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In view of the high risks brought about by organic micropollutants (OMPs), nanofiltration (NF) processes have been playing a vital role in advanced water and wastewater treatment, owing to the high membrane performance in rejection of OMPs, permeation of water, and passage of mineral salts. Though numerous studies have been devoted to evaluating and technically enhancing membrane performance in removing various OMPs, the trade-off effect between water permeance and water/OMP selectivity for state-of-the-art membranes remains far from being understood. Knowledge of this effect is significant for comparing and guiding membrane development works toward cost-efficient OMP removal. In this work, we comprehensively assessed the performance of 88 NF membranes, commercialized or newly developed, based on their water permeance and OMP rejection data published in the literature. The effectiveness and underlying mechanisms of various modification methods in tailoring properties and in turn performance of the mainstream polyamide (PA) thin-film composite (TFC) membranes were quantitatively analyzed. The trade-off effect was demonstrated by the abundant data from both experimental measurements and machine learning-based prediction. On this basis, the advancement of novel membranes was benchmarked by the performance upper-bound revealed by commercial membranes and lab-made PA membranes. We also assessed the potentials of current NF membranes in selectively separating OMPs from inorganic salts and identified the future research perspectives to achieve further enhancement in OMP removal and salt/OMP selectivity of NF membranes.

Ozone has been widely applied in drinking water and wastewater treatment plants, and it is essential to determine the ozone dosage and its ratio in ozone contact tank to increase the ozone absorption and utilization rates. Batch experiments were performed to determine the first-order reaction rate coefficient of ozone (k1) in different raw water qualities. Results showed that k1 had an exponential decaying relationship with the ozone consumption amount (ΔO3). Based on the ozone mass transfer and decomposition kinetics, a numerical model was developed to optimize the total ozone dosage and its ratio in three aeration parts by calculating the ozone absorption and utilization rates in an ozone contact tank. The ozone absorption rate was little affected by the water quality, and an even distribution of ozone could greatly increase the ozone absorption rate. However, the ozone utilization rate was tightly related with the water quality. For waters that consumed ozone quickly, ozone should be dosed equally in three aeration parts to increase the ozone utilization rate up to 94.3%. Otherwise, more ozone should be dosed in the first aeration part. An increase in ozone utilization rate would induce an increase in the degree of water purification. This model could give theoretical support for the determination of ozone dosage and its ratio in water treatment plants rather than experience.

Water and wastewater infrastructure worldwide faces unprecedented demand and supply conflicts that require unconventional solutions. In this study, we develop a novel modelling framework to assess the environmental and economic implications of a hybrid water supply system that supplements a centralized surface water supply with distributed direct potable reuse (DPR) of municipal wastewater, as a strategy to address such challenges. The model is tested with real water and wastewater systems data from the City of Houston, Texas. Results show that supplementing the conventional centralized water supply with distributed DPR would reduce water age in the drinking-water distribution network and hence improve water quality; properly designed system configurations attain system-wide net energy savings even with the high energy consumption of existing technologies used for advanced treatment of the wastewater. A target energy efficiency for future advanced treatment technologies is identified to achieve net energy saving with all hybrid system configurations. Furthermore, distributed DPR remains financially competitive compared with other unconventional water supply solutions. The modelling framework and associated databases developed in this study serve an important research need for quantitatively characterizing distributed and hybrid water systems, laying the necessary foundation for rational design of integrated urban water systems. Water and wastewater infrastructure worldwide faces unprecedented challenges. A new model can assess the environmental and economic implications of a hybrid water supply system that provides a centralized surface water supply with distributed direct potable reuse of municipal wastewater.

Conventional dense thin-film composite (TFC) membranes evince a universally low water permeability, the increase of which typically relies on introducing additional transport channels based on intricate steps within a membrane preparation process. In this study, we reported a novel and simplified procedure for the fabrication of high-performance TFC membranes. Specifically, the dissolution of aqueous monomers in the casting solution was utilized for the following interfacial polymerization (IP). Since the monomers diffused to the water bath during phase inversion, the control of precipitation time enabled an effective regulation of the monomer concentration in the formed polymeric substrates, where the IP reaction was initiated by the addition of the organic phase. The entire and uniform embedment of aqueous monomers inside the substrates contributed to the formation of ultrathin and smooth selective layers. An excellent separation performance (i.e., water permeability: 34.7 L m-2 h-1 bar-1; Na2SO4 rejection: ∼96%) could be attained using two types of aqueous monomers (i.e., piperazine and β-cyclodextrin), demonstrating the effectiveness and universality of this method. Compared to the conventional immersion-based process, this novel procedure shows distinct advantages in reducing monomer usage, shortening the production cycle, and achieving a more superior membrane performance, which is highly promising for large-scale membrane manufacture.

Isoprothiolane (IPT) was one of the most commonly used pesticides around the world. It was reported to be the highest concentration and frequency of detection of 13 most commonly used pesticides in Mekong Delta recently. The oxidation degradation kinetic of ozone and chlorine with IPT and the identification of the degradation products was investigated in this research. The results showed that both ozone and chlorine oxidized IPT rapidly under typical water treatment condition, and that both reactions followed second order reaction kinetics. The ozone reaction rates exhibited no pH dependence with the rate constant of 247.1 (±11.0) M−1s−1 at 25 °C, whereas chlorine reaction rates increased dramatically with decreasing pH. The rate constant for hypochloric acid was 73.3 (±3.1) M−1s−1 at 25 °C, while the reaction of hypochlorite was negligible. The degradation products by chlorine and ozone were identified by LC-MS/MS and the reaction pathways were proposed. The thioether and the carbon-carbon double bond in IPT were the reactive sites during chlorine and ozone oxidation. The thioether group was oxidized into sulfoxide and further sulfone group, and the carbon-carbon double bone were cleaved to form diisopropyl ester of malonic acid, diisopropyl ester of tartronic acid and diisopropyl ester of ketomalonic acid monohydrate. Compared to ozone reaction, it was more complicated for chlorine reaction, which yielded chlorine substituted, hydroxylated and dithiolane ring-opening products.

Nanofiltration (NF) is considered as a promising technology for the removal of trace organic compounds (TrOCs) for wastewater reclamation, while a simultaneous low rejection of salts is desirable for the ease of using the reclaimed water. This study was conducted to exploit the potential of polypiperazine-amide NF membranes in achieving selective separation of TrOCs and NaCl by varying the concentration of the diamine monomer, piperazine (PIP), for interfacial polymerization and by modifying the nascent membrane surface with hydrophilic monomers, diethanolamine (DEA) and monoethanolamine (MEA). Results showed that increasing PIP concentration could decrease the membrane pore size and reduce the surface negative charge density, which led to an increased rejection of xylose and a reduced rejection of NaCl. The grafting of DEA or MEA molecules could further decrease the NaCl rejection, substantially improve the water permeability and maintain an effective removal for eight pharmaceuticals (PhACs). The optimal membrane prepared with a PIP concentration of 2.0 wt% and subsequently modified by MEA exhibited a rejection of NaCl at 33.1% and an average rejection of PhACs at 90.8% in a 10 mmol/L NaCl solution under an applied pressure of 6 bar. The membrane could have an even higher selectivity when the NaCl concentration was increased to higher levels. These results demonstrated the feasibility and versatility of the membrane in separating TrOCs from NaCl for wastewater reclamation.

