Ce-doped TiO2 supported RuO2 as efficient catalysts for the oxidation of HCl to Cl2.

Reducing the cost of RuO2/TiO2 catalysts is still one of the urgent challenges in catalytic HCl oxidation. In the present work, a Ce-doped TiO2 supported RuO2 catalyst with a low Ru loading was developed, showing a high activity in the catalytic oxidation of HCl to Cl2. The results on some extensive characterizations of both Ce-doped TiO2 carriers and their supported RuO2 catalysts show that the doping of Ce into TiO2 can effectively change the lattice parameters of TiO2 to improve the dispersion of the active RuO2 species on the carrier, which facilitates the production of surface Ru species to expose more active sites for boosting the catalytic performance even under some harsh reaction conditions. This work provides some scientific basis and technical support for chlorine recycling.

A fast and sensitive colorimetric sensor for residual chlorine detection made with oxidized cellulose.

Residual chlorine from widespread disinfection processes forms byproducts in water that are harmful to humans and ecosystems. Portable sensors are essential tools for the on-site monitoring of residual chlorine in environmental samples. Here, an inexpensive colorimetric sensor was developed by grafting via amidation the chromogen orthotolidine (OTO) to the surface of a TEMPO-oxidized cellulose filter paper (O-TOFP). A thorough characterization of the sensor strip demonstrated that it was highly stable and that it could be stored for a long period before usage. O-TOFP had a fast response time of 30 s, was highly selective for residual chlorine ions (ClO-) with an accuracy of at least 95 %, and exhibited an excellent limit of detection of only 0.045 mg/L when combined with smartphone image acquisition. With its many positive features, the easy-to-use and robust O-TOFP sensor described here could become a useful tool for the determination of residual chlorine in different water samples.

Acidic process fluid from hydrothermal carbonization improves dechlorination of waste PVC and produces clean solid and liquid fuels.

Dechlorination of waste PVC (WPVC) by hydrothermal treatment (HTT) is a potential technology for upcycling WPVC in order to create non-toxic products. Literature suggests that acids can improve the HTT process, however, acid is expensive and also results in wastewater. Instead, the acidic process fluid (PF) of hydrothermal carbonization (HTC) of orange peel was utilized in this study to enhance the dechlorination of WPVC during HTT. Acidic HTT (AHTT) experiments were carried out utilizing a batch reactor at 300-350 °C, and 0.25-4 h. The finding demonstrated that the dechlorination efficiency (DE) is high, which indicates AHTT can considerably eliminate chlorine from WPVC and relocate to the aqueous phase. The maximum DE of 97.57 wt% was obtained at 350 °C and 1 h. The AHTT temperature had a considerable impact on the WPVC conversion since the solid yield decreases from 56.88 % at 300 °C to 49.85 % at 350 °C. Moreover, AHTT char and crude oil contain low chloride and considerably more C and H, leading to a considerably higher heating value (HHV). The HHV increased from 23.48 to 33.07 MJ/kg when the AHTT time was raised from 0.25 to 4 h at 350 °C, indicating that the AHTT time has a beneficial effect on the HHV. The majority fraction of crude oil evaporated in the boiling range of lighter fuels include gasoline, kerosene, and diesel (57.58-83.09 wt%). Furthermore, when the AHTT temperature was raised from 300 to 350 °C at 1 h, the HHV of crude oils increased from 26.11 to 33.84 MJ/kg. Crude oils derived from AHTT primarily consisted of phenolic (50.47-75.39 wt%), ketone (20.1-36.34 wt%), and hydrocarbon (1.08-7.93 wt%) constituents. In summary, the results indicated that AHTT is a method for upcycling WPVC to clean fuel.

Atmospheric chemistry of CF3CHFCF2OCH3 (HFE-356mec3) and CHF2CHFOCF3 (HFE-236ea1) initiated by OH and Cl and their contribution to global warming.

