracies of 95%, sensitivity of 91%, and specificity of 96%. ICC and chlorine concentrations were the most important features for classifiers. The main limitations, such as sample size and class imbalance, were also discussed. The present model provides the ability to convert data from emerging measurement techniques into established and well-understood measures, overcoming culture dependence and offering near real-time data to help ensure the biostability and safety of drinking water.

From black water to flushing water: potential applications of chlorine-mediated indirect electrooxidation for ammonia removal.

Removing ammonia from black water is one of the most urgent issues before it can be recycled as flushing water. In this study, an electrochemical oxidation (EO) process with commercial Ti/IrO2-RuO2 anodes to treat black water could remove 100% of different concentrations of ammonia by adjusting the dosage of chloride. Through the relationship between ammonia, chloride, and corresponding the pseudo-first-order degradation rate constant (Kobs), we could determine the chloride dosage and predict the kinetics of ammonia oxidation based on initial ammonia concentration in black water. The optimal N/Cl molar ratio was 1:1.8. The difference between black water and the model solution in terms of ammonia removal efficiency and oxidation products was explored. A higher chloride dosage was beneficial for removing ammonia and shortening the treatment cycle, but it also led to the generation of toxic by-products. Especially HClO and ClO3- generated in black water were 1.2 and 1.5 times more than the synthesized model solution under 40 mA cm-2. Through SEM characterization of electrodes and repeated experiments, the electrodes always maintained a high treatment efficiency. These results demonstrated the potential of the electrochemical process as a treatment method for black water.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review.

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH2Cl- and ClO2-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.