Dihalogenated nitrophenols in drinking water: Prevalence, resistance to household treatment, and cardiotoxic impact on zebrafish embryo.

Dihalogenated nitrophenols (2,6-DHNPs), an emerging group of aromatic disinfection byproducts (DBPs) detected in drinking water, have limited available information regarding their persistence and toxicological risks. The present study found that 2,6-DHNPs are resistant to major drinking water treatment processes (sedimentation and filtration) and households methods (boiling, filtration, microwave irradiation, and ultrasonic cleaning). To further assess their health risks, we conducted a series of toxicology studies using zebrafish embryos as the model organism. Our findings reveal that these emerging 2,6-DHNPs showed lethal toxicity 248 times greater than that of the regulated DBP, dichloroacetic acid. Specifically, at sublethal concentrations, exposure to 2,6-DHNPs generated reactive oxygen species (ROS), caused apoptosis, inhibited cardiac looping, and induced cardiac failure in zebrafish. Remarkably, the use of a ROS scavenger, N-acetyl-l-cysteine, considerably mitigated these adverse effects, emphasizing the essential role of ROS in 2,6-DHNP-induced cardiotoxicity. Our findings highlight the cardiotoxic potential of 2,6-DHNPs in drinking water even at low concentrations of 19 µg/L and the beneficial effect of N-acetyl-l-cysteine in alleviating the 2,6-DHNP-induced cardiotoxicity. This study underscores the urgent need for increased scrutiny of these emerging compounds in public health discussions.

Dihalogenated nitrophenols exposure induces developmental neurotoxicity in zebrafish embryo.

2,6-Dihalogenated nitrophenols (2,6-DHNPs) are emerging halogenated nitroaromatic pollutants that have been detected in various water environments. However, there is currently limited research available regarding their potential impacts on locomotion behavior and neurotoxicity. Therefore, this study utilized zebrafish embryos to investigate the potential neurotoxic effects of 2,6-DHNPs by examining their impact on the nervous system at a concentration defined as 10% of the median lethal concentration. Our findings demonstrated that exposure to 2,6-DHNPs resulted in a significant 30 % decrease in the total swimming distance of zebrafish larvae, accompanied by notable impairments in motor neuron development and central nervous system. These effects were evidenced by a substantial 25% decrease in axonal growth, as well as disruptions in synapse formation and neuronal differentiation. Additionally, neurotransmitter analysis revealed marked decreases of 40%, 35%, and 30% in dopamine, 5-hydroxytryptamine, and acetylcholine levels respectively, highlighting disturbances in their synthesis, transport, and degradation mechanisms. These results emphasize the considerable neurotoxicity of 2,6-DHNPs at concentrations previously considered safe; thus necessitating a re-evaluation of environmental risk assessments and regulatory standards for such emerging contaminants.

Emerging disinfection byproducts 3-bromine carbazole induces cardiac developmental toxicity via aryl hydrocarbon receptor activation in zebrafish larvae.

3-bromine carbazole (3-BCZ) represents a group of emerging aromatic disinfection byproducts (DBP) detected in drinking water; however, limited information is available regarding its potential cardiotoxicity. To assess its impacts, zebrafish embryos were exposed to 0, 0.06, 0.14, 0.29, 0.58, 1.44 or 2.88 mg/L of 3-BCZ for 120 h post fertilization (hpf). Our results revealed that ≥1.44 mg/L 3-BCZ exposure induced a higher incidence of heart malformation and an elevated pericardial area in zebrafish larvae; it also decreased the number of cardiac muscle cells and thins the walls of the ventricle and atrium while increasing cardiac output and impeding cardiac looping. Furthermore, 3-BCZ exposure also exhibited significant effects on the transcriptional levels of genes related to both cardiac development (nkx2.5, vmhc, gata4, tbx5, tbx2b, bmp4, bmp10, and bmp2b) and cardiac function (cacna1ab, cacna1da, atp2a1l, atp1b2b, atp1a3b, and tnnc1a). Notably, N-acetyl-L-cysteine, a reactive oxygen species scavenger, may alleviate the failure of cardiac looping induced by 3-BCZ but not the associated cardiac dysfunction or malformation; conversely, the aryl hydrocarbon receptor agonist CH131229 can completely eliminate the cardiotoxicity caused by 3-BCZ. This study provides new evidence for potential risks associated with ingesting 3-BCZ as well as revealing underlying mechanisms responsible for its cardiotoxic effects on zebrafish embryos.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics.

