Chlorine Consumption Research Articles

Optimization of chlorine consumption in water distribution networks by using the new ant colony optimization (ACOR) algorithm

Optimization of chlorine consumption in water distribution networks by using the new ant colony optimization (ACOR) algorithm

Overlooked Chlorination of Aqueous Alcohols: Aldehyde Formation and Artifactual Chlorine Consumption

Overlooked Chlorination of Aqueous Alcohols: Aldehyde Formation and Artifactual Chlorine Consumption

Study of the influence of temperature and duration of chlorinating roasting on the extraction of gold from E-waste

In this work, based on experimental studies, the effect of roasting temperature and duration on the chlorination of gold from E-waste under low-temperature conditions was studied. It has been established that in the low-temperature range of 150-300 °C, the gold content in the residue shows a sharp decrease, reaching its minimum of 8 ppm at 250 °C. A further increase in temperature does not affect the gold content in the cinder. It has been shown that during chlorinating roasting above a temperature of 250 °C, side reactions should be expected to occur with the formation of additional phases representing chlorides of copper, iron and other elements. The results of SEM and XRD analyzes of the solid phase obtained after chlorinating roasting at a temperature of 250 °C and a roasting duration of 20 minutes showed the presence of copper and iron chlorides in them. Optimal technological parameters and modes of the process of chlorinating roasting of E-waste with gaseous chlorine have been established: temperature – 250 °С; roasting duration – 20 minutes; chlorine consumption is 1.5 times more than the stoichiometrically required amount (SRA) for gold chlorination. Under optimal roasting conditions, a high, up to ~97.6%, recovery of gold in the form of gold chloride (AuCl3) was achieved. The results of the experiments can be a basic basis and make it possible to conduct more representative experiments (scaling) in the future, taking into account the established optimal technological parameters. This will provide a chance to evaluate the possibility of extracting gold from E-waste of different types and compositions and to conduct further research on obtaining pure gold from the collected representative amount of gold sublimate AuCl3 by smelting.

Optimizing the number, locations, and chlorine dosages of booster chlorination stations in water distribution networks

ABSTRACT Safe and reliable drinking water is essential for sustaining life. Chlorination is widely used for disinfection in water distribution networks (WDNs). A higher dose of chlorine is required in an overhead service reservoir to maintain minimum residual chlorine at the farthest end in WDNs. However, delivering high dosages of chlorine from storage tanks can pose public health issues, especially for the residents living near overhead service reservoirs due to the formation of trihalomethanes, haloacetic acids, and chlorophenols. In addition, a higher dosage will lead to increased chlorine consumption and will accelerate pipe corrosion. Booster chlorination (BC) stations with smaller dosages are a solution to this problem. However, identifying the optimal number, locations, and dosage of each BC station in a cost-effective manner is challenging. This study proposes a methodology for determining the optimal number, locations, and chlorine dosages of BC stations in WDNs using a mixed integer linear programming problem. The methodology is illustrated through a simplified WDN in Holeta town, Ethiopia. The results indicate that if one adds two BC stations beyond the three dosage stations at the source, it will lead to a 49% reduction in chlorine use and a 27% decrease in the life cycle cost.

A Self-Transformed N-Chlorinated ε-Polylysine Coating Endows Titanium Implants with Programmed Integration of Robust Antibacterial and Pro-Osteogenic Abilities

Implant-associated infection and poor osseointegration are the main causes of orthopedic implantation failure. For a long-term successful implantation, simultaneously introducing prevention of infection and promotion of osteogenesis into implants is highly desired but remains a grand challenge. Inspired by the human immune mechanism of tissue repair under bacterial infection, we propose a self-transformed strategy for the modification of titanium with porous N-chlorinated ε-polylysine coating (Ti-PL-NCl) through pore-making, surface grafting and chlorination. The as-prepared Ti-PL-NCl exhibits an excellent antibacterial activity against S. aureus and E. coli in the presence of N-chloramine in the early stage, with an antibacterial rate as high as 95.8% and 99.4%, respectively. With the consumption of oxidative chlorine, the N─Cl groups of Ti-PL-NCl are transformed into N─H groups with moderate antibacterial yet strong pro-osteogenic abilities. The self-transformed N-chlorinated ε-polylysine coating enables Ti-PL-NCl to achieve long-lasting antibacterial activity as well as enhanced pro-osteogenesis, thus providing adaptive bioactivities for bone-implant integration. Rat implant-associated osteomyelitis model confirms that Ti-PL-NCl has excellent efficacy of infection prevention and osseointegration promotion. This work may provide a new paradigm of designing multifunctional implants to achieve long-term successful implantation.

