Formation Of Disinfection By-products Research Articles

Improvements of ferrate(VI) pretreatment on membrane flux and membrane rejection using cheap NaClO reagent

Ferrate(VI) pretreatment can effectively alleviate membrane fouling during the ultrafiltration (UF) process, while instability and high expenditure limit its application. This study discovered that the cheap NaClO reagent would improve the performance of ferrate(VI) pretreatment, i.e., establishing Fe(VI)/NaClO (FC) process. 20 μM of Fe(VI) group can increase J/J0 from 0.323 to 0.391, while the optimization process of 20 μM Fe(VI)/4 μM NaClO [FC (5:1)] increased it to 0.491 at the end of cycle 1 filtration. Meanwhile, the reversible and irreversible membrane fouling resistance decreased by 50% and 56% in FC (5:1). This was attributed to the suppression of ferrate(VI) decomposing and in-situ formation of more dispersed ferric nanoparticles in FC process [730.33 nm in Fe(VI) and 606.80 nm in FC (5:1)] by applied NaClO. The rejection ratio of dissolved organic carbon (DOC) increased from 27.18% of Fe(VI) group to 40.34% of FC (5:1) due to the repulsive interaction amplification of acid-base (AB) interaction energy. That was derived from the hydrophilia promotion of the treated sample and the electrical property evolution of in-situ formed ferric nanoparticles by NaClO. It suggested that AB interaction energy, presenting repulsive interaction in membrane-foulants and foulants-foulants, was a major role in Fe(VI) group and FC process. There was no more side effect induced by FC pretreatment, which was confirmed by the result that FC caused no increase in the disinfection by-products (DBPs) formation potential. The present study provided insight into improving the effect of ferrate(VI) pretreatment without inducing side effect, and reduced the costs of ferrate(VI) pretreatment during the process of UF.

Developing a UV dosing strategy for UV/chlorine process towards the trade-off between pharmaceuticals and personal care products degradation and disinfection by-products formation

In addition to UV wavelength and pH, UV irradiation intensity and fluence also play crucial roles in the UV/chlorine treatment of drinking water. This work aimed to develop a novel UV irradiation strategy to achieve a trade-off between pharmaceuticals and personal care products (PPCPs) degradation and disinfection by-products (DBPs) formation during UV/chlorine water treatment under a specific chlorine dose. Under high UV irradiation intensity at the same UV fluence, the faster chlorine photolysis produced higher steady-state concentrations of •Cl and •OH species but abated cumulative exposures of free available chlorine (CTFAC = ∫0t[Cl2]dt). As a result, the degradation rate of PPCPs was accelerated, but the removal percentage of some PPCPs decreased. Meanwhile, the degradation of the chromophores of dissolved organic matters (DOM) declined by 23.3%–24.8% under the higher UV irradiation intensity. Reducing CTFAC values (50.7%–57.6%) by high UV irradiation intensity could mitigate the formation of haloacetic acids, trihalomethanes and absorbable organic halogens (13.9%–14.9%), which addressed the key role of active chlorine in the formation of DBPs in the UV/chlorine process. DBPs were mainly generated from the interactions of DOM with reactive chlorine. The Vibrio fischeri data further indicated that increasing UV intensity reduced acute toxicity regardless of UV wavelength or water pH. For the same UV fluence dose, the high UV irradiation intensity can effectively control the trade-off between oxidation efficiency and DBPs formation during UV/chlorine treatment.

