Chlorine Dose Research Articles

Optimization of Breakpoint Chlorination Technologies for Drinking Water Treatment: a Hungarian Case Study

Ammonium ion is one of the major pollutants found in drinking water sources in Hungary, especially in deep aquifers. under oxidative conditions, ammonium can transform into nitrite ions in the water system, posing potential health risks. In Hungary mostly biological process or breakpoint chlorination are used to eliminate ammonium ion from raw water during the drinking water treatment process. When breakpoint chlorination is applied, harmful by-products are formed. Trihalomethanes concentrations have long been regulated in Hungary, therefore during the design and optimization of the breakpoint technologies trihalomethane concentrations have been considered. However, haloacetic acids (HAA5) and chlorate ion have been recently regulated in accordance with EU Directive 2020/2184. Chlorate is a by-product that appears in treated water when sodium hypochlorite is used in breakpoint chlorination.Experiments were carried out at four Hungarian case study areas to determine the optimal strategy for breakpoint chlorination: applying higher chlorine dosages with lower contact times, or lower chlorine dosages with higher contact times. The investigations concluded that the preferable dosing strategy is to use lower chlorine concentrations and longer contact times. This approach reduces chemical demand (cost-effective) and has a neutral effect on THMs formation. it can be concluded that when the raw water contains ammonium ion concentrations above 0.5 mg/l, the use of sodium hypochlorite may raise concerns due to elevated chlorate ion levels in the treated water, particularly during summer. Further research is required to expand the optimization strategy, considering not only ammonium and trihalomethane concentrations but also chlorate concentrations.

Variation in organic matter characteristics and mitigation of ultrafiltration membrane fouling by chlorine and UV/chlorine pre-oxidation in secondary effluent treatment

Membrane fouling caused by effluent organic matter (EfOM) limits its further application in wastewater reuse. In this study, the effect of UV/chlorine pretreatment on membrane fouling was investigated in treating secondary effluent by ultrafiltration (UF) process. The relation between organic matter changes and fouling alleviation after UV/chlorine pretreatment was also studied according to the molecular weight (MW) changes in various resin fractions derived from EfOM. Results showed that UV/chlorine pretreatment effectively alleviated irreversible fouling, whereas chlorine pre-oxidation primarily mitigated reversible fouling. UV/chlorine pre-oxidation reduced 18% of reversible membrane fouling and 38% of irreversible membrane fouling at a chlorine dosage of 8 mg/L, indicating better performance in membrane fouling mitigation than chlorine pre-oxidation. UV/chlorine pre-oxidation also decreased dissolved organic matter in the UF permeate. The hydrophobic acidic (HPO-A) fraction caused dominant membrane fouling, while the hydrophilic (HPI) fraction contained most of high MW organic matter. Pre-oxidation changed the polarity of organic matter in the HPO-A fraction and decomposed the organics of high MW in the HPI fraction, which alleviated membrane fouling. These results showed that UV/chlorine pre-oxidation was a prospective pretreatment process prior to UF in wastewater reclamation.

Effect of low doses of active chlorine on commensal populations of intestinal bacteria in rats by oral ingestion

Chlorine-containing substances are widely used as disinfectants for treating equipment surfaces and technological aids for antimicrobial treatment of a number of foodstuff in the food industry. The toxic and bactericidal effects of the active (free) chlorine they contain are well understood for the concentrations used in practice, whereas little is known about the effect of its residual (subinhibitory) amounts on the organism and on the microbiota, including the ability to induce antimicrobial resistance. The aim of the study was to investigate the effect of different doses of active chlorine at oral administration on the commensal bacteria of intestinal microbiota, body weight gain and micromorphological features of the liver in rats. Material and methods. The study was carried out on male Wistar rats, with an initial body weight of 90-100 g, which for 4 weeks received doses of active chlorine together with drinking water ad libitum, with the given concentration: subinhibitory (10 mg/L), threshold (50 mg/L) and aggravated (100 mg/L). Chloramine was used as a chlorinecontaining agent stable in aqueous solution. Body weight gain was monitored daily. After decapitation, the caecum was taken for microbiota examination as well as the liver. The phenotypic antimicrobial resistance characteristics of Enterobacteriaceae and Enterococci were studied by the disk diffusion method. Additionally, a micromorphologic study of liver slices was performed. Results. Insignificant negative deviations in the body weight gain of rats in the experimental groups receiving subinhibitory doses of active chlorine, combined with a reduced level of Enterococci and Enterobacteriaceae representatives, were revealed. No significant effect of chlorine on the levels of resistant Escherichia coli populations was found, but a tendency to exhibit antimicrobial resistance of Enterococci isolated from rats receiving low doses of active chlorine (10 and 50 mg/l) was detected. No signs of toxic effect on the liver tissue most sensitive to chlorine were detected, but some accumulations of inflammatory cells in the liver slice were revealed. Conclusion. Low doses of chlorine-containing substances at their oral consumption are not indifferent for rats' organism, causing negative phenomena in intestinal bacteria and in liver tissues at the level of tendency. It is expedient to continue studies in this direction.