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5 mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

The combination of multiple linear regression and adaptive neuro-fuzzy inference system can accurately predict trihalomethane levels in tap water with fewer water quality parameters.

Artificial Neural Network (ANN) models are accurate in predicting the levels of disinfection by-products (DBPs) in drinking water. However, these models are not yet practical due to the large number of parameters involved, which should take a significant amount of time and cost to detect. Developing accurate and reliable prediction models of DBPs with fewest parameters is essential in the management of drinking water safety. This study used the adaptive neuro-fuzzy inference system (ANFIS) and radial basis function artificial neural network (RBF-ANN) to predict the levels of trihalomethanes (THMs), the most abundant DBPs in drinking water. Two water quality parameters identified by multiple linear regression (MLR) models were used as model inputs, and the quality of the models was assessed based on criteria such as correlation coefficient (r), mean absolute relative error (MARE), and the percentage of predictions with absolute relative error less than 25% (NE<25%) and over than 40% (NE>40%), etc. The results showed that the ANFIS models had higher correlation coefficients (r = 0.853-0.898) and prediction accuracy (NE<25% = 91%-94%) compared to RBF-ANN models (r = 0.553-0.819; NE<25% = 77%-86%) and traditional MLR models (r = 0.389-0.619; NE<25% = 67%-77%). Conversely, the prediction error, as indicated by MARE and NE>40%, showed the opposite trend: ANFIS models (MARE = 8%-11%; NE>40% = 0-5%) < RBF-ANN models (MARE = 15%-18%; NE>40% = 5%-11%) < MLR models (MARE = 19%-21%; NE>40% = 11%-17%). The present study provided a novel approach for constructing high-quality prediction models of THMs in water supply systems using only two parameters. This method holds promise as a viable alternative for monitoring THMs concentrations in tap water, thereby contributing to the improvement of water quality management strategies.

Cytotoxicity of nitrogenous disinfection byproducts: A combined experimental and computational study.

Nitrogenous disinfection byproducts (N-DBPs), such as halocetamides (HAcAms), haloacetonitriles (HANs) and halonitromethanes (HNMs), are emerging DBPs in drinking water. They are more toxic than currently regulated DBPs, attracting more attention to their toxic effects and mechanism. In this study, human embryonic kidney (HEK) 293T cells were employed to explore the cytotoxicity of 29 N-DBPs. The influence of molecular structures and different halogenations on cytotoxicity has been comparatively analyzed. As toxicity is the downstream of chemico-biological interactions, the thiol reactivity of 29 N-DBPs has thus been evaluated by using glutathione (GSH) as a model nucleophile, which is the most prevalent cellular thiol and acts as an antioxidant to protect cells by detoxifying electrophilic compounds. Results show that the cytotoxicity of N-DBPs follows by the order of HAcAms > HANs > HNMs, which is different from their reactivity with GSH (the median of kGSH ranks as HNMs > HAcAms > HANs). However, a significant correlation (p < 0.001) between log kGSH and log IC50 (concentration causing 50% inhibition) has been respectively observed for HAcAms and HANs subset and HNMs subset, indicating such chemical reaction is a probable trigger for these DBPs to result in cytotoxicity. Finally, two separate quantitative structure - activity relationship (QSAR) models based on HANs & HAcAms subset and HNMs subset have been developed for estimating IC50 values. The good statistical performance makes the models possible to quickly and accurately predict IC50 values of other N-DBPs, providing basic data for their health risk assessment and greatly reducing in vivo and in vitro experiments.

Molecular insights of 2,6-dichlorobenzoquinone-induced cytotoxicity in zebrafish embryo: Activation of ROS-mediated cell cycle arrest and apoptosis.