Colloids and organics in shale gas fracturing flowback water (SGFFW) during shale gas extraction are of primary concerns. Coagulation combined with oxidation might be a promising process for SGFFW treatment. In this study, a novel electrocoagulation-peroxone (ECP) process was developed for SGFFW treatment by simultaneous coagulation and oxidation process with a Al plate as the anode and a carbon-PTFE gas diffusion electrode as the cathode, realizing the simultaneous processes of coagulation, H2O2 generation and activation by O3 at the cathode. Compared with electrocoagulation (EC) and peroxi-electrocoagulation (PEC), COD removal efficiency mainly followed the declining order of ECP, PEC and EC under the optimal current density of 50 mA cm−2. The appearance of medium MW fraction (1919 Da) during ozonation and PEC but disappearance in ECP indicated that these intermediate products couldn't be degraded by ozonation and PEC but could be further oxidized and mineralized by the hydroxyl radical produced by the cathode in ECP, demonstrating the hydroxyl radical might be responsible for the significant enhancement of COD removal. The pseudo-first order kinetic model can well fit ozonation and EC process but not the PEC and ECP process due to the synthetic effect of coagulation and oxidation. However, the proposed mechanism based model can generally fit ECP satisfactorily. The average current efficiency for PEC was 35.4% and 12% higher than that of ozonation and EC, respectively. This study demonstrated the feasibility of establishing a high efficiency and space-saving electrochemical system with integrated anodic coagulation and cathodic electro-peroxone for SGFFW treatment.

A simultaneous high rejection of trace organic compounds (TrOCs) and low rejection of divalent cations (Ca2+/Mg2+) would be desirable for nanofiltration (NF) applied for drinking water treatment. The target was however not attainable by using the currently available commercial NF membranes. In this study, 3,5-diaminobenzoic acid (BA) was used as an additional diamine monomer besides piperazine (PIP) to prepare novel thin film composite NF membranes via interfacial polymerization with trimesoyl chloride (TMC). A series of NF membranes were prepared by varying BA to PIP concentration ratios in order to obtain a proper membrane pore size and a sufficiently high negative surface charge density. Membrane characterizations and performance tests showed that the incorporation of BA could increase the pore size, enhance the negative surface charge and change the structural properties of the membrane, which in turn affected the membrane water permeability and separation performance. The optimal membrane prepared with a BA/PIP ratio of 50%:50% exhibited a low rejection of CaCl2 (25.8%) and MgCl2 (32.0%) in single salt solutions at 10 mmol/L and a moderate rejection of Ca2+/Mg2+ ions ( 80%) for six out of eight selected pharmaceuticals (PhACs). The ATR-FTIR spectra and XPS analysis showed that BA could interfere the polymerization between PIP and TMC in forming the membrane active layer while the cross-linking degree between BA and TMC was relatively low. This implied that the proposed treatment target could also be achieved by using some other acidic diamines with similar functionalities of BA.

Haloacetaldehydes (HALs) are the third prevalent group of disinfection by-products (DBPs) by weight in drinking water, and their cytotoxicity and genotoxicity are higher than regulated DBPs. In order to understand their formation mechanism during chlorination and ozonation-chlorination, this study examined the reaction kinetics of chloral hydrate (CH), dichloroacetaldehyde (DCA), chloroacetaldehyde (CA) and acetaldehyde by chlorine at different pH values and chlorine doses. The results showed that the reaction rate constants increased with pH and chlorine dose, except that the degradation of CH would not be affected by the presence of free chlorine. At the same pH and chlorine dose, the half-lives of CH, DCA, CA and acetaldehyde were in the order of CH > acetaldehyde ≫ DCA > CA. A kinetic model used to predict the formation of HALs and chloroform during chlorination of acetaldehyde was developed, and the predicted data fitted well with the measured data. As pre-ozonation could oxidize natural organic matter to acetaldehydes, the concentration of acetaldehyde formed after pre-ozonation was used to calculate the HAL yields during ozonation-chlorination by the kinetic model, which fitted the experimental results well. The kinetic model elucidated that the formation mechanism of HALs was a stepwise substitution process on the α-hydrogen of acetaldehyde during chlorination.

Nanofiltration (NF) using loose membranes has a high application potential for advanced treatment of drinking water by selectively removing contaminants from the water, while membrane fouling remains one of the biggest problems of the process. This paper reported a seven-month pilot study of using a loose NF membrane to treat a sand filtration effluent which had a relatively high turbidity (∼0.4 NTU) and high concentrations of organic matter (up to 5 mg/L as TOC), hardness and sulfate. Results showed that the membrane demonstrated a high rejection of TOC (by

Ozone has been widely applied in drinking water and wastewater treatment plants, and it is essential to determine the ozone dosage and its ratio in ozone contact tank to increase the ozone absorption and utilization rates. Batch experiments were performed to determine the first-order reaction rate coefficient of ozone (k

Shale gas fracturing flowback water (SGFFW) contains a high concentration of colloids and organics which can cause severe water flux decline for membrane distillation (MD). It is desirable to identify the key foulants for MD fouling/wetting for real SGFFW treatment. In this study, coagulation and membrane filtrations with different molecular weight cut-off (MWCO) were applied to try to separate the different fractions of pollutants and evaluate their contributions to MD flux decline. The organics with a molecular weight of 20 kDa, which also belonged to humic acid-like components, protein-like components and fulvic acid-like components removed by coagulation could effectively mitigate MD fouling. However, the rest of the fractions of high molecular weight components of 20 kDa and low molecular weight components (i.e., 200 Da) removed by the UF membrane, had a less significant effect on the water flux of MD. Despite the further removal of small molecular weight compounds and Ca2+/Mg2+ by NF, negligible change for the water flux could be observed, indicating that the rest of the aromatic protein (21.2%) could still cause severe wetting for the MD membrane. In addition, SEM-EDS demonstrated that the combination of organic fouling and crystallization of Ca and Ba contributed to the fouling of the MD membrane. These studies demonstrated that the removal of high molecular weight organics by coagulation and removal of aromatic protein with the molecular weight of 200 Da might be vital for the alleviation of MD fouling or wetting.

Fluoroquinolones (FQs) are very ubiquitous in water environment in China. The commonly application of free available chlorine (FAC) during water treatment stimulated the focus on the transformation of FQs during chlorination. Among these FQs, norfloxacin (NOR) and ofloxacin (OFL) are the representatives of secondary amine FQs and tertiary amine FQs, respectively. To better understand the difference between secondary amine FQs and tertiary amine FQs during chlorination, reaction kinetics, products and mechanisms were determined. The maximum kapp of NOR were four orders of magnitude higher than that of OFL. Moreover, eleven products of NOR and twelve products of OFL were obtained by LC-MS/MS analysis. For the two FQs, the common reactive sites were three nitrogen atoms, benzene ring, carboxyl group and double bond by chlorination. For OFL, the ether ring was also active in aqueous system. The formation mechanisms of these products were presented in this study. The main reaction pathways were electrophilic addition to nitrogen, nucleophilic substitution to benzene ring, halodecarboxylation of carboxyl group and hydrolysis of ether ring. Na2S2O3 as a reducing agent had large effect on the chlorination of secondary amine FQ, but no effect on tertiary amine FQ. Be different to secondary amine FQ, the opening of quinolone ring happened in tertiary amine FQ after halodecarboxylation of carboxyl group.