Ozonation of lake water and wastewater: Identification of carbonous and nitrogenous carbonyl-containing oxidation byproducts by non-target screening

Ozonation of drinking water and wastewater is accompanied by the formation of disinfection byproducts (DBPs) such as low molecular weight aldehydes and ketones from the reactions of ozone with dissolved organic matter (DOM). By applying a recently developed non-target workflow, 178 carbonous and nitrogenous carbonyl compounds were detected during bench-scale ozonation of two lake waters and three secondary wastewater effluent samples and full-scale ozonation of secondary treated wastewater effluent. An overlapping subset of carbonyl compounds (20%) was detected in all water types. Moreover, wastewater effluents showed a significantly higher fraction of N-containing carbonyl compounds (30%) compared to lake water (17%). All carbonyl compounds can be classified in 5 main formation trends as a function of increasing specific ozone doses. Formation trends upon ozonation and comparison of results in presence and absence of the •OH radical scavenger DMSO in combination with kinetic and mechanistic information allowed to elucidate potential carbonyl structures. A link between the detected carbonyl compounds and their precursors was established by ozonating six model compounds (phenol, 4-ethylphenol, 4-methoxyphenol, sorbic acid, 3-buten-2-ol and acetylacetone). About one third of the detected carbonous carbonyl compounds detected in real waters was also detected by ozonating model compounds.Evaluation of the non-target analysis data revealed the identity of 15 carbonyl compounds, including hydroxylated aldehydes and ketones (e.g. hydroxyacetone, confidence level (CL) = 1), unsaturated dicarbonyls (e.g. acrolein, CL = 1; 2-butene-1,4-dial, CL = 1; 4-oxobut-2-enoic acid, CL = 2) and also a nitrogen-containing carbonyl compound (2-oxo-propanamide, CL =1).Overall, this study shows the formation of versatile carbonous and nitrogenous carbonyl compounds upon ozonation involving ozone and •OH reactions. Carbonyl compounds with unknown toxicity might be formed, and it could be demonstrated that acrolein, malondialdehyde, methyl glyoxal, 2-butene-1,4-dial and 4-oxo-pentenal are degraded during biological post-treatment.

The change of amino acids samples under metalimnetic oxygen minimum condition: Characterization and mechanism

The metalimnetic oxygen minimum (MOM) is a common anaerobic phenomenon that occur between 5.00 and 40.00 m of reservoirs. Amino acids (AAs) are widely found in water, but their change in MOM remain unclear. In this study, four AAs with different side chain groups were selected to explore the change of their samples and related disinfection by-products formation potential (DBPFPs) under MOM condition. The results showed that the final degradation rate of dissolved organic carbon and dissolved organic nitrogen of four AAs samples were 11.71%−59.87% and 26.50%−100.00% under MOM condition. Aspartic acid samples were the easiest to be degraded, whereas glycine samples were the opposite. While the total fluorescence intensity increased by 6.30%−113.40% for the appearance of tryptophan-like substance. The total DBPFPs of glutamic acid, arginine and aspartic acid samples were finally decreased by 4.73%, 8.00% and 98.88% (glycine sample increased by 2.30 times). Compared with the surface condition, the degradation of AAs samples and the change of DBPFPs were significantly inhibited under MOM condition. In addition, the diversities of bacterial communities were significantly reduced under MOM condition, which was very unfavorable to the degradation of AAs samples, and in turn affected the control of DBPs and deteriorated the water quality.

Degradation of iopamidol in the permanganate/sulfite process: Evolution of iodine species and effect on the subsequent formation of disinfection by-products

Permanganate/sulfite (Mn(VII)/S(IV)) process is a promising pre-oxidation technology for sequestering the emerging organic contaminants in drinking water treatment plant. Iopamidol (IPM), a representative of iodinated X-ray contrast media, has been widely detected in water sources and has the risk of forming iodinated disinfection byproducts (I-DBPs) in water treatment system. In this study, we investigated the evolution of iodine species during the IPM degradation by the Mn(VII)/S(IV) process and its effect on the subsequent formation of I-DBPs during chlorination at pH 7.0 and 8.0. IPM could be effectively degraded in the Mn(VII)/S(IV) process at environmentally relevant pH (pH 7.0 and 8.0). The results of quenching and competitive oxidation kinetic experiments revealed that SO4·– was the major reactive oxidizing species contributing to the degradation of IPM whereas the contributions of HO· and reactive manganese species were negligible in the Mn(VII)/S(IV) process. I– and IO3– were generated while no HOI was detected during the degradation of IPM in the Mn(VII)/S(IV) process. The effects of IPM oxidation by Mn(VII)/S(IV) on the subsequent formation of chlorinated disinfection by-products (Cl-DBPs) during chlorination were related to the category of Cl-DBPs. The pre-oxidation of IPM by Mn(VII)/S(IV) resulted in the generation of I-DBPs during the disinfection process although no I-DBPs were detected if no pre-oxidation was applied. The finding of this study suggested that attention should be paid to the toxicity of DBPs when water containing iodinated organic contaminants is treated by Mn(VII)/S(IV) process or other pre-oxidation technologies.