2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), as an emerging disinfection by-product, has been frequently detected in waters, posing potential health risk on public health. Although some studies have pointed out that 2,6-DCBQ exposure can induce cytotoxicity, limited information is available for underlying mechanism for 2,6-DCBQ-induced cytotoxicity. To explore this mechanism, we assessed the levels of reactive oxygen species (ROS), acridine orange (AO) staining, and the mRNA transcriptions of genes (Chk2, Cdk2, Ccna, Ccnb and Ccne) involved in cell-cycle and genes (p53, bax, bcl-2 and caspase 3) involved in apoptosis in zebrafish embryo, after exposed to different concentrations (10, 30, 60, 90 and 120 µg/L) of 2,6-DCBQ for 72 h. Our results indicated that 2,6-DCBQ exposure induced ROS generation and cell apoptosis, and disturbed the mRNA transcription of genes related to cell cycle and apoptosis in zebrafish embryo. Moreover, we also found that 30 ~ 60 µg/L 2,6-DCBQ is the important transition from cell-cycle arrest to cell apoptosis. These results provided novel insight into 2,6-DCBQ-induced cytotoxicity.

High propensity of membrane fouling and the underlying mechanisms in a membrane bioreactor during occurrence of sludge bulking.

While sludge bulking often occurring in activated sludge processes generally leads to serious membrane fouling in membrane bioreactors (MBR), the underlying causes are still unclear. In this study, fouling behaviors of a MBR operated at stages of normal and sludge bulking were compared, and the fouling mechanisms of the different behaviors were explored. It was found that, the MBR could be stably operated in normal stage without membrane cleaning for about 60 days, whereas, daily membrane cleaning had to be carried out when operated in sludge bulking stage. The bulking sludge possessed a rather high specific filtration resistance (SFR) of about 1.36×1014 m·kg-1, which is over 5.33 times than that of the normal sludge. A series of characterizations demonstrated that the bulking sludge had rather lower dewaterability, smaller particle size, higher fractal dimension, higher viscosity, abundant filamentous bacteria and different functional groups of extracellular polymer sustains (EPS). It was suggested that microbial community transition was responsible for the occurrence of sludge bulking, further affecting membrane fouling. Based on these characterizations, it was reported that adhesion propensity (indicated by the thermodynamic interaction) of the bulking sludge to the membrane surface is about 3.6 times than that of the normal sludge. It was proposed that, extra force should be provided to offset a chemical potential gap caused by foulant layer structure transition during sludge bulking in order to sustain filtration of the bulking sludge, resulting in extremely high SFR. This study offered deep thermodynamic mechanisms of MBR fouling during occurrence of sludge bulking.

Oxidative Stress Responses and Gene Transcription of Mice under Chronic-Exposure to 2,6-Dichlorobenzoquinone.

2,6-Dichlorobenzoquinone (2,6-DCBQ), as an emerging disinfection by-production, was frequently detected and identified in the drinking water; however, limited information is available for the toxic effect of 2,6-DCBQ on mice. In the present study, adult mice were used to assess the impact of 2,6-DCBQ via measuring the responses of antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)), the key genes (Heme oxygenase-1 (HO-1), NADPH quinone oxidoreductase 1 (NQO1) and glutamate-L-cysteine ligase catalytic subunit (GCLC)) in the Nrf2-keap1 pathway, and lipid peroxidation (malonaldehyde, MDA). Our results clearly indicated that 2,6-DCBQ decreased the activities of SOD and CAT, repressed the transcriptional levels of key genes in Nrf2-keap1 pathway, further caused oxidative damage on mice. These results provided evidence for assessing the threat of 2,6-DCBQ on human.

Molecular-level insights into the mitigation of magnesium-natural organic matter induced ultrafiltration membrane fouling by high-dose calcium based on DFT calculation.