Lateral effects of infection prevention measures during COVID-19 pandemic on hospital-acquired Clostridioides difficile infection.

Background: Systematic surveillance of Clostridioides difficile infection (CDI) in our institution showed a reduction in the incidence of healthcare associated CDI (HA-CDI) during COVID-19 pandemic. Aim: Our objective was to search for factors related to this reduction. Methods: We retrospectively studied the trend of the incidences of HA-CDI, Multidrug Resistant (MDR) organisms, total antibiotic and chlorine consumptions as well as the influence of the last two on the incidence of HA-CDI. Results: During COVID-19 pandemic, the HA-CDI incidence was reduced with respect to the previous years, although total antibiotic consumption was found to increase (p < .01). MDR organisms' incidence was found to increase (p < .01), as well as the chlorine consumption (p = .04) which was the only factor to be related to the decreased rates of HA-CDI (r = -0.786, p < .05). Discussion: In our institution, COVID-19 epidemic overlapped with the reduction in the HA-CDI's incidence. This could be due to faithful compliance with the contact precaution measures but then, we would expect the incidence of MDR organisms to decrease as well. Chlorine usage for environmental cleaning was generalized during pandemic. It was the only factor to be related to the decreased rates of HA-CDI, highlighting the importance of environmental cleaning as a measure for HA-CDI prevention.

Synergistic effects of trace sulfadiazine and corrosion scales on disinfection by-product formation in bulk water of cast iron pipe

The effects of trace sulfadiazine (SDZ) and cast-iron corrosion scales on the disinfection by-product (DBP) formation in drinking water distribution systems (DWDSs) were investigated. The results show that under the synergistic effect of trace SDZ (10 μg/L) and magnetite (Fe3O4), higher DBP concentration occurred in the bulk water with the transmission and distribution of the drinking water. Microbial metabolism-related substances, one of the important DBP precursors, increased under the SDZ/Fe3O4 condition. It was found that Fe3O4 induced a faster microbial extracellular electron transport (EET) pathway, resulting in a higher microbial regrowth activity. On the other hand, the rate of chlorine consumption was quite high, and the enhanced microbial EET based on Fe3O4 eliminated the need for microorganisms to secrete excessive extracellular polymeric substances (EPS). More importantly, EPS could be continuously secreted due to the higher microbial activity. Finally, high reactivity between EPS and chlorine disinfectant resulted in the continuous formation of DBPs, higher chlorine consumption, and lower EPS content. Therefore, more attention should be paid to the trace antibiotics polluted water sources and cast-iron corrosion scale composition in the future. This study reveals the synergistic effects of trace antibiotics and corrosion scales on the DBP formation in DWDSs, which has important theoretical significance for the DBP control of tap water.

Formation of oxidation byproducts during electrochemical treatment of simulated produced water