Predicting the concentration of brominated trihalomethanes in drinking water

The paper presents a method for predicting the content of brominated trihalogen methanes in drinking water depending on turbidity, chromaticity, oxidizability of water source water and chlorine dose. It was found that the mathematical approach associated with the shift of time series of water quality indicators is appropriate to use only for describing the content of bromodichloromethane depending on water quality indicators (turbidity, color and oxidizability). The introduction of chlorine dose as an independent variable into the multiple regression equation does not improve the quality of the model.

Laboratory tests of the stability of disinfectants for different quality of water

The last water treatment process is disinfection and it has two purposes. The main purpose of disinfection is to kill or inactivate pathogens. A secondary purpose is to provide a residual disinfectant concentration in drinking water and to prevent microbial growth in water distribution systems. Although most pathogens (99 to 99.9%) are removed by coagulation, flocculation, sedimentation, and filtration, disinfection is a critical process for protecting the public from waterborne infections. Common disinfectants include chlorine gas, sodium hypochlorite, chloramines, chlorine dioxide, ozone and ultraviolet radiation. Each disinfection method has its advantages and disadvantages. Among the disadvantages of using sodium hypochlorite, in addition to the formation of disinfection by-products, the stability of the used agent is also important. Laboratory tests of the stability of disinfectants were carried out in drinking water of different quality depending on the pH value, water temperature and total water mineralization at different contact time in water (from 0 to 48 hours). To monitor the stability of disinfectants, chlorine-based disinfectants were selected, namely sodium hypochlorite prepared in the classic way and by electrolysis of brine. The stability of these disinfectants was verified in low-mineralized surface water from the Turček water reservoir, medium mineralized groundwater from the Sihot’ water source and groundwater from a private well in village of Ol’dza with highly mineralized water. Active chlorine doses in the range of 0.28-0.35 mg/L were used to verify the stability of sodium hypochlorite prepared in the classic way in selected drinking waters. When verifying the stability of sodium hypochlorite prepared by electrolysis of brine, doses of active chlorine in the range of 0.25-0.30 mg/L were applied. When verifying the stability of sodium hypochlorite produced by two different methods (chemical process, brine electrolysis), the dependence of the increasing stability of these disinfectants with a decrease in pH value and water temperature was demonstrated. The dependence of chlorine stability is significantly influenced by the water temperature, less so by the pH value of the water. Reaction kinetics of 0th, 1st and 2nd order was studied for better understanding of this process.

Disinfection as a stabilization method for backwash water reuse

The necessity to limit water use and for using recirculating economy leads to much attention being devoted to the reuse of backwash from filter flushing in water treatment plants. Pre-treatment of backwash water, especially the elimination of harmful substances and microorganisms, is necessary for its reuse. This paper presents an evaluation of the possibility of achieving water backwash biostability from surface and infiltration water treatment plants by subjecting it to chlorination or irradiation with UV light. The results of this study have shown that it is necessary to use large chlorine and radiation doses, irrespective of the type of treated water. At the same time, the optimal disinfection process parameters were determined, which ensured an elimination of pathogenic microorganisms, and limiting the number of other microorganisms. Both analyzed disinfection methods allow for the recirculation of backwash water into the beginning of the water treatment process, yet physical disinfection requires larger investments and operating costs. The increased cost in treating backwash water with UV as compared to chlorine is small, yet it eliminates the problem of the creation of disinfection by-products, whose concentration were significant, but did not exceed the values allowed for drinking water. The disinfection of backwash water from treating surface and infiltration water allowed for a reduction in sourced water in the amount of about 4% of treated water volume.