Bacterial diversity across four drinking water distribution systems in Croatia: impacts of water management practices and disinfection by-products.

Several factors may impact bacterial diversity in drinking water distribution systems (DWDSs) including the origin of the raw water, the water treatment technologies, and the disinfection practices applied. 16S rRNA metabarcoding was used for the in-depth characterization of bacterial communities in the four studied Croatian DWDSs (A, B, C, D) two of which had residual disinfectant (A, B) and two were without (C, D), while only B utilized the conventional water treatment technology. Significantly higher diversity and species richness were evidenced in non-disinfected DWDSs (p<0.05) compared to disinfected DWDSs. The phylum Proteobacteria was the most abundant in all the DWDSs, being proportionately higher in non-disinfected systems (p<0.05). The most abundant genera in DWDS-A Mycobacterium and Sphingomonas both positively correlated, whereas Lactobacillus negatively correlated with the concentration of disinfection by-products (DBPs) as a sum of haloacetic acids (HAAs). Conversely, the genus Ralstonia positively correlated with the individual DBP dichloroacetic acid. These results indicate that genera Sphingomonas, Mycobacterium, Lactobacillus and Ralstonia could have an effect on promoting the formation of DBPs, in a similar manner to how negatively correlated taxa may influence their degradation.

Overlooked roles of Cl2O and Cl2 in micropollutant abatement and DBP formation by chlorination

This study investigated the roles of diverse free available chlorine (FAC) species including HOCl/OCl−, H2OCl+, Cl2O, and Cl2 in the degradation of micropollutants. The degradation of 5 micropollutants was significantly affected by pH, FAC dosage, and chloride (Cl−) concentration. The reaction orders in FAC (n) of 5 micropollutants (acetaminophen, carbamazepine, naproxen, gemfibrozil, and mecoprop) ranged from 1.4 ± 0.2 to 2.1 ± 0.3 at pH 3 − 5, evidencing the importance of Cl2O and Cl2 for micropollutant abatement. A simplified method for the determination of second-order rate constants (k) of specific FAC species with micropollutants was developed. Herein, the k for neutral/dissociated forms of 5 micropollutants with Cl2 and Cl2O were determined in the ranges of 9.3 (± 0.2) × 102 ∼ 2.9 (± 0.2) × 109 M−1 s−1 and 1.8 (± 0.1) × 104 ∼ 3.7 (± 0.6) × 109 M−1 s−1, respectively. They were 4 − 7 orders of magnitude higher than those of HOCl, whereas those of OCl− and H2OCl+ were negligible. By using kinetic modeling, Cl2 was more important under acidic conditions and higher Cl− levels with contributions of 37.9 – 99.2% at pH 5 in pure water. Cl2O played a dominant role in micropollutant degradation in pure water (56.4 − 87.3%) under neutral conditions. Furthermore, both Cl2 and Cl2O played vital roles in the formation of disinfection byproducts (DBPs) during chlorination of carbamazepine and natural organic matter. This study highlights the overlooked roles of Cl2O and Cl2 in micropollutant abatement and DBP formation during chlorination.