Electrochemical oxidation (EO) can effectively remove recalcitrant organic contaminants from produced water (PW) but the formation of toxic oxidation byproducts (OBPs) is an unintended consequence. This study has rigorously investigated the OBPs formation during the EO treatment of a simulated PW containing phenol - a common organic contaminant existing in PW, as a model contaminant. In the absence of ammonia, free chlorine was generated from Cl- oxidation to serve as the main oxidant for phenol oxidation. During the EO process, 2,4,6-trichlorophenol and 2,6-dichlorobenzoquinone were identified as the critical intermediates that led to the formation of carbonaceous OBPs (C-OBPs). Some C-OBPs like chloroform (TCM), chloral hydrate (CH), and trichloroacetic acid (TCAA) reached their peak concentrations of 15 – 180 μM that were then reduced to 1 – 115 μM via volatilization and/or electrochemical reduction. When ammonia was present, nitrogenous OBPs (N-OBPs) were formed with the peak levels of 1 – 10 μM at the chlorination breakpoint (when ammonia was completely removed) that were subsequently reduced below 1 uM via volatilization and/or hydrolysis. It was observed that ammonia significantly decreased the formation of both C-OBPs and chlorate due to the consumption of free chlorine. A higher current density accelerated OBPs formation rates with different effects on volatile and non-volatile OBPs. The results of this study will enhance our understanding of OBPs formation precursors and mechanisms during electrochemical process and help develop strategies for proper control of OBPs to achieve safer electrochemical wastewater treatment.

Dynamical Integration of Antimicrobial, Anti‐Inflammatory, and Pro‐Osteogenic Activities on Polyetheretherketone via a Porous N‐Halamine Polymeric Coating

AbstractPolyetheretherketone (PEEK) has been widely used as orthopedic implants, but the poor antimicrobial and osseointegration properties hinder its advanced clinical applications. Most of the modification strategies are difficult to temporally fulfill initial broad‐spectrum antimicrobial and later pro‐osteogenic requirements for a long‐term success of implantation. N‐halamine is a kind of biofriendly antimicrobial agent, and its functional N─Cl groups could be converted into N─H groups, potentially resulting in new bioactivities. Therefore, it is supposed that N‐halamine might provide a feasible design for the dynamical integration of antimicrobial and pro‐osteogenic abilities. Herein, a new class of surface‐porous PEEK implant with an N‐halamine polymeric coating (sp‐PEEK‐NCl) is constructed by successive pore‐making, polymer grafting, and chlorination. The as‐prepared sp‐PEEK‐NCl exhibits broad‐spectrum antibacterial, antifungal, anti‐inflammatory, and pro‐osteogenic effects. More importantly, with the consumption of oxidative chlorine, the N─Cl groups in sp‐PEEK‐NCl are transformed into N─H groups with enhanced pro‐osteogenic ability, endowing sp‐PEEK‐NCl with dynamically compatible bioactivities for osseointegration in different periods after implantation. Rat implant‐associated osteomyelitis model confirms that sp‐PEEK‐NCl obviously reduces infectious bone destruction and promotes osseointegration in vivo. This work may provide a promising strategy for intelligent integration of bioactivities and valuable insight into the design of orthopedic implants in bone tissue engineering.

The mixed-order chlorine decay model with an analytical solution and corresponding trihalomethane generation model in drinking water

Ensuring effective drinking water disinfection, remaining a certain amount of residual chlorine, and controlling disinfection by-product formation were very important for guarantying water quality safety and protecting public health; thus, the chlorine decay model and corresponding disinfection by-product formation model were necessary. This paper proposed a mixed-order chlorine bulk decay model (two parameters) based on Taylor's formula and derived its analytical solution. The accuracy of the mixed-order model was evaluated by comparing it with the nth-order model. To optimize the model and reduce the number of parameters required to be calibrated, the relationship of parameters with temperature, initial chlorine concentration, TOC and inorganic substance (ammonia nitrogen and iodide ion) was explored. The result proved that one of the parameters could be regarded as temperature dependent only. Meanwhile, the temperature equation of the model parameters was established by the Arrhenius formula. Subsequently, this paper selected trihalomethane as the target and study the linear relationship between chlorine consumption and trihalomethane formation. The results indicated that the liner slope had little correlation with initial chlorine concentration and temperature. On this basis, the corresponding trihalomethane model was built and its performance was proven to be good. The modeling developed in this work could be applied to drinking water distribution systems for residual chlorine and trihalomethane prediction, and provided a reference for the decision involving water quality.