While magnesium cation (Mg2+) universally coexists with natural organic matter (NOM) in the water environment, influence of Mg2+ on NOM fouling in membrane filtration process is still unclear. This work was therefore performed to investigate effects of Mg2+ on NOM (sodium alginate (SA) as a model substance) fouling and role of Ca2+ in mitigating fouling from Mg2+ in the ultrafiltration (UF) water treatment process. Filtration tests showed two interesting fouling phenomena: (1) membrane fouling caused by combination of Mg2+ and SA maintained at a high value with the increased Mg2+ concentration; (2) the high fouling property of Mg2+ can be significantly improved by the prominent addition of calcium cation (Ca2+). It was found that changes of foulant morphology played essential roles through thermodynamic mechanisms represented by the Flory-Huggins lattice theory. Density functional theory (DFT) calculation showed that the combination of SA and Mg2+ tends to coordinate two terminal carboxyl groups in SA, beneficial to stretching alginate chains and forming a stable gel network at low doses. In addition, intramolecular coordination is difficult to occur between SA and Mg2+ due to the high hydration repulsion radius of Mg2+. Therefore, a dense and thick gel network remained even under high Mg2+concentration. Furthermore, due to the higher binding affinity of Ca2+ over Mg2+, high doses of Ca2+ trigger a transition of the stable SA-Mg2+ gel network to other configurations where flocculation and aggregation occur, thereby reducing the specific filtration resistance. The proposed thermodynamic mechanism satisfactorily explained the above interesting fouling behaviors, facilitating to development of new solutions to control membrane fouling.

Molecular insights into membrane fouling caused by polysaccharides with different structures in polyaluminum chloride coagulation-ultrafiltration process.

In this study, mechanisms of membrane fouling caused by polysaccharides with different molecular structures in polyaluminum chloride (PACl) coagulation-ultrafiltration (C-UF) process were explored. Carrageenan and xanthan gum were chosen for model foulants of straight chain and branched chain polysaccharides, respectively. Filtration experiments showed that, with PACl dosage of 0-5 mM, specific filtration resistance (SFR) of carrageenan and xanthan solution showed a unimodal pattern and a continuous decrease pattern, respectively. A series of experimental characterizations indicated that the different SFR pattern was closely related to structure of foulants layer. Density functional theory (DFT) calculation suggested that Al3+ preferentially coordinating with the terminal sulfonyl groups of carrageenan chains to promote gel layer formation at low PACl concentration (0.15 mM). There existed a chemical potential gap between bound water in gel layer and free water in the permeate, so that, filtration through gel layer corresponded to rather high SFR for overcoming this gap. In contrast, Al3+ coordinating with the non-terminal sulfonyl groups of carrageenan at high PACl concentration caused transition from gel layer to cake layer, leading to SFR decrease. However, xanthan gum itself can form a dense gel layer with a complex polymer network by virtue of the interlacing of main chains and branches. Al3+ coordinating with the carboxyl groups on branched chains of xanthan gum resulted in clusters of polymer chains and flocculation, corresponding to the reduced SFR. This proposed molecular-level mechanism well explained membrane fouling behaviors of polysaccharides with different molecular structure, and also facilitated to optimize C-UF process for water treatment.

Pilot Study of Pollution Characteristics and Ecological Risk of Disinfection Byproducts in Natural Waters in Hong Kong.

Increased disinfection efforts in various parts of China, including Hong Kong, to prevent the spread of the novel coronavirus may lead to elevated concentrations of disinfectants in domestic sewage and surface runoff in Hong Kong, generating large quantities of toxic disinfection byproducts. Our study investigated the presence and distribution of four trihalomethanes (THMs), six haloacetic acids (HAAs), and eight nitrosamines (NAMs) in rivers and seawater in Hong Kong. The concentrations of THMs (mean concentration: 1.6 µg/L [seawater], 3.0 µg/L [river water]), HAAs (mean concentration: 1.4 µg/L [seawater], 1.9 µg/L [river water]), and NAMs (mean concentration: 4.4 ng/L [seawater], 5.6 ng/L [river water]) did not significantly differ between river water and seawater. The total disinfection byproduct content in river water in Hong Kong was similar to that in Wuhan and Beijing (People's Republic of China), and the total THM concentration in seawater was significantly higher than that before the COVID-19 pandemic. Among the regulated disinfection byproducts, none of the surface water samples exceeded the maximum index values for THM4 (80 µg/L), HAA5 (60 µg/L), and nitrosodimethylamine (100 ng/L) in drinking water. Among the disinfection byproducts detected, bromoform in rivers and seawater poses the highest risk to aquatic organisms, which warrants attention and mitigation efforts. Environ Toxicol Chem 2022;41:2613-2621. © 2022 SETAC.

Occurrence and distribution of antibiotics in surface water.