Changes in the structural characteristics of EfOM during coagulation by aluminum chloride and the effect on the formation of disinfection byproducts

The effects of coagulation on the removal efficiency of different fractions of effluent organic matter (EfOM) from wastewater treatment plants were investigated to identify changes in their structural characteristics and the influences on trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP). The results indicated that coagulation performed better for the removal of hydrophobic base (HOB) and hydrophobic neutral (HON) fractions than hydrophilic (HI) and hydrophobic acid (HOA) fractions. The removal efficiency was higher under neutral than under acidic conditions for all fractions. As a result, lower levels of THMFP and HAAFP were detected at pH7. The excitation-emission matrix spectra indicated that the HI fraction contained humic acid-like substances that reacted with chlorine to form THMs. The HON fraction contained soluble microbial byproduct-like substances with a higher potential to create HAAs. The results of Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-pressure size exclusion chromatography (HP-SEC) of the raw and coagulated water indicated that a higher molecular weight, α-carbon, COOH, aromatic structures, and polysaccharides were associated with a higher production of disinfection byproducts (DBP). These results elucidate the coagulation efficiencies of EfOM fractions associated with different mechanisms and facilitate the prediction of DBP formation by each fraction based on specific structural characteristics.

Formation of Larger Molecular Weight Disinfection Byproducts from Acetaminophen in Chlorine Disinfection.

Acetaminophen is widely used to treat mild to moderate pain and to reduce fever. Under the worldwide COVID-19 pandemic, this over-the-counter pain reliever and fever reducer has been drastically consumed, which makes it even more abundant than ever in municipal wastewater and drinking water sources. Chlorine is the most widely used oxidant in drinking water disinfection, and chlorination generally causes the degradation of organic compounds, including acetaminophen. In this study, a new reaction pathway in the chlorination of acetaminophen, i.e., oxidative coupling reactions via acetaminophen radicals, was investigated both experimentally and computationally. Using an ultraperformance liquid chromatograph coupled to an electrospray ionization-triple quadrupole mass spectrometer, we detected over 20 polymeric products in chlorinated acetaminophen samples, some of which have structures similar to the legacy pollutants "polychlorinated biphenyls". Both C-C and C-O bonding products were found, and the corresponding bonding processes and kinetics were revealed by quantum chemical calculations. Based on the product confirmation and intrinsic reaction coordinate computations, a pathway for the formation of the polymeric products in the chlorination of acetaminophen was proposed. This study suggests that chlorination may cause not only degradation but also upgradation of a phenolic compound or contaminant.

Effect of Medium Pressure Ultraviolet/Chlorine Advanced Oxidation on the Production of Disinfection by-Products from Seven Model Benzene Precursors

UV/chlorine advanced oxidation process (AOP), as a potential alternative to UV/H2O2 in water treatment, may pose a potential risk of increased disinfection by-product (DBP) formation and is of great concern. In this paper, seven benzene derivatives, containing two chlorine-inert and five chlorine-active compounds, were selected as typical model DBP precursors, and the effects of medium pressure UV/chlorine (MPUV/chlorine) on their chlorine demand and DBP formation potential (DBPFP) were evaluated. The results showed that MPUV/chlorine could significantly increase the chlorine demand and DBPFP of the two inert precursors. For the four slow but active DBP precursors, MPUV/chlorine may accelerate their short-term DBP formation, whereas it showed an insignificant effect or even reduced their chlorine demand and DBPFP. For the only fast and active DBP precursor, MPUV/chlorine showed an insignificant effect on its short-term DBP formation or DBPFP. The overall effect of MPUV/chlorine was more significant at pH 6 than at pH 8. In the presence of Br−, MPUV/chlorine significantly increased the bromine substitution factors of THMs. In addition, linear fitting results indicated that the UV/chlorine-induced change in overall chlorine demand may be considered as a potential indicator for the prediction of DBPFP alteration.