The application of membrane technology to separate and extract target ions, such as lithium or chlorine, has recently seen considerable growth as a research topic, driven by the growing demand for energy and the environmentally friendly status of this technology. Based on the alternating current electric field layer-by-layer assembly technology, we report in this work target ionic control membrane surface multilayers with ion channels and ion exchange sites to control selective ion separation in electrodialysis. The reported surface multilayers utilize ion interactions between electric field force and charged groups and the mechanics of the target ion controlling the construction of ion exchange sites in an oppositely charged polymer layer and target ion channels in a like-charged monomer layer. The resulting membranes act as a strong barrier for multivalent ions, displaying a selective separation efficiency parameter equal to 99.99% for PO43−/Cl− and 99.99% for SO42−/Cl− in the resulting anion exchange membrane, and 83.70% for Mg2+/Li+ and 64.51% for Ca2+/Li+ in the resulting cation exchange membrane. Contrary to the initial selective separation efficiency between monovalent ions (−16.50% for Br−/Cl− and −40.00% for K+/Li+), the resulting membranes remarkably enhanced the transport of the target ions more easily than for other monovalent ions (0.76% for Br−/Cl− and −9.10% for K+/Li+). This work suggests promising new quantum mechanics of ion and electric field-based ionic control concepts to synthesize membranes with the ability to selectively separate a target ion.

Advances in treatment technologies of shale gas production wastewater are needed to minimize its toxic potency in polluted water sources. An aerated electrolysis (AE) process was employed for treat...

Size exclusion is the predominant mechanism of nanofiltration (NF) for the removal of organic pollutants in water. Saccharides and polyethylene glycols (PEGs) are most widely used as probe solutes for the determination of average pore radius and molecular weight cut-off (MWCO) of NF membranes, respectively. The rejection behaviors of saccharides and PEGs are however different due to the difference in molecular geometry, making the average pore size and MWCO be hardly interchangeable. This study was devoted to associate the rejection of PEGs with that of saccharides by introducing the concept of effective solute radius which is different from the Stokes radius primarily in the aspect of preferential orientation. The rejection data of three saccharides and three PEGs by four commercial NF membranes were utilized. The lower rejection of PEGs than saccharides was more apparent for the tight membranes than for the loose membranes. The effective radii of a same PEG were different for the four membranes. An explicit equation was successfully established based on a geometric model which relates the effective radius of a solute with its width, length to width ratio and the effective orientation angle through a membrane. The PEGs always took a more horizontal orientation relative to the membrane pores during permeation. A smaller pore size and a longer molecule chain resulted in a higher orientation angle. The solute effective orientation was further related to the ratio of solute Stokes radius to membrane pore radius by an empirical formula with a same fitting coefficient for the three PEGs. This study provides valuable implications on the interpretation and prediction of the rejection of linear solutes by NF membranes.

Adsorption of trace organic compounds (TrOCs) onto the membrane materials has a great impact on their rejection by nanofiltration (NF) and reverse osmosis (RO) membranes. This study aimed to investigate the difference in adsorption of various pharmaceuticals (PhACs) onto different NF/RO membranes and to demonstrate the necessity of isolating the polyamide (PA) active layer from the polysulfone (PS) support layer for adsorption characterization and quantification. Both the isolated PA layers and the PA+PS layers of NF90 and ESPA1 membranes were used to conduct static adsorption tests. Results showed that apparent differences existed between the PA layer and the PA+PS layer in the adsorption capacity of PhACs as well as the time necessary to reach the adsorption equilibrium. PhACs with different physicochemical properties could be adsorbed to different extents by the isolated PA layer, which was mainly attributed to electrostatic attraction/repulsion and hydrophobic interactions. The PA layer of ESPA1 exhibited apparently higher adsorption capacities for the positively charged PhACs and similar adsorption capacities for the neutral PhACs although it had significantly less total interfacial area (per unit membrane surface area) for adsorption compared to the PA layer of NF90. The higher affinity of the PA layer of ESPA1 for the PhACs could be due to its higher capacity of forming hydrogen bonds with PhACs resulted from the modified chemistry with more –OH groups. This study provides a novel approach to determining the TrOC adsorption onto the active layer of membranes for the ease of investigating adsorption mechanisms.

Shale gas fracturing flowback water (SGFFW) generated during shale gas extraction is of great concern due to its high salinity and complicated components. In this study, the feasibility of nanofiltration (NF) and reverse osmosis (RO) for SGFFW desalination in assisting SGFFW reuse and discharge were systematically evaluated after the pretreatment of coagulation-ultrafiltration (UF) process. Under the same initial water flux of 1.27 × 10 −6 m/s, the water flux decreased tremendously within 800–1000 min for both NF(NF90) and low pressure RO(ESPA1) membranes. The stable water flux was only 38.2% and 15.8% of the initial water flux for NF90 and ESPA1 membrane, respectively. The removal efficiency of the Na + was 81.2% for NF90 membrane and 88.1% for ESPA1 membrane, while the rejection ratios of Cl − were 83.3% and 87.3% for NF90 and ESPA1 membrane, respectively. The rejection ratios for multivalent ions (i.e., Fe 3+ , Ca 2+ and Ba 2+ ) were typically very high (>90%). According to fluorescence regional integration (FRI) under the Excitation—Emission—Matrix Spectra (EEM) within each region volume, the dissolved organics removed by NF in different region decreased in the order of VI (86.0%), I (47.2%), III (31.8%), II (20.8%), V (6.2%), IV(0.2%), while the overall rejection ratio of RO decreased in the order of VI (100.0%), I (88.3%), II (70.7%), III (66.8%), V (58.9%), IV(0.3%). The difference in molecular weight(MW) distribution between the feed and permeate of NF/RO samples showed that the organics with MW of 20 kDa were greatly removed, indicating the NF/RO mainly intercepted this portion of organics such as guar gum, polyacrylamide and various surfactants. However, the effluent of the NF/RO still contained a large portion of biopolymers, which was plausible that small portion of polyacrylamide passed through the membrane. The elemental analysis by scanning electron microscope (SEM)-energy dispersive spectrometer (EDS) demonstrated the fouling layer was mainly composed of organics (i.e., polyacrylamide and aromatic protein). It seemed that developing new-type anti-fouling membrane was a feasible approach to decelerate the membrane fouling.

The solute-membrane interactions between trace organic compounds (TrOCs) and nanofiltration (NF) or reverse osmosis (RO) membranes result in the adsorption of TrOCs onto membranes and in turn affect the rejection of TrOCs. This study investigated the adsorption and rejection of four positively charged, two neutral and one negatively charged pharmaceuticals (PhACs) by four commercial NF/RO membranes to correlate the adsorbed amount and the steady-state rejection, and to quantitatively evaluate the role of various solute-membrane interactions in adsorption and rejection. The adsorbed amounts of PhACs were determined in static adsorption tests using the isolated polyamide (PA) layers when the RO and tight NF membranes were used, and were calculated from the decline of rejection during filtration when the two loose NF membranes were used. The impacts of electrostatic and non-electrostatic interactions (including hydrophobic interaction and hydrogen bonding) were quantified for positively charged PhACs by comparing the respective adsorption and rejection at neutral pH with that at the isoelectric point (IEP) of each membrane. Results showed that at neutral pH, the adverse effect of adsorption on the steady-state rejection was 65%). Electrostatic attraction was also found to cause the rejection of the tight membranes for the positively charged PhACs to decrease by 0.8–4.3%, that of the loose membranes to decrease by 13.4–28.3%, while the impact of non-electrostatic interactions on the rejection was 1.1–2.3% for the tight membranes and 4.0–9.8% for the loose membranes.

