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The unique layered structure and abundant 2D nanochannels of MXene membranes have demonstrated outstanding permeability, indicating their great potential in the field of water treatment. However, their unstable interlayer spacing and irregular layer structure have limited their ability to separate small molecular pollutants effectively. In this study, we successfully prepared composite MXene membranes with high rejection and low adsorption properties by exploiting the differences in the surface functional groups and chain lengths of dopamine (DA) and polyethylene glycol (PEG) through an optimal cross-linking approach. These composite membranes exhibited excellent stability in terms of interlayer spacing and mitigated the adverse effects of stacking defects. Compared to MXene membranes, the composite membranes achieved a 1.76-fold increase in dye rejection efficiency, reaching 98.7% at most, with an adsorption ratio of only 1.8%. Moreover, outstanding performances were also exhibited in pressure and concentration load tests. Furthermore, in the context of forward osmosis applications, the composite membranes demonstrated excellent Na+ rejection of 99.9%. More importantly, these membranes showed no performance deterioration throughout 50 filtration cycles, with only a slight increase in permeance of 19.3% over a 38-day testing period. Thus, this work presents a novel solution for fabricating MXene composite membranes with low swelling, minimal defects, and high stability, enhancing its potential in the field of water and wastewater treatment. [Display omitted] • Innovative cross-linking method effectively solved swelling and stacking defects. • High rejection and flux with low adsorption were achieved for DA/PEG@MXene. • Long-term stability and pressure resistance in filtration was further enhanced. [ABSTRACT FROM AUTHOR]

Humic acid (HA) is particularly important in iron-bearing mineral transformations and erosion at the water-mineral boundary zone of the Earth. In this study, three stages of the possible pathway by which HA causes mineral transformation from siderite to goethite are identified. Firstly, a Fe(II)-HA complex is formed by chelation, which accelerates the dissolution and oxidation of Fe(II) from the surface of siderite. As the Fe(II)-HA complex retains Fe atoms in close proximity of each other, ferrihydrite is formed by the agglomeration and crystallization. Finally, the ferrihydrite structurally rearranges upon attachment to the surface of goethite crystals and merges with its structure. The influence of low concentrations of HA (0–2 mg/L) on phosphate adsorption is found to be beneficial by the inducing of new mineral phases. We believe that these results provide a greater understanding of the impact of HA in the biogeochemical cycle of phosphate, mineral transformation. The biochemical phosphate cycle is dependent on interfacial reactions between humic acid and iron-bearing minerals, but the role of humic acid remains unclear. Here the authors study the reaction of siderite with humic acid and its influence on phosphate adsorption. [ABSTRACT FROM AUTHOR]

Abstract Although conventional coagulation pre-treatment can mitigate the fouling of ultrafiltration (UF) membrane when treating raw waters, it is insufficient to restrict the development of irreversible fouling and reversible fouling to a low level. In this paper we demonstrate that the intermittent addition of H 2 O 2 into the membrane tank during backwash events (after coagulation pre-treatment) successfully prevented the development of any significant membrane fouling. Laboratory-scale tests were undertaken using two membrane systems operated in parallel over 60 days, one serving as a reference coagulation-ultrafiltration (CUF) process, and the other receiving the H 2 O 2 (CUF-H 2 O 2), with a decreasing dose in three successive phases: 10, 5 and 2 mg/L. The results showed that the addition of H 2 O 2 (via a separate dosing tube) during a 1 min backwash process (at 30 min intervals) reduced the growth of bacteria in the membrane tank, and the associated concentrations of soluble microbial products (SMP, including protein and polysaccharide). This resulted in a much reduced cake layer, which contained significantly less high MW organic matter (>50%), such as EPS, thereby improving the interaction between particles in the cake layer and/or particles and the membrane surface. There was also less organic matter, of all MW fractions, adsorbed in the membrane pores of the CUF-H 2 O 2 system. The addition of H 2 O 2 in the membrane tank appeared to alter the nature of the organic matter with a conversion of hydrophobic to hydrophilic fractions, which induced less organics adsorption within the hydrophobic PVDF membrane pores, and a reduced bonding ability for particles. There was no physico-chemical evidence of any deterioration of the membrane from exposure to H 2 O 2 , which indicates the feasibility of applying this novel method of fouling control for full-scale UF based water treatment processes. Graphical abstract Image 1 Highlights • The intermittent addition of H 2 O 2 into the membrane tank prevented membrane fouling. • Addition of H 2 O 2 reduced the growth of bacteria and SMP/EPS in the membrane tank. • Cake layer with less EPS decreased the interaction between cake layer and membrane. • The addition of H 2 O 2 alter the nature of organic matter in the membrane tank. • No physico-chemical evidence of any deterioration of membrane by low dose of H 2 O 2. [ABSTRACT FROM AUTHOR]

Drinking water supply in rural areas remains a substantial challenge due to complex natural, technical and economic conditions. To provide safe and affordable drinking water to all, as targeted in the UN Sustainable Development Goals (2030 Agenda), low-cost, efficient water treatment processes suitable for rural areas need to be developed. In this study, a bubbleless aeration BAC (termed ABAC) process is proposed and evaluated, involving the incorporation of a hollow fiber membrane (HFM) assembly within a slow-rate BAC filter, to provide dissolved oxygen (DO) throughout the BAC filter and an increased DOM removal efficiency. The results showed that after a 210-day period of operation, the ABAC increased the DOC removal by 54%, and decreased the disinfection byproduct formation potential (DBPFP) by 41%, compared to a comparable BAC filter without aeration (termed NBAC). The elevated DO (> 4 mg/L) not only reduced secreted extracellular polymer, but also modified the microbial community with a stronger degradation ability. The HFM-based aeration showed comparable performance to 3 mg/L pre-ozonation, and the DOC removal efficiency was four times greater than that of a conventional coagulation process. The proposed ABAC treatment, with its various advantages (e.g., high stability, avoidance of chemicals, ease of operation and maintenance), is well-suited to be integrated as a prefabricated device, for decentralized drinking water systems in rural areas. [Display omitted] [ABSTRACT FROM AUTHOR]