Correlation Analysis of the Carboxyl and Carbonyl Groups of Natural Organic Matter and the Formation Potential of Trihalomethanes and Chloral Hydrate

Natural organic matter (NOM) has always been considered the main precursor of disinfection by-products (DBPs) during the chlorine disinfection of drinking water. This research focuses on investigating the correlation between the functional group (carboxyl and carbonyl groups) content of NOM and the formation of trichloromethane (TCM) and chloral hydrate (CH). The quantitative determination of carboxyl groups, carbonyl groups, TCM, and CH were conducted during the drinking water treatment processes with different coagulant dosages and with/without pre-oxidation by KMnO4 or NaClO. The most appropriate coagulant for the removal of conventional components was polyaluminum chloride (PAC), and the dosage was 110 mg/L. Up to 43.7% and 14.5% of the carboxyl and carbonyl groups, respectively, were removed through the coagulation and sedimentation processes, which can be enhanced by increasing PAC dosage. The filtration process further increased the removal rates of these two functional groups to 59.8% and 33.5%, respectively. The formation potential of the TCM and CH decreased as the PAC dosage increased. Pre-oxidation by KMnO4 (0.8-1.0 mg/L) effectively controlled the formation of DBPs while increasing the carboxyl and carbonyl group content. Pre-oxidation by NaClO decreased the formation of TCM rather than CH, and a suitable amount (0.5-1.0 mg/L) decreased the carboxyl and carbonyl groups. It was found that there was a good linear correlation between carboxyl groups and TCM and CH. The linear fit R2 values of the carboxyl groups to TCM and CH were 0.6644 and 0.7957, respectively. The linear fit R2 values of the carbonyl groups to TCM and CH were 0.5373 and 0.7595, respectively.

Hydrochloric acid-modified algal biochar for the removal of Microcystis aeruginosa: Coagulation performance and mechanism

The unceasing algae blooms have led to the deterioration of water quality and ecological imbalance in the entire globe, it’s urgent to investigate its treatment and resource utilization technology. In this study, treated algae was prepared to produce the biochar and then it was utilized as a coagulant for the removal of Microcystis aeruginosa. To improve the pore structure of algae-derived biochar for improving the removal capacity of M. aeruginosa, hydrochloric acid (HCl) modification was applied and optimized by Box-Behnken model-based response surface methodology. After modification by HCl, the specific surface area, pore volume, and average pore diameter of modified algae-derived biochar (MAB) increased to 38.34 m2/g, 0.073 cm³ /g, and 7.42 nm, respectively. The removal efficiency of Microcystis aeruginosa (The initial cell density: 4 ×106 cells/mL) by the MAB reached 99.02%±0.18 under the optimum condition obtained with response surface experiment (dosage of 287.46 mg/L, pH of 8.2, stirring rate of 175 rpm, and stirring time of 6.4 min). At the same time, the removal efficiencies of Chl a, turbidity and total phosphorus of polluted waters reached more than 84%, 91% and 60%, respectively. The dissolved organic matters were removed synchronously, thereby reducing the disinfection by-products formation potential. Electrostatic adsorption has been determined as the predominant force during the coagulation process. In conclusion, the HCl has been proved to be an effective strategy to improve the pore structure and algal removal capacity of MAB, and the MAB could be applied as the suitable materials for the algal coagulation with the advantage of resource utilization.

NOM fractionation by HPSEC-DAD-OCD for predicting trihalomethane disinfection by-product formation potential in full-scale drinking water treatment plants