Silicon from sand is a promising technology for producing silicon of semiconductor quality

An analysis of the methods for obtaining silicon of semiconductor quality determined the relevance of the issues of compliance of modern technologies with environmental requirements of today, as well as the possibilities of raw materials and energy supply for a potential increase in production volumes. The development of production requires a search for compromises between the needs of society and the consequences expressed in the environmental impact on nature, the growth in the consumption of raw materials and energy. The proposal to use quartz sand instead of quartzite is promising due to the solution of the problems of raw material supply for the production of silicon of semiconductor quality for many years to come. The technology of chlorination of quartz sands proposed for implementation has been tested in industrial conditions and, in addition to the problems of raw material supply, to a large extent solves the problems of environmental and energy supply.Within the framework of the set environmental task, the problems of decarbonization of production are first of all solved by eliminating the energy-consuming high-temperature process of carbothermal reduction of silicon. The proposed technological solution provides a compromise between environmental friendliness and energy efficiency by involving silicon-containing materials, technogenic wastes, as “energy donors” in physical and chemical processes. Chlorination of the prepared raw materials is carried out in the solid phase, which is an energy-efficient solution, as it eliminates the cost of energy to compensate for the latent energy of melting. The initial preparation of raw materials involves the procedure of mechanoactivation - energy-efficient activation of the raw material by destroying intercrystalline bonds. The use of “energy donors” in blending ensures that the chlorination process is carried out in the autothermal mode, reducing the specific consumption of chlorine for the process. The problems of high energy intensity in the production of silicon of semiconductor quality are also solved by adjusting the technological scheme with the exclusion of energy-consuming low-temperature processes.The implementation of the proposed technological solutions is focused on the maximum use of known technological equipment, which minimizes the costs of design and production development of the technology. Based on the practical data obtained, system solutions for integrating the new technology into the schemes of existing enterprises are proposed - providing variability of adaptation in terms of raw material supply and the range of produced polycrystalline silicon of both “electronic” and “solar” quality. Based on the practical data obtained, system solutions were proposed for integrating the new technology into the schemes of existing enterprises - providing variability of adaptation in terms of raw material supply and the range of produced polycrystalline silicon of both “electronic” and “solar” quality.

Fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis to determine chlorine decay constants in urban water distribution system

This study applied a method for estimating chlorine decay constant (k) in urban water distribution systems using fluorescence excitation–emission matrix spectroscopy-parallel factor analysis (FEEM-PARAFAC), considering that it accounts for the influence of organic matter in the target area. The simultaneous impacts of seasonal variations on chlorine consumption and dissolved organic matter (DOM) composition were investigated for a year in three full-scale water distribution systems in I city (areas S, K, and G). Bulk decay constants (kb) were obtained through bottle tests, and the kb value was observed to differ by season and significantly affected by temperature. It exhibited its highest value, 0.794 d−1, in summer at area G. As a result of analyses through F-EEM-PARAFAC, it was determined that the components of the target raw water were humic-like and tryptophan-like. The quantitative analysis of organic substances through PARAFAC revealed that area G had the highest score (C1+C2) than other areas. 11.568, 10.578, and 11.771 in summer at areas S, K, and G, respectively. The model equations were derived such that the significant (R2 = 0.85–0.95) correlation between the C1 and C2 model scores and total chlorine decay constants (kt) verified via PARAFAC analysis of the target raw water was considered. Furthermore, a method for obtaining the wall decay constants at a target point based on the correlation equation was investigated.

Effects of UV-based oxidation processes on the degradation of microplastic: Fragmentation, organic matter release, toxicity and disinfection byproduct formation