Suların Klorla Dezenfeksiyonunda Trihalometan Oluşumuna Hümik Asit ve Bromürün Etkisi

Chlorination is one of the most important methods used in water disinfection. Chlorine reacts with natural organic substances in water and causes the formation of disinfection byproducts that might cause health problems. The predominant by-product of chlorination is trihalomethanes. Humic substances, which make up the majority of natural organic substances, are the primary precursors of trihalomethanes. In this study, the effect of different doses of chlorine on the formation of chloroform, bromodichloromethane, dibromochloromethane and bromoform in the presence of natural organic matter and bromide in drinking water was evaluated. Artificial raw water samples prepared with the addition of 2, 3 and 5 mg/L humic acid representing natural organic matter were subjected to chlorination at doses of 1, 2 and 3 mg/L and analysed on the 0th, 3rd and 7th day. The only trihalomethane formed was chloroform with a concentration of 20.52-131.13 μg/L. Increased humic acid and chlorine levels resulted in increased chloroform content. Free chlorine in the water caused chloroform formation to continue even on the 7th day. Accordingly, the amount of chloroform formed increased with the contact time. While the chlorine dose was constant, increased humic acid resulted in decreased free chlorine. To evaluate the effect of bromide on trihalomethane formation, 200 μg/L bromide was added to 2 mg/L humic acid containing water, and 1 mg/L and 2 mg/L chlorination was applied. At the end of the chlorination process in bromide-free waters, only 23.46-41.90 μg/L of chloroform was formed. In the presence of bromide, chloroform, bromodichloromethane, dibromochloromethane and bromoform were formed and the total trihalomethane level increased to 50.03-85.59 μg/L. While the ratio of brominated trihalomethane increased, the amount of chlorinated species decreased.

Comparative effectiveness of sequential and synergistic (VUV/)UV and chlorine disinfection on DBPs and humic acid reduction

The widespread use of chlorine during disinfection has led to the problems of disinfection by-products (DBPs). Recently, the combination of ultraviolet (UV, 254 nm) and vacuum ultraviolet (VUV, 185 nm) with chlorine has been considered a promising strategy to mitigate the formation of DBPs. This study systematically evaluated the efficacy of six different disinfection methods in abating humic acid (HA), a common precursor of DBPs (UV-Chlorine, VUV/UV-Chlorine, Chlorine-UV, Chlorine-VUV/UV, UV/Chlorine, and VUV/UV/Chlorine). Under 40 mJ/cm2 UV fluence and 3 mg/L chlorine dose, the synergistic processes yielded DBP levels below 20 μg/L, whereas sequential disinfection resulted in DBP levels exceeding 100 μg/L. Additionally, there was no significant difference in the formation of DBPs between the two methods of chlorination followed by irradiation. However, for irradiation followed by chlorination, the addition of VUV led to an increase of 50 μg/L in trihalomethanes (THMs). As the irradiation time increased, the inclusion of VUV demonstrated enhanced control of DBP levels in the sequential disinfection process. Moreover, compared to UV/Chlorine, at 13 mg/L chlorine dose in VUV/UV/Chlorine process, the inclusion of VUV expedited the appearance of peak DBPs by two minutes and reduced the peak value by 25.6 %, but the DBP yield was 12.9 times higher than that at a chlorine dose of 3 mg/L. This study, comparing six combination disinfection methods, will provide deeper insights into precursor abatement and DBP control during drinking water disinfection.

Synergistic Use of Thermostable Laccase and Xylanase in Optimizing the Pre-Bleaching of Kraft Pulp

The continuous requirement for pre-bleaching processes on kraft pulp, employing a range of compatible enzymes, aims to mitigate the pollution caused by chemical bleaching agents. In the present study, the laccase-producing bacterium Bacillus licheniformis BK-1 was isolated from the Bakreshwar hot spring in India and tested for laccase production using different lignocellulosic substrates. The isolate was found to produce maximum laccase (8.25 IU/mL) in the presence of rice bran as a substrate, followed by 5.14 IU/mL using sawdust over a 48 h period. Laccase production doubled when medium parameters were optimized using a central composite design. The bleaching of rice straw pulp was accomplished using a laccase, xylanase (previously extracted from the same bacteria), and laccase–xylanase mixture. The mix-wood kraft pulp treated with the enzyme mixture at pH 7.0 and 50 °C temperature for up to 180 min reduced the chlorine amount by 50% compared to the control. The results also revealed that the enzyme mixture improved the pulp’s optical (brightness 10.39%) and physical (tear index 39.77%, burst index 22.82%, and tensile strength 14.28%) properties with 50% chlorine dose. These exceptional properties underscore the enzyme mixture’s suitability for pulp pre-bleaching in paper manufacturing, offering a safer and more environmentally friendly process.