The electro-peroxone (E-peroxone) process is an emerging ozone-based electrochemical advanced oxidation process that combines conventional ozonation with in-situ cathodic hydrogen peroxide (H2O2) production for oxidative water treatment. In this study, the effects of the E-peroxone pretreatment on disinfection by-product (DBP) formation from chlorination of a synthetic surface water were investigated and compared to conventional ozonation. Results show that due to the enhanced transformation of ozone (O3) to hydroxyl radicals ( OH) by electro-generated H2O2, the E-peroxone process considerably enhanced dissolved organic carbon (DOC) abatement and significantly reduced bromate (BrO3−) formation compared to conventional ozonation. However, natural organic matter (NOM) with high UV254 absorbance, which is the major precursors of chlorination DBPs, was less efficiently abated during the E-peroxone process than conventional ozonation. Consequently, while both conventional ozonation and the E-peroxone process substantially reduced the formation of DBPs (trihalomethanes and haloacetic acids) during post-chlorination, higher DBP concentrations were generally observed during chlorination of the E-peroxone pretreated waters than conventional ozonation treated. In addition, because of conventional ozonation or the E-peroxone treatment, DBPs formed during post-chlorination shifted to more brominated species. The overall yields of brominated DBPs exhibited strong correlations with the bromide concentrations in water. Therefore, while the E-peroxone process can effectively suppress bromide transformation to bromate, it may lead to higher formation of brominated DBPs during post-chlorination compared to conventional ozonation. These results suggest that the E-peroxone process can lead to different DBP formation and speciation during water treatment trains compared to conventional ozonation.

This study was conducted in order to obtain a better understanding of the combined fouling by biopolymers coexisting with inorganic particles from the aspects of fouling index, fouling layer structure and biopolymer−particle interactions. Calcium alginate was used as the model biopolymer and Fe 2 O 3 , Al 2 O 3 , kaolin, and SiO 2 were used as model inorganic particles. Results showed that the combined fouling differed greatly among the four types of inorganic particles. The differences were attributed particularly to the different adsorption capacities for calcium alginate by the particles with this capacity decreasing in the order of Fe 2 O 3 , Al 2 O 3 , kaolin and SiO 2 . Particle size measurement and electron microscopic observation indicated the formation of agglomerates between calcium alginate and those inorganic particles exhibiting strong adsorption capacity. A structure was proposed for the combined fouling layer comprised of a backbone cake layer of alginate−inorganic particle agglomerates with the pores partially filled with discontinuous calcium alginate gels. The filterability of the fouling layer was primarily determined by the abundance of the gels. The strength of physical interaction between calcium alginate and each type of inorganic particle was calculated from the respective surface energies and zeta potentials. Calculation results showed that the extent of physical interaction increased in the order of Al 2 O 3 , Fe 2 O 3 , kaolin and SiO 2 , with this order differing from that of adsorption capacity. Chemical interactions may also play an important role in the adsorption of alginate and the consequent combined fouling. High-resolution XPS scans revealed a slight shift of electron binding energies when alginate was adsorbed.

Reusing treated wastewater can effectively alleviate water shortages and water contamination problems but depends on ensuring the safety of the reclaimed water that is produced. The operating and management conditions for water reclamation plants in China have been changed since the outbreak of the COVID-19 epidemic in China at the end of 2019 to prevent emerging viruses being spread through wastewater treatment processes and the reclaimed water that is produced. Removal of pathogens and trace organic compounds (e.g., pharmaceuticals and personal care products and endocrine disrupting chemicals) in a real water reclamation plant after the start of COVID-19 epidemic was studied. Disinfection byproduct formation caused by chlorine being added to meet disinfection requirements was also assessed. The pathogenic microorganism concentrations in effluent were 80% when advanced treatments were performed using ozone, ultraviolet light, and chlorine doses of 2 mg/L, 20.5 mJ/cm2, and 2-3 mg/L, respectively. The main disinfection byproduct produced at a chlorine dose of 2 mg/L and a residence time of 1 h was chloroform (at concentrations

Interactions of trace organic compounds (TOrCs) with polymeric nanofiltration (NF) membrane can affect their rejection. It is desirable to investigate whether solubility which depends on the free energy of interaction between these solutes and water correlates with rejection/adsorption and the potential to be incorporated in the partitioning terms of current NF model. A total of ten neutral disinfection by-products (DBPs) were selected as the model compounds for TOrCs to comprehensively investigate the role of solubility on rejection and adsorption. Pearson correlation analysis indicated that the correlation between MW and rejection ratio was highly significant (r = 0.778, p = 0.008) and that between solubility and rejection ratio was moderately significant (r = -0.636, p = 0.48) in a cross-flow system. By fitting Freundlich equation from adsorption isotherm experiment, the adsorption affinity (K f) of DBPs was roughly correlated with their solubility with regard to the comparison of n value with 1. α was then introduced as a parameter of solute-membrane interaction from the perspective of partitioning term in the hydrodynamic model. Exponential relationship can be observed between the solubility and α, demonstrating the possibility of incorporating solubility into the partitioning terms in NF model to accurately predict the rejection of DBPs.

The chlorination of azo compounds can produce halonitromethanes (HNMs), which have attracted increasing concern due to their high genotoxicity. By impacting the speciation of chlorine and azo compounds, pH impacts apparent second-order rate constants of Methyl Orange (MO, 27.5-1.4 × 103 M-1 s-1), Acid Orange II (AO, 16.7-99.3 M-1 s-1), and Acid Red 1 (AR 1, 3.7-72.5 M-1 s-1) (pH range 6.3-9.0). The two-compartment first-order model successfully described the chloropicrin (TCNM) formation kinetics, suggesting that both fast- and slow-reacting precursors of TCNM are generated from the chlorination of azo compounds. The ratios between fast and slow formation rate constants for MO and AO were 15.6-5.4 × 102, while that of AR 1 was 9.8-19.4 (pH range 6.5-9.0). The fraction of the fast-reacting TCNM precursors decreased with increasing pH for MO and AO; while that for AR 1 decreased when pH increased from 6.5 to 8.0, and then increased when pH increased from 8.0 to 9.0. The impact of pH on TCNM formation was also precursor-specific. The highest molar yields of TCNM predicted from the model in this study were 2.4%, 2.5%, and 1.5% for MO, AO, and AR 1, respectively. The study demonstrates that azo compounds are important HNM precursors, and pose a potential threat to drinking water safety.