Chlorination is a common method for water disinfection; however, it leads to the formation of disinfection by-products (DBPs), which are undesirable toxic pollutants. To prevent their formation, it is crucial to understand the reactivity of natural organic matter (NOM), which is considered a dominant precursor of DBPs. We propose a novel size exclusion chromatography (SEC) approach to evaluate NOM reactivity and the formation potential of total trihalomethanes-formation potentials (tTHMs-FP) and four regulated species (i.e. CHCl3, CHBrCl2, CHBr2Cl, and CHBr3). This method combines enhanced SEC separation with two analytical columns working in tandem and quantification of apparent molecular weight (AMW) NOM fractions using C content (organic carbon detector, OCD), 254-nm spectroscopic (diode-array detector, DAD) measurements, and spectral slopes at low (S206–240) and high (S350–380) wavelengths. Links between THMs-FP and NOM fractions from high performance size exclusion chromatography HPSEC-DAD-OCD were investigated using statistical modelling with multiple linear regressions for samples taken alongside conventional full-scale as well as full- and pilot-scale electrodialysis reversal and bench-scale ion exchange resins. The proposed models revealed promising correlations between the AMW NOM fractions and the THMs-FP. Methodological changes increased fractionated signal correlations relative to bulk regressions, especially in the proposed HPSEC-DAD-OCD method. Furthermore, spectroscopic models based on fractionated signals are presented, providing a promising approach to predict THMs-FP simultaneously considering the effect of the dominant THMs precursors, NOM and Br−.

UV aging of microplastic polymers promotes their chemical transformation and byproduct formation upon chlorination

The presence and accumulation of microplastics (MPs) in water and wastewater is a growing concern. When released to the water bodies, microplastics can be subject to surface weathering due to ultraviolet (UV) exposure. In this study, the effects of UV aging of six MP polymers from three groups (e.g., polyamide, polyester, and polyolefin) on their chlorine reactivity, chemical transformation, and formation of disinfection byproducts (DBPs) were studied. Polyamide (e.g., polyamide 6) in both virgin and UV-aged forms showed significantly higher chlorine demands than other MP polymers (915.5–947.9 versus 7.0–21.1 μmol/g MP in 24 h), and polyolefins were relatively inert to chlorine. UV aging enhanced the destructions of functional groups of polyamide and polyester upon chlorination, promoting the chlorine demands and leaching of organics by up to 1.7- and 2.4-fold, respectively. Polymer monomer and oligomers of polyamide 6 and toxic or endocrine disrupting additives (e.g., dimethyl phthalate and butyl octyl phthalate) were identified in leachates from chlorinated MP polymers by mass spectrometry. Meanwhile, up to >10-fold increases in the yields of trihalomethane, haloacetic acid, haloacetaldehyde, haloacetonitrile, and haloacetamide were observed from 30-day UV-aged MP polymers as compared to their virgin counterparts. Overall, this study reveals that UV aging can promote the reactivity and chemical transformation of MP polymers during chlorination, especially for polyamide and polyester, increase the release of polymer monomers, oligomers, and additives, and aggravate the role of MP polymers as DBP precursors.

Beneficial role of pre- and post-ozonation in a low rate biofiltration-ultrafiltration process treating reclaimed water

Previous studies have shown that the combination of biological and ozone oxidation processes can achieve a greater performance in treating natural surface water than each process individually. In this work, we designed and tested an ozonation–gravity-driven up-flow slow rate (0.01 m/h) biofiltration–ozonation (O3–GUSB–O3) process for the pre-treatment of reclaimed water prior to ultrafiltration (UF), with the aim of producing high quality drinking water and a significantly reduced degree of UF fouling. Results showed that O3 coupled with GUSB can effectively remove aromatic compounds (∼ 84.8%), dissolved organic carbon (DOC, ∼ 83.4%), and biopolymers in surface water. In addition, post-ozonation greatly contributed to the reduction of the UF membrane fouling (∼ 6 times greater flux). With regard to the disinfection by-product formation potential (DBPFP) of the final treated water, both trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP) were greatly reduced (86.4% and 84.8% for THMs and HAAs, respectively). The relationship between DBPFP and various spectral indexes revealed that aromatic compounds and amino acids were more likely to generate DBPs during the disinfection stage. Among these, humic substances were more likely to generate THMs, while low molecular weight carboxylate and carbonyl organic compounds were associated with the generation of HAAs. Moreover, the dosage of O3 during the post-ozonation stage was found to influence directly the generation of DBPs. Overall, this study has conducted a detailed evaluation of a novel multi-ozone biofilter UF process for treating surface water, and the results provide a valuable basis for subsequent studies at larger scale to demonstrate the potential of the treatment process for practical applications.