The kinetic study of the gas-phase reactions of hydroxyl (OH) radicals and chlorine (Cl) atoms with CF3CHFCF2OCH3 (HFE-356mec3) and CHF2CHFOCF3 (HFE-236ea1) was performed by the pulsed laser photolysis/laser-induced fluorescence technique and a relative method by using Fourier Transform infrared (FTIR) spectroscopy as detection technique. The temperature dependences of the OH-rate coefficients (kOH(T) in cm3s-1) between 263 and 353 K are well described by the following expressions: 9.93 × 10-13exp{-(988 ± 35)/T}for HFE-356mec3 and 4.75 × 10-13exp{-(1285 ± 22)/T} for HFE-236ea1. Under NOx-free conditions, the rate coefficients kCl at 298 K and 1013 mbar (760 Torr) of air were determined to be (2.30 ± 1.08) × 10-13 cm3s-1and (1.19 ± 0.10) × 10-15 cm3s-1, for HFE-356mec3 and HFE-236ea1, respectively. Additionally, the relative kinetic study of the Cl + CH2ClCHCl2 reaction was investigated at 298 K, as it was used as a reference reaction in the kinetic study of the Cl-reaction with HFE-356mec3 and discrepant rate coefficients were found in the literature. The global atmospheric lifetimes were estimated relative to CH3CCl3 at the tropospheric mean temperature (272 K) as 1.4 and 8.6 years for HFE-356mec3 and HFE-236ea1, respectively. These values combined with the radiative efficiencies for HFE-356mec3 and HFE-236ea1 derived from the measured IR absorption cross sections (0.27 and 0.41 W m-2 ppv-1) yield global warming potentials at a 100-yrs time horizon of 143 and 1473, respectively. The contribution of HFE-356mec3 and HFE-236ea1 to global warming of the atmosphere would be large if they become widespread increasing their atmospheric concentration.

UV-induced reactive species dynamics and product formation by chlorite.

Chlorite (ClO2-) is a regulated byproduct of chlorine dioxide water treatment processes. The transformation of chlorite under UV irradiation into chloride (Cl-) and chlorate (ClO3-) involves reactive species chain reactions that could enhance chlorine dioxide water treatment efficiency while reducing residual chlorite levels. This study conducted a mechanistic investigation of chlorite phototransformation by analyzing reaction intermediates and stable end products, including chlorine dioxide (ClO2), free chlorine (HOCl/OCl-), hydroxyl­radical (•OH), Cl-, and ClO3- through combined experimental and modeling approaches. Experiments were performed at UV254 irradiation in pure buffered water within the pH range of 6 to 8. Results indicated that the apparent quantum yields for chlorite phototransformation increased from 0.86 to 1.45, and steady-state •OH concentrations at 1 mM initial chlorite concentration rose from 8.16 × 10-14 M - 16.1 × 10-14 M with decreasing pH values. It was observed that under UV irradiation, chlorite acts as both a significant producer and consumer of reactive species through three distinct reaction pathways. The developed kinetic model, which incorporates optimized intrinsic chlorite quantum yields Φchloritein ranging from 0.33 to 0.39, effectively simulated the loss of oxidants and the formation of major products. It also accurately predicted steady-state concentrations of various species, including •OH, •ClO, Cl• and O3. For the first time, this study provides a comprehensive transformation pathway scheme for chlorite phototransformation. The findings offer important insights into the mechanistic aspects of product and oxidizing species formation during chlorite phototransformation.

Degradation and detoxification of ribavirin by UV/chlorine/Fe(II) process in water treatment system.

Ribavirin (RBV), which is extensively used to treat viral diseases such as COVID-19, is considered one of the major emerging contaminants due to its long-term existence and health risk in the aqueous environmental system. However, research on effective removal of RBV still remains insufficient. In this study, we investigated the RBV degradation kinetics and mechanism in UV/chlorine/Fe(II) process. The degradation rate constant kobs-RBV of RBV was 2.52 × 10-4 s-1 in UV/chlorine/Fe(II) process, which increased by 1.6 times and 1.3 times than that in chlorine alone and UV/chlorine process, respectively. Notably, trace amount Fe(II) promoted RBV degradation in UV/chlorine system through Fe2+/Fe3+ cycles, enhancing the yield of reactive species such as HO· and certain species reactive chlorine radicals (RCS). The contributions of HO· and RCS toward RBV degradation were 53.91% and 16.11%, respectively. Specifically, Cl·, ClO·, and Cl2·- were responsible for 8.59%, 2.69%, and 4.83% of RBV removal. The RBV degradation pathway indicated that the reactive species preferentially attacked the amide moiety of RBV, which cleaved the ether bond and the hydroxyl group. The toxicity evaluation of RBV degradation products elucidated that UV/chlorine/Fe(II) process was beneficial for RBV detoxification.