The concentrations, distribution, and ecological risks of 24 typical antibiotics in Hong Kong rivers and seawater were investigated using high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UHPLC-EI-MS/MS). The results showed that the select antibiotics were widely distributed in the study area. Among the target antibiotics, the detection rate of tetracyclines (TCs) was 100%, which indicated the widespread use of TCs in Hong Kong. The detection rates of sulfonamides (SAs) (57.1-100%), fluoroquinolones (FQs) (78.6-100%), roxithromycin (RTM) (50%) and novobiocin (NOV) (50%) were all above 50%. Compared with river water (7.9-114.26 ng/L, medium: 27.7 ng/L), concentrations of the most antibiotics in seawater (9.5-32.0 ng/L, medium: 13.3 ng/L) were lower; seawater concentrations were similar to those reported from other coastal cities, such as Guangzhou and Zhuhai in China, which implied that the source of marine antibiotic pollution may be the nearby rivers, and the vastness of the ocean causes environmental dilution of antibiotics. According to the ratio of the measured environmental concentration (MEC) to the predicted no-effect concentration (PNEC), ofloxacin (OFX) (average risk quotient: 1.94E-01) and ciprofloxacin (CFX) (average risk quotient: 3.53E-01) posed medium to high ecological risk in most places, whereas other antibiotics posed lower risk. In Yuen Long, where there were many livestock farms nearby, the detected concentration of antibiotics was higher, indicating that livestock wastewater may be the major reason for the increase in antibiotic levels in this area. In general, the detected concentration of antibiotics in Hong Kong was lower than that in the United States, Japan, the United Kingdom, and coastal areas of China, but the long-term existence of low concentrations of antibiotics also poses great risks. According to the risk assessment, Hong Kong should pay more attention to the use of FQs (e.g., OFX and CFX) in the future.

Effects of polysaccharides' molecular structure on membrane fouling and the related mechanisms.

Fouling behaviors of polysaccharides vary with their structure, while the mechanisms underlying this phenomenon remain unexplored. This work was carried out to explore the thermodynamic fouling mechanisms of polysaccharides with different structure. Carrageenan and xanthan gum were selected as the model polysaccharides with structure of straight and branch chains, respectively. Batch filtration experiments showed that xanthan gum solution corresponded to a more rapid flux decline trend, and specific filtration resistance (SFR) of xanthan gum (2.32 × 1015 m-1 kg-1) was over 10 times than that of carrageenan (2.21 × 1014 m-1 kg-1). It was found that, xanthan gum possessed a more disordered structure and a rather higher viscosity (15.03 mPa·s V.S. 1.98 mPa·s for carrageenan). Calculation of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed higher adhesion energy of xanthan gum (-42.82 my m-2 V.S. -23.26 mJ m-2 for carrageenan). Scanning electron microscopy (SEM) analyses showed that xanthan gum gel layer had a more homogenous structure and rigid polymer backbone, indicating better mixing with water to form a gel. As verified by heating experiments, such a structure tended to contain more bound water. According to this information, Flory-Huggins lattice theory was introduced to build a bridge between polymeric structure and SFR. It was revealed that branch structure corresponded to higher chemical potential change during gel layer formation, and higher ability to carry bound water, resulting in higher filtration resistance during filtration process. This work revealed the fundamental thermodynamic mechanism of membrane fouling caused by polysaccharides with different structure, deepening understanding of membrane fouling.

Precursor characteristics of mono-HAAs during chlorination and cytotoxicity of mono-HAAs on HEK-293T cells.