A new process to further remove dissolved organic matter and disinfection by-product formation potential during drinking water treatment.

Biological activated carbon (BAC) will produce soluble microbial products (SMPs), which affect effluent quality. To clarify the mechanism by which BAC affects effluent water quality, the processes of a drinking water plant in Jiangsu Province were investigated. It was found that during the O3-BAC process, although ozonation could remove dissolved organic matter (DOC) to a certain extent, the DOC increased from 4.44 to 4.47mg/L after BAC. Dissolved organic matter (DOM) in effluent from different processes was divided into five fractions based on hydrophilicity and hydrophobicity by resin fractionation. Through fluorescence excitation-emission matrix (EEM) spectroscopy combined with DOC analysis, it was found that SMPs are mainly included in transitional hydrophilic neutral (TPIN) fraction, which was the main cause of the DOC increase. Therefore, a new combined process was designed to remove TPIN effectively by coagulation after biological treatment, and found that coagulation had a good removal rate (13.2%) on TPIN. The trihalomethane formation potential (THMFP) of TPIN could be reduced effectively by 44.9% after coagulation. Compared with the old process, the new combined process had a higher removal rate (14.2-30.0%) of DOC, as well as a greater reduction of THMFP (29.0-78.6%) and haloacetic acid formation potential (HAAFP) (46.4-75.3%). This study aims to reveal the mechanism by which SMPs affect effluent water quality and exacerbate health risks, and to propose a solution to provide theoretical support for the design and optimization of drinking water treatment processes.

Removal of algae and algogenic odor compounds via combined pre-chlorination and powdered activated carbon adsorption for source water pretreatment

This study investigated the combination sequence and time interval of chlorination and powdered activated carbon (PAC) adsorption for the control of algae inactivation, algogenic odor removal, and disinfection by-product (DBP) formation. Results indicated that pre-chlorination/post-PAC exhibited the highest algae removal efficiency in all sequential combinations of PAC adsorption and chlorination, while it had displayed slight effect on the removal of DBPs. The evaluated sequential combinations all had significant effect on the removal of odor. Nevertheless, prolonged time interval between chlorination and PAC adsorption exhibited enhanced control of algae and odor compounds in all experiments; with increasing time interval from 0 to 15 min in pre-chlorination/post-PAC process, the removal efficiency of Chl-a, algal cell viability, GSM, and 2-MIB increased by 46%, 15%, 15% and 23%, respectively. In the combined processes, the odor removal efficiency was positively correlated with PAC dosage but negatively correlated with chlorine dosage. Furthermore, PAC addition could effectively reduce the total DBP yields, especially the N-DBPs. This study can provide a better understanding of improving in-situ operation of the pre-chlorination and PAC dosing systems for source water pretreatment.

CeO2 modified carbon nanotube electrified membrane for the removal of antibiotics

Electrified carbon nanotube membranes (ECM) are used as electroactive porous materials for the degradation of micropollutants. It integrated design of both electrochemical processes and filtration functions. In this study, CeO2 modified carbon nanotube electrified membrane (CeO2@CNT membrane) was prepared and activate NaClO towards degradation of antibiotics. As CeO2 with face-centered cubic (Fcc) fluorite structure was loaded onto the CNT sidewalls, the CeO2@CNT membrane showed a higher over potential and a smaller equivalent polarization resistance compared to ECM. More reactive oxygen species (ROS) and reactive chlorine species (RCS) were generated by CeO2@CNT membrane due to faster electron transfer at the solid-liquid interface. Thus, the removal efficiencies of DCF, SMX, CIP, TC and CBZ were more than 91.2%, 91.3%, 94.4%, 99.3% and 89.4% by the CeO2@CNT membrane with NaClO, respetively. And the apparent reaction rate constant (k) of the CeO2@CNT membrane was 2.9 times of that of ECM. The selective capping experiments and density functional theory (DFT) calculation showed that the oxygen vacancies of CeO2 contributed to the generation of ‧OH, and the generation of ClO‧ and ‧O2− would mainly occur on Lewis acid sites of CeO2. In addition, the CeO2@CNT membrane showed a reasonable stability to treat actual water samples and reduced disinfection byproducts (DBPs) formation, suggesting that it can potentially be combined with the conventional chlorine disinfection to degrade antibiotics in water.