Effect of preoxidation on fouling mitigation in a low-pressure membrane system with clean-in-place (CIP) treatment

The study investigates the impact of biological (soluble microbial products), organic (humic acid), and inorganic foulants (Al, Mn, and Fe) on the structure of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes during filtration processes. While different forms of Al, including mononuclear (Ala), colloidal (Alc), and polymeric (Alb) species, were also analyzed and a chlorination dose of 1.5 mg.L−1 was used as pretreatment for the feed water. The results revealed that the PES membranes exposed to the untreated feed solution were more vulnerable to severe structural deterioration as compared to PVDF membranes, in the presence of organic/biological foulants and complex mixtures of organic and inorganic foulants. Presence of carbonate (O-C=O) and carboxylic groups on PES membranes and the reduction of hydrophilic additives on PVDF membranes after exposure to the feed streams was observed. Moreover, the pore size of the PES and PVDF membranes increased to 1308.1 nm and 287.8 nm, respectively, at the end of study. The PVDF membranes exhibited severe fouling than PES membranes due to strong adsorption potential for the foulants. Moreover, Alb had stronger fouling effect that Ala and Alc, while pre-chlorination increased charge neutralization and reduced fouling due to weaker binding with the organic foulants. Results from Hermia's fouling model confirmed the occurrence of complete blocking, followed by the formation of a cake layer and intermediate fouling.

Reinforcement learning-based DSS for coagulant and disinfectant dosage selection on drinking water treatment plants

Abstract The treatments to be applied for water purification must be dynamically adaptable to the raw water conditions. Currently, treatments are applied based on standards that are not optimized for the circumstances of each drinking water treatment plant (DWTP), neither for critical events. This paper presents a methodology for the creation of an Artificial Intelligence (AI) decision support system (DSS), encompassing the principal steps of the drinking water treatment processes (coagulation, sedimentation, filtration and disinfection), based on reinforcement learning techniques, that provides suggestions about the most efficient treatments (coagulant and chlorine dosages) for various raw water conditions, including critical events such as heavy rain and saline intrusions. Together with the model, a retraining strategy is included so the DSS adapts itself to the specific circumstances of each different DWTP. The model has been developed and validated in a DWTP replica. Furthermore, the model has been provided to a real DWTP to obtain feedback from experienced staff. The results and evaluation of the model are promising as a first approach on a DSS for drinking water treatments suggestion, although future versions might require more water quality parameters to characterize the raw water.

Premise Plumbing Pipe Materials and In-Building Disinfectants Shape the Potential for Proliferation of Pathogens and Antibiotic Resistance Genes.

In-building disinfectants are commonly applied to control the growth of pathogens in plumbing, particularly in facilities such as hospitals that house vulnerable populations. However, their application has not been well optimized, especially with respect to interactive effects with pipe materials and potential unintended effects, such as enrichment of antibiotic resistance genes (ARGs) across the microbial community. Here, we used triplicate convectively mixed pipe reactors consisting of three pipe materials (PVC, copper, and iron) for replicated simulation of the distal reaches of premise plumbing and evaluated the effects of incrementally increased doses of chlorine, chloramine, chlorine dioxide, and copper-silver disinfectants. We used shotgun metagenomic sequencing to characterize the resulting succession of the corresponding microbiomes over the course of 37 weeks. We found that both disinfectants and pipe material affected ARG and microbial community taxonomic composition both independently and interactively. Water quality and total bacterial numbers were not found to be predictive of pathogenic species markers. One result of particular concern was the tendency of disinfectants, especially monochloramine, to enrich ARGs. Metagenome assembly indicated that many ARGs were enriched specifically among the pathogenic species. Functional gene analysis was indicative of a response of the microbes to oxidative stress, which is known to co/cross-select for antibiotic resistance. These findings emphasize the need for a holistic evaluation of pathogen control strategies for plumbing.