Shale gas fracturing flowback water (SGFFW) generated during shale gas extraction is of great concern and recycling for another fracking is the common disposal way. In this study, the feasibility of coagulation–UF hybrid process in assisting SGFFW reuse was systematically evaluated. Organics in SGFFW of Fuling were comparable with that reported in Marcellus. Poly aluminium chloride (PAC) dosage of 1500 mg/L may be preferred due to relatively low TOC (16.02 mg/L) and turbidity (3.03 NTU) in permeate and similar water flux (4.0×10−4 m/s) with that under the dosage of 2000 mg/L. With increase dosage of PAC, fouling mechanism changed from complete blocking to intermediate-blocking or cake standard. SEM-EDS indicated foulant was rich in carbon and oxygen with iron oxide and sulfate precipitates. According to volumetric integration method, overall rejection ratio for organics in different region in hybrid process decreased in the order of V (89.0%), IV 86.2%, III (80.3%), II (77.7%), I (55.2%) and VI (49.3%). LC-OCD illustrated coagulation mainly removed the organics with molecular weight of 20 kDa, while UF could remove a fraction of low molecular weight components (i.e., 200 Da). Fouling was reversible by backwashing and thus hybrid process without sedimentation can be potentially used for SGFFW treatment.

In this study, we proposed to apply an integrated process which is comprised of in situ ozonation, ceramic membrane filtration (CMF) and biologically active carbon (BAC) filtration to wastewater reclamation for indirect potable reuse purpose. A pilot-scale (20 m3/d) experiment had been run for ten months to validate the prospect of the process in terms of treatment performance and operational stability. Results showed that the in situ O3 + CMF + BAC process performed well in pollutant removal, with chemical oxygen demand, ammonia, nitrate nitrogen, total phosphorus and turbidity levels in the treated water being 5.1 ± 0.9, 0.05 ± 0.01, 10.5 ± 0.8, 96%. This study demonstrated that synergistic effects existed in the in situ O3 + CMF + BAC process. Compared to pre-ozonation, in situ ozonation in the membrane tank was more effective in controlling membrane fouling (maintaining operational stability) and in degrading organic pollutants, which could be attributed to the higher residual ozone concentration in the tank. Because of the removal of particulate matter by CMF, water head loss of the BAC filter increased slowly and prolonged the backwashing interval to 30 days. BAC filtration was also effective in removing ammonia and N-nitrosodimethylamine from the ozonated water.

Metal-organic frameworks (MOFs), a class of hybrid organic-inorganic materials, have recently attracted tremendous interests in the fabrication of thin-film nanocomposite (TFN) membranes with exceptional permselectivity. However, the structure-performance relationship of such membranes, which is a function of both MOF type and membrane fabrication procedure, has not been elucidated in the literature. In this study, three types of hydro-stable MOFs, namely, MIL-53(Al), NH2-UiO-66, and ZIF-8, were used to fabricate TFN nanofiltration membranes via both blending (BL) and preloading interfacial polymerization methods. Results show that the incorporation of MOFs could enhance water permeability of TFN membranes to 7.2 L/(m2·h·bar) at most ( TFNNH2-UiO-66-BL-0.10%), about 1.3 times of the corresponding thin-film composite membranes, without sacrificing their selectivity to reject NaCl (>40%) and xylose (>65%). Membrane characterization revealed that MOFs decreased the cross-linking degree while increasing the membrane thickness, surface negative charge, and roughness of the polyamide active layer. MIL-53(Al) were found to bind with polyamide via reacting with piperazine, whereas weaker polyamide-MOF interactions were observed for NH2-UiO-66 and ZIF-8. This difference, along with the hydrophilicity of MOF particles, explained the varied permselectivity of different TFN membranes. Compared to pristine polyamide membranes, the TFN membranes demonstrated higher or comparable efficiencies in removing a set of six pharmaceuticals (PhACs), which were determined by the molecular properties of PhACs and membrane structure. The findings of this study deepen our understanding of the roles that MOFs play in regulating membrane performance, promoting molecular design of MOF-incorporated TFN membranes via precise control of MOF-polymer interactions.

Formation of brominated disinfection by-products (DBPs) from bromide and natural organic matter upon chlorination imposes health risks to drinking water users. In this study, capacitive deionization (CDI) was evaluated as a potential process for DBP precursor removal. Synthetic humic acid and bromide containing saline water was used as model water prior to CDI treatment. Batch experiments were conducted at cell voltages of 0.6-, 0.9-, and 1.2 V to study the influence of CDI on the ratio of bromide and dissolved organic carbon, bromine substitution factor, and DBP formation potential (FP). Results showed beneficial aspects of CDI on reducing the levels of these parameters. A maximum DBPFP removal from 1510 to 1160 μg/L was observed at the cell voltage of 0.6 V. For the removed DBPFP, electro-adsorption played a greater role than physical adsorption. However, it is also noted that there could be electrochemical oxidations that led to reduction of humic content and formation of new dichloroacetic acid precursors at high cell voltages. Because of the potential of CDI on reducing health risks from the formation of less brominated DBPs upon subsequent chlorination, it can be considered as a potential technology for DBP control in drinking water treatment.

Haloacetaldehydes (HAs) are the third prevalent group of disinfection by-products (DBPs) of great health concern. In this study, their formation and speciation during chlorination were investigated for raw and process waters collected at three O3-biological activated carbon (BAC) advanced drinking water treatment plants. The results showed that all HA formation potentials (HAFPs) were highly enhanced whenever ozone was applied before or after conventional treatment. Sand filtration and BAC filtration could substantially reduce HAFPs. Trihalomethanes (THMs) were also measured to better understand the role of HAs in DBPs. Very different from HAFPs, THMFPs kept decreasing with the progress of treatment steps, which was mainly attributed to the different precursors for HAs and THMs. Brominated HAs were detected in bromide-containing waters. Chloral hydrate (CH) contributed from 25% to 48% to the total HAs formed in waters containing 100-150 μg L(-1) bromide, indicating the wide existence of other HAs after chlorination besides CH production. In addition, bromide incorporation factor (BIF) in HAs and THMs increased with the progress of treatment steps and the BIF values of THMs were generally higher than those of HAs. The BAC filtration following ozonation could significantly reduce HA precursors produced from ozonation but without complete removal. The brominated HAFPs in the outflow of BAC were still higher than their levels in the raw water. As a result, O3-BAC combined treatment was effective at controlling the total HAs, whereas it should be cautious for waters with high bromide levels.

Disinfectant-enhanced backwash is frequently required to control the over-growth of biomass in biologically active carbon (BAC) filters for drinking water treatment. This study was conducted to investigate the impact of different backwashing strategies on the biodegradation and adsorption performance of BAC filters and attached biomass concentration in the filters. The biodegradation performance was evaluated using the three chloroacetic acids (CAAs) as indicator chemicals. Results showed that both free chlorine- and chloramines-enhanced backwashes could significantly increase the removal efficiency of attached biomass, but they also impaired the CAA degradation in BAC filters. The deterioration of CAA degradation could not be correlated with the removed attached biomass. Use of CAAs was a feasible approach to evaluate the biodegradation performance of BAC filters either during operation or after backwash. Chloramines-enhanced backwash is suggested to be employed to sustain the operation of BAC filters when excessive biomass growth takes place, due to its higher efficiency in removing attached biomass and lower adverse impact on BAC adsorption properties compared with free chlorine-enhanced backwash. However, the more pronounced adverse impact on organic matter degradation and the inconvenience of using chloraminated water must be considered.