The occurrence and transformation of microplastics (MPs) remaining in the water treatment plants has recently attracted considerable attention. However, few efforts have been made to investigate the behavior of dissolved organic matter (DOM) derived from MPs during oxidation processes. In this study, the characteristics of DOM leached from MPs during typical ultraviolet (UV)-based oxidation was focused on. The toxicity and disinfection byproduct (DBP) formation potentials of MP-derived DOM were further investigated. Overall, UV-based oxidation significantly enhanced the aging and fragmentation of highly hydroscopic MPs. The mass scales of leachates to MPs increased from 0.03% - 0.18% at initial stage to 0.09% - 0.71% after oxidation, which were significantly higher than those leached by natural light exposure. Combined fluorescence analysis with high resolution mass spectrometer scan confirmed that the dominant MP-derived DOM are chemical additives. PET-derived DOM and PA6-derived DOM showed inhibition of Vibrio fischeri activity with corresponding EC50 of 2.84 mg/L and 4.58 mg/L of DOC. Bioassay testing with Chlorella vulgaris and Microcystis aeruginosa showed that high concentrations of MP-derived DOM inhibited algal growth by disrupting the cell membrane permeability and integrity. MP-derived DOM had a similar chlorine consumption (1.63 ± 0.41 mg/DOC) as surface water (1.0 - 2.0 mg/DOC), and MP-derived DOM mainly served as precursors for the investigated DBPs. Contrary to the results of previous studies, the DBP yields from MP-derived DOM were relatively lower than those of aquatic DOM under simulated distribution system conditions. This suggests that MP-derived DOM itself rather than serving as DBP precursor might be potential toxic concern.

Reduction of Chlorine Disinfection Dosage through Optimal Jet Design in the Hong Kong Harbor Area Treatment Scheme

Chlorine is commonly used in disinfection processes in wastewater treatment plants. The chlorine solution is typically dosed by turbulent mixing through multiport jet diffusers. The chlorine reacts with the inorganic and organic nitrogenous compounds at a fast rate (in the order of 1 s or less), and a significant portion of the dosed chlorine can be rapidly consumed by the reactions instead of destroying the pathogens. Despite extensive previous research, the chlorine consumption in the complex sewage flow remains an elusive problem. Field-scale experiments have been carried out to study the chlorine consumption in the turbulent mixing of dense chlorine jets with the primary treated sewage effluent of the Stonecutter’s Island Sewage Treatment Works (serving a population of 5.7 million). Based on jet theory and the field tests, it is proposed to discharge the chlorine jets at a location of highest velocity to minimize the contact time of the sewage with high concentration chlorine. Full-scale in-plant experiments demonstrated that significant savings in chlorine can be achieved with optimal jet diffuser design and placement; at nominal applied chlorine dosages of 12 and 20 mg/L in winter and summer, respectively, the chlorine demand can be reduced by up to 30% compared with the conventional dosing design. The relatively simple dosing reconfiguration results in significant savings in chlorine and energy, reduces harmful impact to the environment, and improves plant operation reliability. The chlorine demands from daily operations are well-correlated with the results of the field-scale models. Predictions of the chlorine demand as a function of applied dosage and temperature were obtained from the collective field data.

Characterization and chlorine reactivity of particulate matter released by bathers in indoor swimming pools

Disinfecting swimming pool water is essential for preventing waterborne diseases. An unforeseen consequence of treating water with disinfectants is the formation of disinfection by-products (DPBs) that can cause harmful effects to health through the interactions between the added disinfectant and organic matter in the water. The present work focuses on the chlorine reactivity with particles released by bathers. Such particles are collected in the filter backwash water of swimming pools and this study intends to distinguish DPBs generated from dissolved chemicals from those formed by particulate matter. Therefore, filtered and unfiltered backwash waters were collected from several swimming pools, analysed physicochemically and chemically, and then chlorinated as is (79 mgL−1) and as diluted suspensions (36.2 and 11.9 mgL−1) at varying concentrations of chlorine (1.2 mg and 24 mgCl2L−1). Utilizing a DPD colorimetric technique and GC-ECD, respectively, the kinetics of chlorine consumption and DPBs production have been investigated. Up to 25.7 μgL−1 of chloroform was produced within 96 h at 1.2 mgCl2L−1, followed by haloacetic acids (HAAs) and haloacetonitriles (HANs). Within 96 h, the concentration of trichloroacetic acid reached a maximum of 231.8 μgL−1 at a chlorine concentration of 231.8 μgL−1. The formations of 0.13 μmol THMs, 0.31 μmol HAAs, and 0.04 μmol HANs per mg of dissolved organic carbon (DOC) were finally determined by correlating the organic content of particles with the nature of the DBPs generated. Comparing the quantities of DBPs generated in filtered and unfiltered samples helps us conclude that ∼50% of DBPs formed during the chlorination of swimming pool water are derived from particles brought by bathers.