Integrated EPANET-MSX process models of chlorine and its by-products in drinking water distribution systems.

EPANET and its commercial derivatives are the most widely-used software packages for modeling free chlorine and its by-products in drinking water distribution systems. Yet, they are not sufficiently accurate, general, or efficient for deriving optimal chlorine dosing strategies at different seasonal temperatures. To overcome EPANET's limitations, an integrated set of rigorously validated multispecies process models are proposed for application within the EPANET-MSX environment. An executable (command-line) version of these MSX models is supplied for use either within the MSX environment or embedded in commercial versions of MSX. A new general method was devised to obtain output of any intermediate coefficient or variable involved in the simulation. This overcomes MSX's limited output options. When the debugged models were applied to a real distribution system, the optimal chlorine dose for summer required almost double the chlorine dose needed in winter. A lower initial dose combined with a downstream booster dose required less chlorine in total. Formal optimization techniques are needed to efficiently obtain similar strategies in more complex systems. PRACTITIONER POINTS: EPANET water quality models are not accurate or general enough for deriving optimal chlorine dosing strategies in distribution systems. Integrated EPNET-MSX models of chlorine reactions in bulk water and at pipe walls, and associated by-product formation, overcome EPANET's limitations. To verify model authenticity, a general technique was developed to obtain values of coefficients and variables within an EPANET-MSX simulation. EPANET-MSX command lines implementing these integrated EPANET-MSX models are presented with verified results for optimal initial and booster dosing strategies. Optimal summer dosing in a real system of rough pipes was almost double that required in winter.

A Study on Evaluation of Manganese Removal Efficiency by Oxidant types Based on Experimental Data

Objectives : The purpose of this study was to investigate the treatment efficiency according to the oxidant types for dissolved manganese in the inflow of raw water into the water treatment plant in Korea.Methods : Three types of oxidant were selected: chlorine, ozone, and potassium permanganate. Experimental factors influencing manganese removal efficiency were determined as dissolved manganese concentration in raw water, dose, water temperature, pH, and contact time. In addition, total experimental schemes were designed according to the design of experiments method. According to the designed analysis method, the mentioned factors were used as multi variables on which evaluate the manganese removal efficiency.Results and Discussion : When using chlorine, the effect of pH was the greatest, followed by dose, water temperature, and contact time in order to have a significant effect on removal efficiency. In the case of using ozone, the pH effect was relatively large at low concentration of dissolved manganese, and the dose effect was found to be greater as the concentration was increased. Also, when potassium permanganate was used, the effect of pH, contact time and temperature was insignificant, while the effect of dose was the greatest for manganese removal.Conclusion : The optimum dose of chlorine is about three times to secure a removal rate of about 40 to 80%. The optimum dose of ozone was 1.0 to 1.6 mg/L, and it was found that a removal rate of at least 40% or more could be secured. Also, the optimum dose of potassium permanganate is 1.7 to 2.5 times of the dissolved manganese concentration, and it is possible to secure a removal rate of at least 60%.

Release of biochar-derived dissolved organic matter and the formation of chlorination disinfection by-products: Effects of pH and chlorine dosage

Transformation, fragmentation, dissolution, and oxidation of biochar are inevitable in the environment, which will undoubtedly accelerate the release of biochar-derived dissolved organic matter (BDOM) into various water bodies. In addition, biochar may affect disinfection by-products (DBPs) during water treatment and subsequent disinfection. In this study, biochars were derived at three selected pyrolysis temperatures (350 °C, 500 °C, and 650 °C) from rice husk, wheat straw, and shrimp shell, and BDOM was extracted from biochar-derived in artificial seawater and ultrapure water. The TOC analyzer results showed that the concentrations of three BDOM decreased with increasing pyrolysis temperature. The BDOM derived from rice husk biochar and wheat straw biochar in seawater was lower than that in ultrapure water, while that of shrimp shell biochar showed an opposite trend, being released in seawater at nearly twice the extent of that in ultrapure water at 350 °C. Moreover, BDOM showed a catalytic effect on chlorination, and GC analysis showed that the concentrations of its DBPs were affected by pH. The concentration of halogenated acetic acid reached the highest value (54.51 μg/L) in weak acidic environment, while the concentrations of trihalomethane and halogenated acetonitrile had the highest values (23.63 and 47.53 μg/L, respectively) in alkaline conditions. The concentrations of all the three DBPs were lowest under neutral pH conditions. In addition, the volatile halogenated DBPs such as dichloroacetone and trichloroacetone were easily hydrolyzed under alkaline conditions. Therefore, it is something be aware of the release of BDOM and the effects of chlorination DBPs when biochar is used for water treatment or water purification.