Nitro-based compounds are the direct precursors of trichloronitromethane during chlorination disinfection. Two nitro-based pharmaceuticals ranitidine and nizatidine were selected as model compounds to assess the effect of oxidation on the removal of nitro-based pharmaceuticals, as well as the reduction of their trichloronitromethane formation potentials (TCNMFPs). The four oxidants were ozone (O3), chlorine (Cl2), chlorine dioxide (ClO2) and potassium permanganate (KMnO4). The changes in pharmaceuticals and their TCNMFPs during oxidation using various oxidants and dosages were quantified. The relationships between oxidation product structures and TCNMFP changes were also analyzed. The results showed that oxidation with Cl2 and KMnO4 were more effective than ClO2 and O3 in removing the nitro-based pharmaceuticals. Meanwhile, decreased TCNMFPs by KMnO4 oxidation but increased TCNMFPs by Cl2, ClO2 and O3 oxidation were observed. The results of product analysis indicated that chlorine transfer products had higher TCNMFPs, while oxygen transfer products made little contribution to TCNMFPs after oxidation. In addition, one possible reaction pathway leading TCNMFP increase was that chloro-nitromethane or nitromethane, which was a better TCNM precursor, formed when double bond was attacked by oxidants.

This study evaluated the feasibility of forward osmosis (FO) in diluting and reusing the concentrate produced in a reverse osmosis (RO) plant in James City County, VA. Secondary treated wastewater (STW) was used as the feed solution. Findings indicated that pH had slight effects on the water flux of the FO membrane. As the concentration of total dissolved solids (TDS) in the concentrate was diluted from 12.5 to 1.0 g/L or the temperature in the STW decreased from 23 to 10 °C, the membrane flux decreased from 2.2 to 0.59 and 0.81 L/(m2 h), respectively. The FO membrane showed a good performance in the rejection of organic pollutants, with only a small part of the protein-like substances and disinfection byproducts permeating to the diluted concentrate. During an 89-hour continuous operation, water flux decline due to membrane fouling was not observed. Controlling the TDS in the second-stage FO effluent at 1.5 g/L, approximately 8.3% of the pump energy input could be saved. The consumption of groundwater was reduced from 22.7 × 103 to 10.6 × 103 m3/d. FO was proved to be an effective method in both diluting the discharged concentrate and reducing the energy consumption of RO.

The effects of calcium, cupric, ferrous and ferric ions on the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) were investigated using natural organic matter (NOM), small molecular weight NOM surrogates and natural water samples. The results showed that the effects were greatly dependent on the disinfection byproduct (DBP) precursor structure and molecular weight, and metal ions species. While using NOM as precursors, addition of 4.00 mM calcium ions increased the formation of THMs, dihaloacetic acids (DHAAs) and trihaloacetic acids (THAAs) by 24-47%, 51-61% and 15-25%, respectively. Addition of cupric ions at 0.02 mM increased the formation of THMs and DHAAs by 74-83% and 90-100%, respectively, but decreased the formation of THAAs by 26-27%. Similar effect was not observed when 0.04 mM ferrous or ferric ions were added. The effects of calcium and cupric ions on DBP formation were generally more evident for the NOM surrogates than that for NOM. The primary catalytic effect of calcium ions was due to complexation and less sensitive to molecular structure or weight, while that of cupric ions was attributed to redox reactions and greatly dependent on molecular structure. Both ferric and ferrous iron had substantial effects on the DBP formation of surrogates (citric acid and catechol in particular), which implied that the catalytic effects of ferric and ferrous iron mainly depended on molecular weight. The catalytic effect of cupric ions was also observed on natural water samples, while the effects of calcium, ferrous and ferric ions on natural water samples were not evident.

Ozone process has been widely used for drinking water treatment recently. In the oxidation process, bromate is formed by three pathways, i.e., the direct pathway, the direct-indirect pathway and the indirect-direct pathway. This study developed a method to calculate the percentage of these three pathways for bromate formation during O 3 process and O 3 /H 2 O 2 process. Two kinds of water, distilled water containing bromide (DW) and surface water from the Yellow River (SW) were selected as raw rater. The result showed that in natural water systems, the direct-indirect pathway was dominant for bromate formation during the oxidation process. When 3 mg L −1 O 3 was used as the only oxidant, nearly 26% of bromide ion was transferred into bromate in two kinds of water after 80 min. The dominant pathway in DW was the direct pathway (48.5%) and the direct-indirect pathway (46.5%), while that was the direct-indirect pathway (68.9%) in SW. When O 3 /H 2 O 2 were used as oxidants, as the H 2 O 2 dosage increased, the fractions of bromate formation by direct pathway and direct-indirect pathway decreased, while that by indirect-direct pathway increased. The conversion ratio from bromide to bromate first kept stable or increased, then decreased and reached its minimum when [H 2 O 2 ]/[O 3 ] ratio was 1.0 in DW and 1.5 in SW. Under this condition the indirect-direct pathway took the largest fraction of 70.7% in DW and 64.0% in SW, respectively.

Membrane fouling especially organic fouling of nanofiltration (NF) membranes is notorious but yet remains not fully understood. This study was conducted to identify the key organic substances responsible for organic fouling and quantify the individual and interactive effects of these key foulants on organic fouling, primarily by using statistical methods. A total of ten different water, covering lake water and water collected from water and wastewater treatment plants, were filtered to obtain the fouling potential and determined for organic and inorganic components. Pearson correlation showed that fouling potential could correlate with TOC with a moderate significance. Partial correlation revealed that, in addition to polysaccharides and protein-like substances, fulvic acid-like substances could act as key foulants to organic fouling of NF membranes, though protein-like and fulvic-like substances were mutually highly correlated. Generally, most polysaccharides were macromolecules (>10 kDa) while protein-like and fulvic acid-like substances were more of low molecular weight. A regression equation was established between fouling potential and the three types of key foulants; the calculated value by this equation matched well with the experimental result especially when the fouling potential was relatively high. Variance partitioning analysis showed that individual contributions to organic fouling by polysaccharides, protein-like and fulvic acid-like substances were all lower than 30%, while the interactive effect among these three components was as high as 66% ± 7%. This suggested that organic fouling was a complex process with the three key types of foulants involved simultaneously. Spearman correlation showed that higher contents of polysaccharides and protein-like substances in feed water generally led to a faster accumulation of these two types of foulants (determined from FTIR results) onto membrane, respectively, but not necessarily resulted in a heavier organic fouling.

Aesthetics and water quality are primary issues of concern for sustainable water reuse since aesthetically unpleasant color and odor are likely to induce public misgiving. This study utilizes aesthetic indicators and other bulk water quality parameters for evaluation. It is found that ozonation during advanced treatment processes in a full-scale water reclamation plant (WRP) could achieve satisfactory performance in decolorization and oxidation of aromatic and humic contents. As limited efficacy on odor removal was detected in the WRP, this study further researched the removal of the main odorant substances 2-methylisokanol (2-MIB) and geosmin (GSM) with different ozone dosage using solid-phase extraction (SPE) and gas phase mass spectrometry (GC–MS) techniques. According to the first-order reaction kinetics, it is inferred that competitive reactions during ozonation by organic matters and restricted CT values are major factors affecting the odor removal. As such, additional treatment approaches such as nanofiltration (NF) are suggested to be consider for aesthetic control towards sustainable and long-term reclaimed water use.