Complexation with Metal Ions Affects Chlorination Reactivity of Dissolved Organic Matter: Structural Reactomics of Emerging Disinfection Byproducts.

Metal ions are liable to form metal-dissolved organic matter [dissolved organic matter (DOM)] complexes, changing the chemistry and chlorine reactivity of DOM. Herein, the impacts of iron and zinc ions (Fe3+ and Zn2+) on the formation of unknown chlorinated disinfection byproducts (Cl-DBPs) were investigated in a chlorination system. Fe3+ preferentially complexed with hydroxyl and carboxyl functional groups, while Zn2+ favored the amine functional groups in DOM. As a consequence, electron-rich reaction centers were created by the C-O-metal bonding bridge, which facilitated the electrophilic attack of α-C in metal-DOM complexes. Size-reactivity continuum networks were constructed in the chlorination system, revealing that highly aromatic small molecules were generated during the oxidation and decarbonization of metal-DOM complexes. Molecular transformation related to C-R (R represents complex sites) loss was promoted via metal complexation, including decarboxylation and deamination. Consequently, complexation with Fe3+ and Zn2+ promoted hydroxylation by the C-O-metal bonding bridge, thereby increasing the abundances of unknown polychlorinated Cl-DBPs by 9.6 and 14.2%, respectively. The study provides new insights into the regulation of DOM chemistry and chlorine reactivity by metal ions in chlorination systems, emphasizing that metals increase the potential health risks of drinking water and more scientific control standards for metals are needed.

Full-length 16S rRNA gene sequencing reveals the operating mode and chlorination-aggravated SWRO biofouling at a nuclear power plant.

Reverse osmosis (RO) membrane fouling and biological contamination problems faced by seawater desalination systems are microbiologically related. We used full-length 16S rRNA gene sequencing to assess the bacterial community structure and chlorine-resistant bacteria (CRB) associated with biofilm growth in different treatment processes under the winter mode of a chlorinated seawater desalination system in China. At the outset of the winter mode, certain CRB, such as Acinetobacter, Pseudomonas, and Bacillus held sway over the bacterial community structure, playing a pivotal role in biofouling. At the mode's end, Deinococcus and Paracoccus predominated, with Pseudomonas and Roseovarius following suit, while certain CRB genera still maintained their dominance. RO and chlorination are pivotal factors in shaping the bacterial community structure and diversity, and increases in total heterotrophic bacterial counts and community diversity in safety filters may adversely affect the effectiveness of subsequent RO systems. Besides, the bacterial diversity and culturable biomass in the water produced by the RO system remain high, and some conditionally pathogenic CRBs pose a certain microbial risk as a source of drinking water. Targeted removal of these CRBs will be an important area of research for advancing control over membrane clogging and ensuring water quality safety in the future.

Relationship between chlorine decay and nanobubble application in secondary treated wastewater.

There has been numerous research on the uses of treated wastewater that needs chlorine disinfection, but none have looked at the impacts of injecting nanobubbles (NBs) on the decomposition of residual chlorine. Gas NB injection in treated wastewater improves its properties. The kinetics of disinfectant decay could be impacted by changes in treated wastewater properties. This paper studies the effect of various NB injections on the residual chlorine decay of secondary treated wastewater (STWW). It also outlines the empirical equations that were developed to represent these impacts. The results show that each type of NBs in treated wastewater had a distinct initial chlorine concentration. The outcomes demonstrated a clear impact on the decrease of the needed chlorine quantity and the reduction of chlorine decay rate when utilizing NB injection for the STWW. As a result, the residual chlorine will remain for a longer time and will resist any microbiological growth under the application of NBs on treated wastewater. Moreover, NBs in secondary treated effluent reduce chlorine usage, lowering wastewater disinfection costs.

In Situ Preparation of Chlorine-Regenerable Antimicrobial Polymer Molecular Sieve Membranes.