Plasma-enhanced microbial electrolytic disinfection: Decoupling electro- and plasma-chemistry in plasma-electrolyzed oxidizing water using ion-exchange membranes

Pathogenic microorganisms pose a global threat to public health and environment. Common antibacterial chemicals produce toxic residues, inevitably harming the environment. Electrolyzed oxidizing water (EOW), a promising environment-friendly alternative disinfectant, still lacks effective production processes, sufficient bactericidal efficacy and stability, while the enabling physico-chemical mechanisms remain unclear. Here, we report, for the first time, an effective hybrid plasma electrochemical EOW production process and reveal the mechanisms by combining nonthermal plasmas and a two-chamber electrochemical cell separated by a cation exchange membrane (CEM) for decoupling the chemical reactions during the plasma treatment of water. Experimental results demonstrate that combined chlorine (chloramine) was the main chlorine product in the plasma-enhanced EOW (P-EOW) without a membrane, owing to the consumption of free chlorine (Cl2, HOCl, ClO−) by plasma-generated reactive nitrogen species. With a CEM in the plasma electrolysis system and through controlling the plasma discharge polarity, the production of free chlorine and other reactive species can be selectively controlled, with the highest concentration of free chlorine obtained in the negative plasma-enhanced EOW (NP-EOW). According to the transportation of cations by the CEM, the high concentrations of free chlorine may be attributed to the higher consuptions of H+ in cathode cell of negative plasma. The study of antibacterial ability of EOW produced under different conditions revealed that Staphylococcus aureus cells were best inactivated by the NP-EOW with CEM, which is mainly attributed to the higher concentration of free chlorine. This study demonstrates the feasibility of plasma-enhanced microbial electrolytic disinfection and offers new insights into the fundamental aspects of P-EOW chemistries for the future development of sustainable, efficient, and cost-effective multipurpose sustainable chemical technologies for water research and treatment.

Fertilization regime shifts the molecular diversity and chlorine reactivity of soil dissolved organic matter from tropical croplands

Soil-derived dissolved organic matter (SDOM) is an important site-specific disinfection byproduct (DBP) precursor in watersheds. However, it remains unclear how fertilization regime shifts the molecular diversity and chlorine reactivity of SDOM in cropland-impacted watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of the SDOM from croplands that had different fertilization regimes (i.e., non-fertilization, chemical fertilization, straw return, and chemical fertilization plus straw return) for 5 years and evaluated the chlorine reactivity of the SDOM by determining the 24-h chlorine consumption and specific DBP formation potential (SDBP-FP). The SDOM level decreased by chemical fertilization and was not significantly altered by straw return alone or combined with chemical fertilizer. However, all fertilization regimes elevated the molecular diversity of SDOM by increasing the abundance of protein-, lignin-, and tannin-like compounds. The chlorine reactivity of SDOM was reduced by chemical fertilization, but was significantly increased by straw return. Typically, straw return increased the formation potential of specific trihalomethane and chloral hydrate by 339% and 56% via increasing the aromatics in SDOM, whereas chemical fertilization could effectively decrease about 231% of the increased specific trihalomethane formation potential caused by straw return. This study highlights that fertilization regime can significantly shape the molecular diversity and chlorine reactivity of the SDOM in croplands and that partially replacing chemical fertilizer with crop straw is an advantageous practice for reducing DBP risks in drinking water in cropland-impacted watersheds.