Monohaloacetic acids (mono-HAAs), a class of disinfection by-products widely occurred in drinking water, receives significant attention due to their extremely high toxicity. Many studies on the biological toxicity of mono-HAAs have been reported, yet the toxic effects of mono-HAAs on human renal cells (kidney is one of the target organs for disinfection by-products) has not been involved. Studies on organic precursors for mono-HAAs formation were also very limited due to their lower levels as compared to di-HAAs and tri-HAAs. Based on this, the formation of mono-HAAs after chlorination of some typical source water samples and their relationship with water quality parameters were investigated. Meanwhile, the cytotoxicity of monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), and monoiodoacetic acid (MIAA) were tested using human embryonic kidney cells (HEK-293 T cells). The results showed that the levels of mono-HAAs formed during chlorination of source water samples were between 0.44 and 0.87 µg/L. Formation of MBAA positively (p < 0.05) correlated with bromide ion and dissolved organic carbon, but negatively (p < 0.01) correlated with SUVA254 (specific UV absorbance at 254 nm), while formation of MCAA was only positively (p < 0.05) related with SUVA254. These results suggested that although MCAA and MBAA both belong to the mono-HAAs, the characteristics of their organic precursors differ significantly. MCAA precursors have high aromaticity and are more hydrophobic, yet MBAA precursors have low aromaticity and are more hydrophilic. The half-lethal concentrations (LC50) of MCAA, MBAA, and MIAA on HEK293T cells were 1196-1211 µM, 16.07-18.96 µM, and 6.08-6.17 µM, respectively. An in-depth analysis showed that the cytotoxicity of mono-HAAs on HEK 293 T cells could not be explained by the parameters concerning cellular uptake (e.g., logP and pKa), but the SN2 reaction of C-X bond with cellular molecules (e.g., glyceraldehyde-3-phosphate dehydrogenase, etc) may be the relevant cause for the cytotoxicity of mono-HAAs on HEK 293 T cells.

Preparation of Ni@UiO-66 incorporated polyethersulfone (PES) membrane by magnetic field assisted strategy to improve permeability and photocatalytic self-cleaning ability.

Metal-organic frameworks (MOFs) have been considered as promising nanofillers to fabricate mixed matrix membranes for water treatment. However, manipulating distribution of MOFs nanoparticles in the membrane matrix remains a great challenge. In this study, UiO-66 was firstly coated by magnetic Ni via an in-situ reduction reaction, and then incorporated into polyethersulfone (PES) membrane matrix to prepare PES-Ni@UiO-66 membrane. The magnetic Ni allowed to manipulate the distribution of magnetic Ni@UiO-66 in the phase-inversion process by an external magnetic field. The hydrophilic Ni@UiO-66 can be pulled onto membrane surface by the magnetic force, endowing the prepared membrane with rather higher hydrophilicity. The prepared membrane exhibited superior water permeability with a pure water flux of 611.5 ± 19.8 L·m-2·h-1 and improved antifouling performance. Moreover, benifiting from photocatalytic activity of the exposed Ni@UiO-66 on membrane surface, the obtained PES-Ni@UiO-66 membrane demonstrated excellent photocatalytic self-cleaning ability with a flux recovery rate (FRR) higher than 95% under UV irradiation. Analyzing by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory indicated that the improved antifouling performance could be attributed to less attractive or even repulsive interaction between the prepared membrane and pollutants. This work provided valuable guidance for structural regulation and development of high-performance MOFs-based membranes for water treatment.

Fundamental thermodynamic mechanisms of membrane fouling caused by transparent exopolymer particles (TEP) in water treatment.

While transparent exopolymer particles (TEP) has high fouling potential, its underlying fouling mechanisms have not yet been well revealed. In current work, fouling characteristics of TEP under different Ca2+ concentrations (0 to 1.5 mM) were investigated. TEP quantification and filtration tests showed that TEP contents increased with Ca2+ concentration, while TEP's specific filtration resistance (SFR) under the influence of Ca2+ concentration presented a unimodal pattern. The peak of TEP's SFR reached at Ca2+ concentration of 1 mM when SA concentration was 0.3 g·L-1. A series of characterizations suggested that microstructure transformation of TEP particles was the main contributor to the resistance variations of TEP solution. The optical microscope observation showed that above and below the critical Ca2+ concentration (1 mM when SA concentration is 0.3 g·L-1 in this study), the formed TEP existed in the form of c-TEP (average particle size is 0.24 µm) and p-TEP (average particle size is 1.05 µm), respectively. Thermodynamic analysis showed that the adhesion ability of c-TEP (-249,989 and - 303,692 kT) was more than 19 times than that of p-TEP (-12,905 kT), which would accelerate foulant layer formation. In addition, below the critical value, the increased SFR with Ca2+ concentration could be explained by integrating Flory-Huggins lattice theory with the preferential intermolecular coordination. Above the critical value, the decreased SFR can be attributed to the formation of a "large-size crack structure" cake layer from the p-TEP. This study revealed fundamental mechanisms of membrane fouling caused by TEP, greatly deepening understanding of TEP fouling, and facilitating to development of effective fouling control strategies.