Microbial contamination has profoundly impacted human health, and the effective eradication of widespread microbial issues is essential for addressing serious hygiene concerns. Taking polystyrene (PS) membrane as an example, we herein developed report a robust strategy for the in situ preparation of chlorine-regenerable antimicrobial polymer molecular sieve membranes through combining post-crosslinking and nucleophilic substitution reaction. The cross-linking PS membranes underwent a reaction with 5,5-dimethylhydantoin (DMH), leading to the formation of polymeric N-halamine precursors (PS-DMH). These hydantoinyl groups within PS-DMH were then efficiently converted into biocidal N-halamine structures (PS-DMH-Cl) via a simple chlorination process. ATR-FTIR and XPS spectra were recorded to confirm the chemical composition of the as-prepared PS-DMH-Cl membranes. SEM analyses revealed that the chlorinated PS-DMH-Cl membranes displayed a rough surface with a multitude of humps. The effect of chlorination temperature and time on the oxidative chlorine content in the PS-DMH-Cl membranes was systematically studied. The antimicrobial assays demonstrated that the PS-DMH-Cl membranes could achieve a 6-log inactivation of E. coli and S. aureus within just 4 min of contact time. Additionally, the resulting PS-DMH-Cl membranes exhibited excellent stability and regenerability of the oxidative chlorine content.

Impact of Molecular Chlorine Production from Aerosol Iron Photochemistry on Atmospheric Oxidative Capacity in North China.

Elevated levels of atmospheric molecular chlorine (Cl2) have been observed during the daytime in recent field studies in China but could not be explained by the current chlorine chemistry mechanisms in models. Here, we propose a Cl2 formation mechanism initiated by aerosol iron photochemistry to explain daytime Cl2 formation. We implement this mechanism into the GEOS-Chem chemical transport model and investigate its impacts on the atmospheric composition in wintertime North China where high levels of Cl2 as well as aerosol chloride and iron were observed. The new mechanism accounts for more than 90% of surface air Cl2 production in North China and consequently increases the surface air Cl2 abundances by an order of magnitude, improving the model's agreement with observed Cl2. The presence of high Cl2 significantly alters the oxidative capacity of the atmosphere, with a factor of 20-40 increase in the chlorine radical concentration and a 20-40% increase in the hydroxyl radical concentration in regions with high aerosol chloride and iron loadings. This results in an increase in surface air ozone by about 10%. This new Cl2 formation mechanism will improve the model simulation capability for reactive chlorine abundances in the regions with high emissions of chlorine and iron.

Synthesis, fungal biotransformation, and evaluation of the antimicrobial potential of chalcones with a chlorine atom.

Chalcones are intermediate products in the biosynthesis of flavonoids, which possess a wide range of biological properties, including antimicrobial and anticancer activities. The introduction of a chlorine atom and the glucosyl moiety into their structure may increase their bioavailability, bioactivity, and pharmacological use. The combined chemical and biotechnological methods can be applied to obtain such compounds. Therefore, 2-chloro-2'-hydroxychalcone and 3-chloro-2'-hydroxychalcone were synthesized and biotransformed in cultures of two strains of filamentous fungi, i.e. Isaria fumosorosea KCH J2 and Beauveria bassiana KCH J1.5 to obtain their novel glycosylated derivatives. Pharmacokinetics, drug-likeness, and biological activity of them were predicted using cheminformatics tools. 2-Chloro-2'-hydroxychalcone, 3-chloro-2'-hydroxychalcone, their main glycosylation products, and 2'-hydrochychalcone were screened for antimicrobial activity against several microbial strains. The growth of Escherichia coli 10,536 was completely inhibited by chalcones with a chlorine atom and 3-chlorodihydrochalcone 2'-O-ß-D-(4″-O-methyl)-glucopyranoside. The strain Pseudomonas aeruginosa DSM 939 was the most resistant to the action of the tested compounds. However, chalcone aglycones and glycosides with a chlorine atom almost completely inhibited the growth of bacteria Staphylococcus aureus DSM 799 and yeast Candida albicans DSM 1386. The tested compounds had different effects on lactic acid bacteria depending on the tested species. In general, chlorinated chalcones were more effective in the inhibition of the tested microbial strains than their unchlorinated counterparts and aglycones were a little more effective than their glycosides.

Changes in combined toxicity of benzophenone-3 and humic acid on Daphnia magna and zebrafish during chlorination disinfection process.