Porous organic polymers have been considered promising for the design of high performing membranes, mainly because of their superior surface area, intrinsic mesoporous structure and good polymer affinity. In this study, hierarchical o-hydroxyazo porous organic polymers (o-POPs) and piperazine (PIP) monomers were incorporated into the casting solution, followed by phase inversion to prepare PIP-containing polymeric substrates. The o-POPs modified thin film nanocomposite (TFN) membranes were fabricated by interfacial polymerization (IP) with trimesoyl chloride (TMC). The incorporated o-POPs could locally enrich PIP in substrates and impede its diffusion towards the organic interface during IP reaction through hydrogen bonding and physical obstruction, leading to the formation of a crumpled membrane surface. The enhancement of surface roughness and hydrophilicity endowed the TFN membranes with a signally elevated water permeance while maintaining a comparable solute rejection. The optimal TFN membrane with the o-POP content of 0.3 wt% displayed a remarkable water permeance of 29.6 L m−2 h−1 bar−1, a high Na2SO4 rejection of 94.9%, and an efficient removal of reactive dyes (e.g., reactive black 5 and reactive orange 16, >98.2%), which makes o-POP functionalized TFN membranes competitive for NF applications in water treatment.

Water utilities must disinfect their water despite the formation of carcinogenic disinfection byproducts (DBPs) such as haloacetic acids (HAAs) upon chlorination. Although employment of a biologically active carbon (BAC) filtration process is able to reduce the HAA level preventively by removing the HAA precursors and correctively by removing the already-formed HAAs, this research reported an HAA leap in a bench-scale BAC filter effluent upon a disinfectant switch from chlorine to chloramine, posing a pressure of meeting the stringent HAA regulations. The HAA6 (sum of six HAAs) tripled from a 5 μg/L base level to a maximum of 17 μg/L during progressive switches with 3 chloramine doses at 5, 25, and 50 mg/L. Dichloroacetic acid (DCAA) accounted for the majority of the leap, which also influenced the bromine substitution factor during the HAA formation. Filtration of distilled water using heat-deactivated media evidenced slight HAA desorption and suggested potential roles of soluble microbial products from biofilms as new HAA precursors for a real BAC filter experiencing a disinfectant switch.

The incorporation of nanomaterials into a polyamide (PA) matrix has been demonstrated to be effective in the design of advanced thin film nanocomposite (TFN) membranes. In this study, a novel TFN membrane was developed by simultaneous introduction of two nanofillers with different dimensions. Graphitic carbon nitride (g-C3N4) and halloysite nanotubes (HNTs) were co-deposited onto a substrate surface with piperazine (PIP) monomers via vacuum filtration, followed by interfacial polymerization (IP) with trimesoyl chloride (TMC). A series of characterizations showed that the pre-loaded g-C3N4 was present as nanoaggregates wrapped by the formed PA film, while one-dimensional HNTs inclined to be horizontally aligned as a hydrophilic interlayer. This unique architecture led to a crumpled membrane surface with convex and ridged structures, and provided additional water transport channels. The surface roughness and hydrophilicity of the TFN membranes were also enhanced with the addition of nanomaterials. Although g-C3N4 and HNTs were able to elevate the water permeance, a superior separation performance could only be achieved by simultaneously incorporating these two nanofillers. The best performing TFN membrane containing 16.4 μg cm−2 g-C3N4 and 19.7 μg cm−2 HNTs exhibited a water permeance of 20.5 L m−2 h−1 bar−1, nearly twice as high as that of the thin film composite (TFC) membrane, while maintaining a comparably high Na2SO4 rejection of 94.5%. This demonstrated the effectiveness of g-C3N4 and HNTs in developing high-performance TFN membranes, which were ascribed to their respective advantages as well as the combined effect in the regulation of the PA layer microstructure.

The direct photo-transformation of widely used antibiotics, including Tetracycline (TTC), chlortetracycline (CTC), sulfamethoxazole (SMX) and sulfamethazine (SMZ) were quantified for surface water by using artificial UV irradiation. The photolysis rate is directly proportional to the overlap between the absorption spectrum of the solution and the spectrum of the terrestrial sunlight. Increasing overlap fraction of Tetracycline (TC) group than Sulfanomide (Sulfa) group, the transformation of TC group is certified much faster than the sulfa group. The speciation of TC and Sulfa group antibiotics are pH-dependent and consequently influence its light adsorption spectrum. And the toxicity of the four target antibiotics along the photo-transformation was assessed. In field aquatic environment, a temporal- and spatial half-life model described the behavior of the antibiotics in water column of victoria harbour could be validated by using experimentally obtained quantum yield with the target field meteorological data. The modeling results indicated the photolysis rate of different kind of antibiotics varied differently along season, daily time and water depth. Summer, midday and surface layer of water body would be the time- and space-highlight spot in which the phototransformation are the dominant process for antibiotics concentration depletion. Seasonal variety would be enhanced for sulfa-group kind antibiotics, which having only tail overlapped with irradiation spectrum. Daily averaged half-lives of TC group were relatively stable, while the sulfa group antibiotics were found to vary from about 300 to 750 h, dependent on the seasonal change.

Accidental spills and surface discharges of shale gas produced water could contaminate water resources and generate health concerns. The study explored the formation and speciation of disinfection by-products (DBPs) during chlorination of natural waters under the influence of shale gas produced water. Results showed the presence of produced water as low as 0.005% changed the DBP profile measurably. A shift to a more bromine substitution direction for the formation of trihalomethanes, dihaloacetic acids, trihaloacetic acids, and dihaloacetonitriles was illustrated by exploring the individual DBP species levels, bromine substitution factors, and DBP species fractions, and the effect was attributable to the introduction of bromide from produced water. The ratio of dichloroacetic and trichloroacetic acids also increased, which was likely affected by different bromination degrees at elevated bromide concentrations. Increasing blend ratios of produced water enhanced the formation of DBPs, especially the brominated species, while such negative effects could be alleviated by pre-treating the produced water with ozone/air stripping to remove bromide. The study advances understandings about the impacts of produced water spills or surface discharges regarding potential violation of Stage 2 DBP rules at drinking water treatment facilities.

The rapid rise of shale gas development has triggered environmental and human health concerns due to its impacts on water resources, especially on disinfection byproduct (DBP) formation upon chlorination. Despite the recently reported results on bromide, the effects of non-bromide ions in production wastewater at extremely high levels are vaguely defined. In this study, we investigated the effects of production wastewater, with bromide and non-bromide species, on the formation of DBPs when production wastewater was spiked into surface waters at various percentages. Results showed that the introduction of debrominated production wastewater led to increased formation of some chlorinated DBP species in selected surface water and wastewater. As the spiking percentage of debrominated production wastewater increased, the chlorinated DBP species increased. The contributions of individual cations to DBP formation followed a sequence of magnesium > calcium > barium at 0.10% spiking percentage due to the different catalytic effects of their chelates with organic precursors. The study of anions suggested that the discharge of treated production wastewater containing elevated sulfate may further enhance DBP formation. The significance of this study lies in the fact that in addition to bromide concerns from production wastewater, non-bromide species also contributed to DBP formation. The gas production wastewater management decision should consider the negative impacts from both bromide and non-bromide species to better protect the receiving water resources.