Modeling the formation of disinfection byproducts in chlorinated swimming pool water: Role of body fluid analog

Abstract The recirculation of pool water and the continuous input of pollutants and disinfectants in swimming pools intensifies the accumulation of disinfection byproducts (DBPs), which have received increasing attention. Trihalomethanes (THMs) are the most common DBPs found in swimming pool water. Developing a predictive THM model is an efficient and promising way to optimize the chlorine dosage and guarantee water safety. Because the main components of swimmer inputs and their respective quantities have been formalized and determined through body fluid analogs (BFA), the model development can rely on the chlorination of BFA components and mixtures. In this study, a well-established second-order reaction chlorine decay model with a variable reaction rate coefficient was expanded to describe the chlorine consumption in swimming pool water. The THM model with a variable formation coefficient was first developed based on the identical assumption of the chlorine model, that is, the reactivity of the reactants decreases as the reaction progresses. The results showed that uric acid exhibited the fastest initial rate coefficient for chlorine decay. Although citric acid showed a considerably high specific THM formation potential (μmol-THM, species/mg productive chlorine consumption), urea and humic acid (HA) were attributed to the fast-reacting THM formation precursors. The rate coefficients of urea and HA were higher than that of citric acid. For the mixture, the (overall) reaction rate coefficients were formulated as a function of the rate coefficient of the individual substance and the concentration of the substance remaining in the water. This concept was tested using BFA and BFA with HA. The model accurately described the chlorine consumption and THM concentrations (R2 &amp;gt; 0.96).

Removal of trace organic pollutants and generation of halogenated disinfection by-products in membrane UV/chlorine combined process

In this study, the degradation kinetics and degradation mechanism of 23 trace organic pollutants (TrOCs) in the secondary effluent of sewage by the combined membrane-UV/chlorine process were investigated, and the halogenated disinfection by-products (X-DBPs) in the combined process were investigated and its generation potential (X-DBPsFP), and the cytotoxicity and genotoxicity of the treated water samples were also evaluated. The results showed that membrane pretreatment could effectively promote the degradation of TrOCs in UV/chlorine system, and nanofiltration (NF) was more effective than ultrafiltration (UF). Compared with UF, NF intercepts more dissolved organic matter (DOM), thus weakening the light shielding effect, chlorine consumption and radical quenching to a greater extent. It is found that the degradation mechanism of TrOCs can be divided into the following four categories: Ho˙ dominated, RHS dominated, chlorine and RHS jointly dominated and chlorine dominated. Membrane pretreatment can well reduce the formation of X-DBPs, among which UF and NF reduce the formation of haloacetamide (HAMs) and trihalomethanes (THMs) most significantly, while NF reduces the formation of X-DBPs and X-DBPsFP and the toxicity of water samples much stronger than UF. In addition, NF UV/chlorine can significantly remove the precursors of X-DBPs, so as to effectively control the enhancement of cytotoxicity and genotoxicity of water samples in the post chlorination process. The research results promote the development of advanced sewage treatment technology and provide theoretical guidance for related research.

Enhanced cyanogen chloride formation after UV/PS and UV/H2O2 pre-oxidation and chlorination in natural river water

Ultraviolet/persulfate (UV/PS) and Ultraviolet/hydrogen peroxide (UV/H2O2) have attracted much attention in recent years as advanced oxidation processes for water treatment. However, it is not all clear how these two methods affect the formation of cyanogen chloride (CNCl) in the subsequent water chlorination process. In this study, it was found that both UV/H2O2 and UV/PS pre-oxidation promoted the formation of CNCl in six actual water samples collected from urban rivers. Glycine, uric acid, arginine and histidine were investigated as the model compounds to explore the effects of different methods on the production of CNCl. The results showed that compared with chlorination alone, pre-oxidation by UV/H2O2 and UV/PS can reduce the production of CNCl for glycine and uric acid by up to 95% during post-chlorination process. However, they can greatly promote the formation of CNCl for arginine and histidine by up to 120-fold. In a more detailed investigation, pre-oxidation of histidine formed highly reactive intermediates to chlorine, leading to increased CNCl formation and chlorine consumption. The results showed that the precursors of CNCl was altered after pre-oxidation, and need to be re-evaluated.