Conventional wastewater treatment methods cannot completely remove the ultraviolet (UV) filters or dissolved organic matter. The transformation characteristics of these substances during chlorination disinfection and the varying species-specific toxicities of their combinations remain unclear. Here, Daphnia magna and zebrafish were exposed to benzophenone-3 (BP-3) and humic acid (HA) before and after chlorination disinfection. The results from chemical indicators showed that chlorination treatment decreased UV254 values and changed the intensity of parallel factors in three-dimensional fluorescence. Based on chemical analysis, the chlorine concentration and chlorination time for the toxicity experiments were set at 5 mg/L and 6 h, respectively. Exposure to HA and BP-3 before and after chlorination decreased the heart rate (by 1.37-28.12 %) in both species. However, species-specific responses, including survival rate, swimming distance, and expression of genes related to neurodevelopment, growth, and oxidative stress, were induced by chlorination. Chlorination reduced the impact of HA exposure but worsened the effects of HA and BP-3 co-exposure on D. magna. However, in zebrafish, the toxic effects intensified in most of the exposure groups after chlorination. Correlation analysis showed that the parallel factors of three-dimensional fluorescence were correlated with toxic effects on zebrafish, whereas UV254 was more significantly correlated with toxic effects on D. magna. This study provides insights into the combined toxicity of UV filters and dissolved organic matter in different aquatic organisms during chlorination, which is useful for risk control and optimization of the chlorination process.

Correlation between disinfection efficacy and cumulative amount of free chlorine reaching various positions during ultrasonic fogging with hypochlorite solution.

When a hypochlorite solution is ultrasonically fogged in a room, free chlorine, i.e., HOCl and OCl-, reaches various positions in two forms: fine fog droplets and gaseous hypochlorous acid（HOCl(g)）. In this study, the cumulative amount of free chlorine reaching various positions on the floor away from the fogger was measured in a 90-m3 room, using a sulfamate-carrying glass-fiber filter indicator. The fine droplets were blown out from the fogger into the spaces at different discharge port angles of 30 - 90°. Free chlorine was successfully trapped by sulfamate, forming monochlorosulfamate, which was stably retained on the indicator. The cumulative amount of free chlorine（ ng/indicator） increased with fogging time at each position and depended on the blow angle and distance from the fogger. Minor differences in the HOCl(g) concentration near the floor at all positions were observed. The disinfection efficacy of the fogging treatment against Staphylococcus aureus on wet surfaces was relatively higher at positions near the fogger and lower at positions far from the fogger. At each discharge port angle, a strong correlation between the logarithmic reduction in relative viable cells and the cumulative amount of free chlorine reaching S. aureus plates was observed. The slopes of the regression lines of correlation diagrams as a function of the cumulative amount of free chlorine were between -0.0362 and -0.0413 ng-1. This study demonstrated that the cumulative amount of free chlorine measured using the filter indicator could reflect the sum of the free chlorine of both fine droplets and HOCl(g), and that the disinfection efficiency depended on the cumulative amount of free chlorine reaching different areas.

A combined experimental and computational investigation on the OH radical and Cl atom-initiated reaction of 2,3-dichloropropene in troposphere.

Temperature-dependent kinetics of OH radical and Cl atom-initiated reaction of an important halogenated alkene, 2,3-Dichloropropene (23DCP), were investigated using absolute and relative methods over 278-363 K. Pulsed laser photolysis - laser induced fluorescence technique and relative rate method using gas chromatography with flame ionization detector were employed for studying the kinetics of 23DCP with OH radical and Cl atom, respectively. The obtained Arrhenius expressions were kOH(expt)=(4.08 ± 1.63) × 10-13exp{(1043 ± 124)/T} cm3 molecule-1 s-1 and kCl(expt)=(1.54 ± 0.24) × 10-11exp{(705 ± 48)/T} cm3 molecule-1 s-1. Computational calculations were conducted to validate our experimental kinetic results and provide new insights into the importance of a particular pathway among all based on thermodynamic parameters. The addition of OH/Cl to the terminal carbon of the double bond present in 23DCP proved to be the predominant pathway across the selected temperature range for the present study (200-400 K). The degradation mechanism of these reactions was proposed by analyzing the products with the aid of gas chromatography with mass spectrometry. Calculating various atmospheric implication parameters can help to understand how the release of 23DCP may affect the troposphere.

VUV coupled with low-dose H2O2 as pretreatment prior to UF: Performance, mechanisms, DBPs formation and toxicity evaluation.