Self-Powered Water Disinfection System Acheving a Novel Oxidation-Assisted Electroporation Mechansim with Rotational Triboelectric Nanogenerator

In world, one of three people lack reliable access to clean water and water-borne diseases resulting from pathogenic microbescontaminated water remain a great threat to public health. Disinfection is an effective drinking water purification method; however, the most commonly used water disinfection method, chlorination, is limited by carcinogenic disinfection byproducts formation. Alternative methods such as ultraviolet (UV) radiation and membrane filtration suffer from drawbacks such as pathogen regrowth, low throughput, and intensive energy/chemical consumption. In addition, the methods have a limited disinfecting capacity and may be inadequate during a crisis like in cases of a severe epidemic outbreak, such as coronavirus disease 2019. Here, we report a rapid, self-powered water disinfection system for both bacterial and viral inactivation based on a novel oxidation-assisted electroporation mechanism powered by a supercoiling-mediated rotational TENG (S-TENG) that converts the periodic hand stretching/releasing into high-speed rotation. Owing to a rational design of the S-TENG that yields an ultrafast rotation (≈7500 rpm), we successfully overcame the insufficient output limitations of TENG caused by the low-frequency stimuli ambient energy harvesting. The S-TENG with sufficient voltage and current output can generate an NW-enhanced localized electric field and oxidative species simultaneously, and therefore achieving high disinfection efficiency. More than 99.9999% of bacteria and viruses were inactivated at a high flux of 15 m3 h–1 m–2. Our work presented an efficient enlarged demonstrator wherein 1 L of natural water can flow through the whole system within 1 min solely driven by gravity, and achieve complete disinfection, confirming the feasibility of this method for water disinfection in areas with an inadequate power supply. Figure 1

Change of algal organic matter under different dissolved oxygen and pressure conditions and its related disinfection by-products formation potential in metalimnetic oxygen minimum

Most of the reservoirs or lakes will form a metalimnetic oxygen minimum (MOM) with the characterization of a substantial fraction of dissolved oxygen (DO) depleted below the epilimnion. The effect of intracellular organic matter (IOM) of algal cells transformed under MOM conditions is completely different from that of the original IOM on water quality. In this study, the IOM changes of Microcystic aeruginosa under different MOM conditions and its related disinfection by-products formation potentials (DBPFPs) were investigated by changing the pressure and DO concentration of MOM. Total Fmax increased slightly and then decreased under different pressure conditions, finally decreasing by no more than 22.0%. Under aerobic condition, dissolved organic carbon (DOC) and total Fmax decreased significantly, and decreased by 60.4% and 38.8% within the first 2 days. The results of specific UV absorbance (SUVA) and UV250/UV365 indicated that aromatic compounds and average molecular weight of IOM were gradually increased under different MOM conditions. The total DBPFPs increased firstly and then decreased under different pressure conditions, and finally decreased by 26.2%-33.1%. The decrease of total DBPFPs was significantly higher under aerobic condition than that under anoxic condition, which finally decreased by 64.5%. Redundancy analysis showed that the fluorescence parameter (protein-like and humic-like fluorescence) could be expected as an index to predict the DBPFPs. Moreover, the results revealed that with the decrease of DO, the activity and diversity of natural microbial consortium decreased, which prevented the further degradation and utilization of organic matter by natural microbial consortium. Therefore, lower DO was a key player for the deterioration of water quality under MOM conditions.