A novel composite membrane for simultaneous separation and catalytic degradation of oil/water emulsion with high performance.

It is of great significance to develop novel membranes with dual-function of simultaneously separating oil/water emulsion and degrading the contained water-miscible toxic organic components. To meet this requirement, a dual-functional Ni nanoparticles (NPs)@Ag/C-carbon nanotubes (CNTs) composite membrane was fabricated via electroless nickel plating strategy in this study. The as-prepared composite membrane possessed superhydrophilicity with water contact angle of 0° and splendid underwater oleophobic property with oil contact angle of 142°. When the membrane was applied for separation of surfactant stabilized oil-in-water emulsion, high permeate flux (about 97 L m-2·h-1 under gravity), oil rejection (about 98.8%) and antifouling property were achieved. Benefitting from the NiNPs@Ag/C-CNTs layer on membrane surface, the composite membrane exhibited high catalytic degradation activity for water-miscible toxic organic pollutant (4-nitrophenol) with addition of NaBH4 in a flow-through mode. Meanwhile, the NiNPs@Ag/C-CNTs composite membrane possessed excellent durability, which was verified by the good structural integrity even under ultrasonic treatment. The cost-efficiency, high separation and degradation performance of the prepared membrane suggested its great potential for treatment of oily wastewater.

Using simple and easy water quality parameters to predict trihalomethane occurrence in tap water.

Monitoring of disinfection by-products (DBPs) in water supply system is important to ensure safety of drinking water. Yet it is a laborious job. Developing predictive DBPs models using simple and easy parameters is a promising way. Yet current models could not be well applied into practice because of the improper dataset (e.g. not from real tap water) they used or involving the parameters that are difficult to measure or require expensive instruments. In this study, four simple and easy water quality parameters (temperature, pH, UVA254 and Cl2) were used to predict trihalomethane (THMs) occurrence in tap water. Linear/log linear regression models (LRM) and radial basis function artificial neural network (RBF ANN) were adopted to develop the THMs models. 64 observations from tap water samples were used to develop and test models. Results showed that only one or two parameters entered LRMs, and their prediction ability was very limited (testing datasets: N25 = 46-69%, rp = 0.334-0.459). Different from LRM, the prediction accuracy of RBF ANNs developed with pH, temperature, UVA254 and Cl2 can be improved continuously by tweaking the maximum number of neuron (MN) and Gaussian function spread (S) until it reached best. The optimum RBF ANNs of T-THMs, TCM and BDCM were obtained when setting MN = 20, S = 100, 100.1 and 60, respectively, where the N25 and rp values for testing datasets reached 85-92% and 0.813-0.886, respectively. Accurate predictions of THMs by RBF ANNs with these four simple and easy parameters paved an economic and convenient way for THMs monitoring in real water supply system.

Environmentally relevant concentrations of arsenic induces apoptosis in the early life stage of zebrafish.

Arsenic (As) in the aquatic environment is a considerable environmental issue, previous studies have reported the toxic effects of low concentrations (≤ 150 µg/L) of As on fish. However, limited information is available regarding the impact of low levels of As on apoptosis. To evaluate this, zebrafish embryos were exposed to different concentrations (0, 25, 50, 75, and 150 µg/L) of As (arsenite [AsIII] and arsenate [AsV]) for 120 h. Our results indicated that low concentrations of AsIII exposure significantly inhibited the survival of zebrafish larvae, and significantly increased the transcription of Caspase-9 and Caspase-3, the ratio of Bax/Bcl-2 transcription, and protein levels of Caspase-3. In contrast, AsV decreased the ratios of Bax/Bcl-2 transcription and protein levels, as well as protein levels of Caspase-3. Our data demonstrated that AsIII and AsV exert different toxic effects, AsIII induced apoptosis via the mitochondrial pathway and the extrinsic pathway, while AsV induced apoptosis only via the mitochondrial pathway.