Ultrafiltration (UF) is widely used in drinking water plants; however, membrane fouling is unavoidable. Natural organic matter (NOM) is commonly considered as an important pollutant that causes membrane fouling. Herein, we proposed VUV/H2O2 as a UF pretreatment and used UV/H2O2 for comparison. Compared to UV/H2O2, the VUV/H2O2 system presented superior NOM removal. In the VUV/H2O2 system, the steady-state concentration of HO• was approximately twice that in the UV/H2O2 system, which was ascribed to the promoting effect of the 185 nm photons. Specifically, 185 nm photons promoted HO• generation by decomposing mainly H2O at a low H2O2 dose or by decomposing mainly H2O2 at a high H2O2 dose. The VUV/H2O2 pretreatment also demonstrated better membrane fouling mitigation performance than did UV/H2O2. An increase in the H2O2 dose promoted HO• generation, thereby enhancing the performance of NOM degradation and membrane fouling alleviation and shifting the major membrane fouling mechanism from cake filtration to standard blocking. The VUV/H2O2 (0.60 mM) pretreatment effectively reduced disinfection byproducts (DBPs) formation during chlorine disinfection. Additionally, the oxidant H2O2 affected the membrane surface morphology and performance but had no evident effect on the mechanical properties. In actual water treatment, the VUV/H2O2 pretreatment exhibited better performance than the UV/H2O2 pretreatment in easing membrane fouling, ameliorating water quality, and reducing DBPs formation and acute toxicity.

A new concern raised from algal bloom: Organic chloramines in chlorination.

Algal blooms have become a significant challenge in water treatment all over the world. In chlorination of drinking water, algal organic matter (AOM) leads to the formation of organic chloramines. The objectives of this review are to comprehensively summarize and discuss the up-to-date researches on AOM-derived organic chloramines and their chemical activities and toxicity, thereby drawing attention to the potentially chemical and hygienic risks of organic chloramines. The predominant algal species in water sources varied with location and season. AOM from cyanobacteria, green algae, and diatoms are composed of diverse composition. AOM-derived amino acids take a low portion of the precursors of organic chloramines. Both experimental kinetic data and quantum chemical calculation demonstrate the preferential formation of organic chloramines in the chlorination of model compounds (amino acids and peptides). Organic chloramines are persistent in water and can transform into dichloro- and trichloro-organic chloramines, unknown low-molecular-weight organic chloramines, and nitrogenous disinfection byproducts with the excess of free chlorine. The active chlorine (Cl+) in organic chloramines can lead to the formation of chlorinated phenolic compounds. Organic chloramines influence the generation and species of radicals and subsequent products in UV disinfection. Theoretical predictions and toxicological tests suggest that organic chloramines may cause oxidative or toxic pressure to bacteria or cells. Overall, organic chloramines, as one group of high-molecular-weight disinfection byproducts, have relatively long lifetimes, moderate chemical activities, and high hygienic risks to the public. Future perspectives of organic chloramines are suggested in terms of quantitative detection methods, the precursors from various predominant algal species, chemical activities of organic chloramines, and toxicity/impact.

Comparison of chlorine and chlorine dioxide disinfection in drinking water: Evaluation of disinfection byproduct formation under equal disinfection efficiency.

Disinfection efficiency and disinfection byproduct (DBP) formation are two important aspects deserving careful consideration when evaluating different disinfection protocols. However, most of the previous studies on the selection of disinfection methods by comparing DBP formation were carried out under the same initial/residual dose and contact time of different disinfectants, and such a practice may cause overdose or underdose of a certain disinfectant, leading to the inaccurate evaluation of disinfection. In this study, a comprehensive and quantitative comparison of chlorine (Cl2) and chlorine dioxide (ClO2) disinfection was conducted with regard to their DBP formation under equal disinfection efficiency. The microbial inactivation models as well as the Cl2 and ClO2 demand models were developed. On such basis, the integral CT (ICT) values were determined and used as a bridge to connect disinfection efficiency and DBP formation. For 3-log10 and 4-log10 reductions of Pseudomonas aeruginosa, ClO2 had 1.5 and 5.8 times higher inactivation ability than Cl2, respectively. In the premise of equal disinfection efficiency (i.e., the ICT ratios of Cl2 to ClO2 = 1.5 and 5.8), the levels of total organic chlorine, total organic bromine, and total organic halogen formed in the Cl2 disinfection were significantly higher than those formed in the ClO2 disinfection. Among the 35 target aliphatic DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs) were the dominant species formed in both Cl2 and ClO2 disinfection. The total THM levels formed in Cl2 disinfection were 14.6 and 30.3 times higher than those in ClO2 disinfection, respectively. The total HAA levels formed in Cl2 disinfection were 3.5 and 5.4 times higher than those in ClO2 disinfection, respectively. Formation of the target 48 aromatic DBPs was much favored in Cl2 disinfection than that in ClO2 disinfection, and the formation levels was dominated by contact time. This study demonstrated that ClO2 had significant advantages over Cl2, especially at higher microorganism inactivation and lower DBP formation requirements.