Exploring chlorination as a removal process for antiretroviral drugs (Nevirapine and Efavirenz) from water: Effect of operational parameters, kinetics, and trihalomethane formation

This study investigates the removal of antiretroviral drugs (ARVs), Nevirapine (NVP) and Efavirenz (EFV), from drinking water through chlorination, focusing on the influence of pH, temperature, chlorine concentration, and ARV initial concentration on the degradation kinetics and trihalomethane (THM) formation. At 25 °C and an initial concentration of 100 μg/L, the degradation trends for both ARVs were examined across varying pH levels. EFV exhibited greater pH sensitivity, with removal increasing from 37 % at pH 5.5 to 68 % at pH 8, while NVP removal increased only from 40 % at pH 5.5 to 48 % at pH 8. Temperature also played an essential role, as the removal of both ARVs increased with rising temperature, indicating an endothermic reaction. Higher chlorine concentrations resulted in increased removal, >90 % at 5 mg/L for both ARVs. Kinetic analysis revealed second-order behaviour, with higher rate constants observed at pH 5.5–7 for NVP and pH 7–8 for EFV. The intrinsic chlorination rate constants for both ARVs were estimated. The calculated half-lives indicated slow removal. The study also assessed contact time for NVP and EFV in a plug-flow reactor (PFR) and continuous stirred tank reactor model (CSTR). Also considering hydraulic residence time (HRT) rather than reaction time to assess the average amount of time that the ARVs spent in the selected reactors. The HRT for a CSTR was lower than the PFR, and the estimated HRT for a CSTR was a feasible value. The minimum HRT came out to 1.56 h (pH 7.5 and a temperature of 25 °C) for NVP and 1.07 h (pH 7 and a temperature of 25 °C) for EFV. Finally, THM formation was observed, with chloroform, dibromochloromethane and bromoform detected. Among the three THMs, the most significant change occurred between 4 and 6 h, with chloroform levels increasing from 31.59 μg/L to 63.49 μg/L. This study underscores the influence of operational parameters on ARV removal via chlorination. Highlighting pH sensitivity, temperature control, precise chlorine dosage, and environmental concerns such as trihalomethane formation ensures effective disinfection while minimizing negative impacts on both water quality and the environment. Emphasizing the importance of a comprehensive approach to ARV removal in water treatment processes is a proactive measure that integrates considerations of environmental impact, public health, regulatory compliance, and long-term sustainability into the design and operation of water treatment facilities.

The Identification of Selective Pathogenic Microbial Community Biofilms in Different Distribution Pipeline Materials and Their Disinfection Kinetics

Biofilms in water distribution lines strongly affect water safety as they are the main carriers of pathogens. The current study investigated the biofilm formation and identification of selected pathogens in different distribution pipeline materials and their disinfection method in an annular reactor (AR). Initially, the quality of the flowing water from each pipeline material was analyzed, i.e., pH, TDS, EC, turbidity, and salinity; then, the biofilm formation was monitored for each material, i.e., ABS, PC, PVC, PP, and HDPE. Further, the disinfection kinetics of biofilm at different chlorine doses, i.e., 0.5, 1.0, 1.5, and 2.0 mg/L, was investigated. The selected pathogens, i.e., E. coli, Pseudomonas, Shigella, Salmonella sp., and Vibrio sp. were identified in biofilms formed in different pipeline materials. The disinfection kinetics results showed that a chlorine dose of 2.0 mg/L was the most effective in disinfecting selected pathogens. Following the disinfection kinetics, it was observed that Salmonella sp. was disinfected within 7 days, whereas other pathogenic biofilms were disinfected within 14 days. The efficacy of chlorine disinfection was affected by the types of pipeline materials. The study outcomes could provide insights into biofilms’ disinfection method and the selection of suitable pipeline materials to ensure drinking water safety.