Nano scale zero-valent iron (nZVI), a promising engineering technology for in situ remediation, has been greatly limited by quick self-corrosion and low mobility in porous media. Highly reactive nZVI particles produced from the borohydride reduction method were enclosed in a releasable Ca(OH)2 layer by the chemical deposition method. The amount of Ca(OH)2 coated on nZVI surface were well controlled by the precursor dosage. At moderate Ca(OH)2 dosage (RCa/TFe = 0.25) condition, the increment of Fe0 content for the obtained nZVI/Ca-0.25 sample was observed. The interfacial reactions between the iron oxide shell and the Ca(OH)2 saturated environment were delicately elucidated by the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectrum. And the coverage of Ca(OH)2 shell on spherical nZVI surface was found more complete and uniform for the nZVI/Ca sample obtained from the moderate precursor dosage condition (RCa/TFe = 0.25). The Ca(OH)2 shell before dissolution was demonstrated owning the anti-corrosion capability to slow down the oxidation of Fe0 core in air, during ethanol storage and in aqueous environment. The mechanism of anti-corrosion capability for nZVI/Ca-0.25 particle was interestingly found to be attributed to the Ca(OH)2 shell isolation and also be potentially due to the iron oxide shell phase transformation mediated by the outer Ca(OH)2 shell. An improved trichloroethylene reduction performance was observed for nZVI/Ca-0.25 than bare nZVI. The mobility of nZVI/Ca particles in water-saturated porous media was moderately improved before shell dissolution.

The DSPM&DE (Donnan steric pore model and dielectric exclusion) model was employed to predict the rejection of six haloacetic acids (HAAs) and six pharmaceuticals (PhACs), selected to have different molecular weight, hydrophobicity and charge, by two commercial nanofiltration (NF) membranes (HL and NF270). Increasing filtration pressures were applied to vary the rejection ratios. Glucose and NaCl were used as the probe solutes for the determination of the three adjustable parameters involved in the model. Results showed that the model could accurately predict the rejection of the HAAs by both NF membranes with general deviations less than 5%, but it generally over-predicted the rejection of the PhACs. According to the DSPM&DE model, diffusion was the predominant mass transport mechanism in the membrane for both the HAAs and the probe solutes. Experimental determination by conducting diffusion cell test however showed that diffusion only played a minor role in the overall mass transport normally with a contribution less than 10%. The disagreement of model calculation from experimental determination might be due to the improper quantification of the coefficients for solute partitioning between the water phase and the solid (membrane) phase and the hindrance factors for convection and diffusion by the DSPM&DE model. The high accuracy of the model in predicting the rejection of HAAs was owing to the high similarity in physicochemical properties of HAAs with the used probe solutes. If nizatidine were used as the probe solute, the rejection of ciprofloxacin and chloramphenicol by both HL and NF270 would be well predicted.

A biologically activate carbon (BAC) filter was continuously operated on site for the treatment of haloacetic acids (HAAs) in an outdoor swimming pool at an average empty bed contact time (EBCT) of 5.8 min. Results showed that BAC filtration was a viable technology for direct removal of HAAs from the pool water with a nominal efficiency of 57.7% by the filter while the chlorine residuals were 1.71 ± 0.90 mg/L during the study. THMs and TOC were not removed and thus were not considered as indicators of the effectiveness of BAC filtration. Increased EBCT in the range of 4.5 and 6.4 min led to improved HAA removal performance, which could be best fit by a logarithmic regression model. BAC filtration also affected the HAA speciation by removing more dichloroacetic acid (DCAA) than trichloroacetic acid (TCAA), resulting in a lower ratio of DCAA/TCAA in the filtered effluent. However, the observation of an overall constant ratio could be attributable to a complex formation and degradation mechanism occurring in swimming pools.

The filterability and the associated structure of fouling layers formed from calcium alginate coexisting with ferric iron were investigated in this study. Filterability was assessed by using both specific resistance and material properties. The change of ferric iron from more “fresh” to more “aged” forms was considered. The ferric iron molar content was varied from 0% to 100% of calcium ions which were just sufficient for gel layer formation (2.53 mmol per gram alginate). Results showed that ferric content higher than ~30% could substantially increase the fouling layer filterability, although the influence by fresh ferric was much more significant than the aged due to the coagulating effect exerted by the former. The aged ferric iron was relatively inert and believed to have less interactions with the calcium alginate gel layer. When the ferric iron content was sufficiently low (i.e. no more than 15% of the calcium content), little influence on the fouling layer filterability was observed. The aging of ferric iron in the alginate dispersion had significant impact on fouling layer filterability in a time scale of days. The difference in filterability of various fouling layers was mostly attributed to the difference in physical structure. SEM observation of the freeze-dried specimen showed that the gel layer had a very porous structure with isolated cavities by thin films that may effectively obstruct water passage. In comparison, the cake layer was composed of inter-connected flakes which were favorable for water passing through during filtration. In many of the conditions tested, a combined fouling layer was formed consisting of both cake and gel substructures.

Swimming has become a popular exercising and recreational activity in China but little is known about the disinfection by-products (DBPs) concentration levels in the pools. This study was conducted as a survey of the DBPs in China swimming pools, and to establish the correlations between the DBP concentrations and the pool water quality parameters. A total of 14 public indoor and outdoor pools in Beijing were included in the survey. Results showed that the median concentrations for total trihalomethanes (TTHM), nine haloacetic acids (HAA9), chloral hydrate (CH), four haloacetonitriles (HAN4), 1,1-dichloropropanone, 1,1,1-trichloropropanone and trichloronitromethane were 33.8, 109.1, 30.1, 3.2, 0.3, 0.6 μg·L−1 and below detection limit, respectively. The TTHM and HAA9 levels were in the same magnitude of that in many regions of the world. The levels of CH and nitrogenous DBPs were greatly higher than and were comparable to that in typical drinking water, respectively. Disinfection by chlorine dioxide or trichloroisocyanuric acid could substantially lower the DBP levels. The outdoor pools had higher TTHM and HAA9 levels, but lower trihaloacetic acids (THAA) levels than the indoor pools. The TTHM and HAA9 concentrations could be moderately correlated with the free chlorine and total chlorine residuals but not with the total organic carbon (TOC) contents. When the DBP concentration levels from other survey studies were also included for statistical analysis, a good correlation could be established between the TTHM levels and the TOC concentration. The influence of chlorine residual on DBP levels could also be significant.

Nanoparticle embedded polysulfone ultrafiltration (UF) membranes were prepared by using the in situ embedment method, and the anti-biofouling properties of the prepared membranes were evaluated by conducting bacteria adhesion test, bacterium inactivation test and biofilm formation test separately. Among the several aluminum and/or silicon oxide nanoparticles tested, alumina (Al2O3) and Linda type L (LTL) zeolite nanoparticles were successfully embedded which could be evenly dispersed on membrane surface with high coverage ratio (38% and 49%, respectively) and were resistant to hydraulic shear detachment. The water contact angles for the nanoparticle embedded membranes (UF-Al2O3 and UF-LTL) and the control membrane (UF-C) were 57°, 40° and 66°, respectively. Owing to the higher surface hydrophilicity, both UF-Al2O3 and UF-LTL demonstrated a higher filterability than UF-C. Biofouling was inhibited on both UF-Al2O3 and UF-LTL, indicated by the lower Pseudomonas aeruginosa biofilm formation rate. Further investigation showed that both UF-Al2O3 and UF-LTL exhibited a high anti-adhesion efficiency to both Escherichia coli and P. aeruginosa, but no bacteriocidal effect on E. coli. The anti-biofouling ability of UF-Al2O3 and UF-LTL mainly benefited from the anti-adhesion ability attributed to the embedded nanoparticles. The improved anti-adhesion ability could not be simply explained by the enhanced hydrophilicity.