Effects of Fe(III) on the formation and toxicity alteration of halonitromethanes, dichloroacetonitrile, and dichloroacetamide from polyethyleneimine during UV/chlorine disinfection.

Trace iron ions (Fe(III)) are commonly found in water and wastewater, where free chlorine is very likely to coexist with Fe(III) affecting the disinfectant's stability and N-DBPs' fate during UV/chlorine disinfection, and yet current understanding of these mechanisms is limited. This study investigates the effects of Fe(III) on the formation and toxicity alteration of halonitromethanes (HNMs), dichloroacetonitrile (DCAN), and dichloroacetamide (DCAcAm) from polyethyleneimine (PEI) during UV/chlorine disinfection. Results reveal that the maxima concentrations of HNMs, DCAN, and DCAcAm during UV/chlorine disinfection with additional Fe(III) were 1.39, 1.38, and 1.29 times higher than those without additional Fe(III), instead of being similar to those of Fe(III) inhibited the formation of HNMs, DCAN and DCAcAm during chlorination disinfection. Meanwhile, higher Fe(III) concentration, acidic pH, and higher chlorine dose were more favorable for forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection, which were highly dependent on the involvement of HO· and Cl·. Fe(III) in the aquatic environment partially hydrolyzed to the photoactive Fe(III)­hydroxyl complexes Fe(OH)2+ and [Fe(H2O)6]3+, which undergone UV photoactivation and coupling reactions with HOCl to achieve effective Fe(III)/Fe(II) interconversion, a process that facilitated the sustainable production of HO·. Extensive product analysis and comparison verified that the HO· production enhanced by the Fe(III)/Fe(II) internal cycle played a primary role in increasing HNMs, DCAN, and DCAcAm productions during UV/chlorine disinfection. Note that the incorporation of Fe(III) increased the cytotoxicity and genotoxicity of HNMs, DCAN, and DCAcAm formed during UV/chlorine disinfection, and yet Fe(III) did not have a significant effect on the acute toxicity of water samples before, during, and after UV/chlorine disinfection. The new findings broaden the knowledge of Fe(III) affecting HNMs, DCAN, and DCAcAm formation and toxicity alteration during UV/chlorine disinfection.

Higher thermal remediation temperature facilitates the sequential bioaugmented reductive dechlorination.

The coupling of thermal remediation with microbial reductive dechlorination (MRD) has shown promising potential for the cleanup of chlorinated solvent contaminated sites. In this study, thermal treatment and bioaugmentation were applied in series, where prior higher thermal remediation temperature led to improved TCE dechlorination performance with both better organohalide-respiring bacteria (OHRB) colonization and electron donor availability. The 60 °C was found to be a key temperature point where the promotion effect became obvious. Amplicon sequencing and co-occurrence network analysis demonstrated that temperature was a more dominating factor than bioaugmentation that impacted microbial community structure. Higher temperature of prior thermal treatment resulted in the decrease of richness, diversity of indigenous microbial communities, and simplified the network structure, which benefited the build-up of newcoming microorganisms during bioaugmentation. Thus, the abundance of Desulfitobacterium increased from 0.11 % (25 °C) to 3.10 % (90 °C). Meanwhile, released volatile fatty acids (VFAs) during thermal remediation functioned as electron donors and boosted MRD. Our results provided temperature-specific information on synergistic effect of sequential thermal remediation and bioaugmentation, which contributed to better implementation of the coupled technologies in chloroethene-impacted sites.