Modeling Chlorine Decay in Reclaimed Water Distribution Systems—A Lisbon Area Case Study

Climate change has emerged as a global challenge, with consequences for the environment and societies. To mitigate its impacts, reclaimed water (RW) offers potential by reducing water withdrawal and minimizing pollution discharges in the environment. Safe RW requires disinfection and a sound management of chlorine residuals throughout the RW distribution systems (RWDSs). This study focuses on implementing and calibrating a chlorine decay model using EPANET-MSX in a real RWDS, incorporating both bulk and wall decays. The bulk decay accounts for reactions of monochloramine formation, auto-decomposition, and depletion by a parallel second-order mechanism where monochloramine reacts both with fast and slow organic matter reactive fractions. Two wall decays were considered in the RWDS, one in the tank, modeled through an overall wall decay constant, and one in the pipes, modeled through a wall decay constant. Field experiments were conducted to calibrate the complete model. This model was used as a support tool to diagnose the RWDS status condition and cleaning needs, and to manage its operation. Through simulated scenarios considering monochloramine wall decays similar to those observed in drinking water distribution systems, the model allowed predicting adequate chlorine dosing in summer and winter scenarios, so as to guarantee monochloramine concentrations between 1 mg/L and 5 mg/L through the network. These results point to the potential use of much lower doses than the ones currently applied.

Novel UV-LED-driven photocatalysis-chlorine activation for carbamazepine degradation by sulfur-doped NH2-MIL 53 (Fe) composites: Electronic modulation effect and the dual role of chlorine

Chlorine activation-inefficient and the generation of disinfection by-products (DBPs) has indeed limited the application of UV/chlorine process. In this study, the typical metal-organic frameworks (MOFs) NH2-MIL53(Fe) were successfully modified with organic ligands containing sulfur functional groups and applied to construct a novel UV-LED-driven heterogeneous chlorine activation system. The generation of intermediate energy levels and the charge redistribution effect on Fe-S bond facilitated the excitation of electrons and realized the effective separation of photohole (hvb+) and photoelectron (ecb-). The involvement of S-NH2-MIL53(Fe) improved the efficiency of UV-LED/chlorine process by 6 times. The effective activation of HOCl/OCl- by hvb+ and ecb- significantly enhanced the yield of HO· and Cl·. More importantly, HOCl/OCl- played a dual role in UV-LED/chlorine/S-NH2-MIL53(Fe) process as a precursor for the generation of free radicals and a catalyst for the enhancement of HO· yield, which could achieve efficient removal of the target pollutants at lower chlorine doses. In addition, the presence of low-valent sulfur species and ecb- accelerated the cycle of Fe(II)/Fe(III) and in-situ generation of HO· and Cl·. The known generation of DBPs in UV-LED/chlorine/S-NH2-MIL53(Fe) process decreased by 37.9% compared to UV-LED/chlorine process. Developing novel UV-LED/chlorine/S-NH2-MIL53(Fe) processes provided a reliable strategy to efficiently purify actual micro-polluted water bodies.

Rapid Inactivation of Fungal Spores in Drinking Water by Far-UVC Photolysis of Free Chlorine.

Effective and affordable disinfection technology is one key to achieving Sustainable Development Goal 6. In this work, we develop a process by integrating Far-UVC irradiation at 222 nm with free chlorine (UV222/chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV222/chlorine process achieves a 5.0-log inactivation of the A. niger spores at a chlorine dosage of 3.0 mg L-1 and a UV fluence of 30 mJ cm-2 in deionized water, tap water, and surface water. The inactivation rate constant of the spores by the UV222/chlorine process is 0.55 min-1, which is 4.6-fold, 5.5-fold, and 1.8-fold, respectively, higher than those of the UV222 alone, chlorination alone, and the conventional UV254/chlorine process under comparable conditions. The more efficient inactivation by the UV222/chlorine process is mainly attributed to the enhanced generation of reactive chlorine species (e.g., 6.7 × 10-15 M of Cl•) instead of hydroxyl radicals from UV222 photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV222 photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV222/chlorine process over the UV254/chlorine process also include the more effective inhibition of the photoreactivation of the spores after disinfection and the lower formation of chlorinated disinfection byproducts and toxicity.