Quantitative methods which link molecular descriptors for recognized precursors to formation of drinking water disinfection byproducts are scarce. This study aimed to develop a simple mathematical tool for predicting chloroform (trichloromethane) yields resulting from aqueous chlorination of model organic precursors. Experimental chloroform yields from 211 precursors were collated from 22 literature studies from 1977 onwards. Nineteen descriptors, some established and others developed during this study, were used as inputs in a multiple linear regression model. The final model, calibrated using five-way leave-many-out cross-validation, contains three descriptors. Two novel empirical descriptors, which quantify the impact of adjacent substituents on aromatic and enolizable chlorine substitution sites, were the most significant. The model has r 2 = 0.91 and a standard error of 8.93% mol/mol. Experimental validation, using 10 previously untested precursors, showed a mean discrepancy of 5.3% mol/mol between experimental and predicted chloroform yields. The model gives insight to the influence that specific functional groups, including hydroxyl, chlorine and carboxyl, have on chloroform formation and the relative contributions made by separate substitution sites in the same molecule. It is anticipated that the detailed approach can be updated and extended as new experimental data emerges, to encompass additional precursors and groups of disinfection byproducts. [ABSTRACT FROM AUTHOR]

This study considers the potential advantages of applying intermittent ultrasound to the ultrafiltration (UF) process to control long term membrane fouling in the context of water treatment. By means of parallel, bench-scale tests using traditional coagulation pre-treatment prior to UF, and intermittent ultrasound during the operation (3 min/10 min every 3 days), the development of fouling material, and its nature (e.g. hydrophilic and hydrophobic), within the cake layer and membrane pores, have been evaluated in detail. In particular, the impact of intermittent ultrasound on bacteria growth and the production of extracellular polymeric substances (EPS) have been investigated. The results have shown that, compared to a control UF process, intermittent ultrasound reduces both reversible and irreversible fouling, with a 50% reduction in transmembrane pressure development over 60 days of operation. The intermittent ultrasound led to a much thinner cake layer which contained less EPS/biopolymers in the form of polysaccharides (g/g) and protein, as well as DNA concentrations. Material removed from the UF membrane by ultrasound was predominantly of high molecular weight (~100 kDa) and hydrophilic in nature. Compared to the control membrane, pore deposits in the membrane receiving intermittent ultrasound contained much less high molecular weight, biopolymer-type substances, which was consistent with the reduced extent of irreversible fouling observed. [ABSTRACT FROM AUTHOR]

The development of a detection method for fluoride and chromium (III) ions using a PET membrane with multiple biomimetic nanochannels is descibed. An asymmetric chemical etching technique was used to create conical nanochannels with a PET (polyethylene terephthalate) nuclear track membrane. SEM images showed that the pore diameter of the tip and base sides of the nanochannel were ∼40 nm and ∼180 nm, respectively. The compounds (4-aminophenyl) boronic acid (APBA) and 5-amino-2-nitrobenzoic acid (ANBA), with a specific recognition for F− and Cr3+ respectively, were modified by a conventional method with EDC and NHS. The current-voltage (I–V) curves of the modified PET membranes in response to the target ions at different concentrations were measured with a picoammeter. Excellent linear relationships between the current value of the I–V curve at −2 V and the concentration of Cr3+ and F− were established to obtain standard detection curves for Cr3+ and F−. From these relationships unknown concentrations of Cr3+ and F− can be quantitatively detected, and the results showed that the detection limits of Cr3+ and F− were as low as 4.10 nM and 0.46 nM, respectively. The performance of the novel method was compared to conventional ICP-MS analysis by the determination of Cr3+ in tap water and samples of the Jing Mi diversion canal, and good agreement was found between the two methods. The accuracy and reliability of the method has demonstrated its potential applicability to a wide range of other ionic contaminants. [Display omitted] • A detection method for ions was established based on the conical nanochannels. • The nanochannels has good recognition, selectivity and stability for F− or Cr3+. • The detection limits F− and Cr3+ were as low as 0.46 nM and 4.10 nM, respectively. • The detection performance of this method for Cr3+ was comparable to that of ICP-MS. [ABSTRACT FROM AUTHOR]

• Slightly elevated phosphorus led to severe membrane biofouling. • No evident changes were observed due to slight concentration elevation of nitrogen. • Thickened fouling layer by phosphorus exhibited better fluorescent organics removal. • Slightly elevated nutrients altered biofilm bacterial, algal, and protozoan communities. Membrane biofouling has been intensively investigated over many years; however, little attention has been paid to the role of slightly elevated nutrients in the fouling formation, especially during drinking water treatment. In this study, we evaluated the respective contribution of slightly elevated nitrogen (ca. 0.5 mg·L−1) and phosphorus (ca. 0.1 mg·L−1) concentrations to membrane biofouling formation and deciphered the associated mechanisms. The results demonstrated that the slight concentration elevation of nitrogen did not substantially decrease the permeate flux, but approximately 50% of the permeate flux was reduced by the elevated phosphorus. The fouling layer was thickened about 4–fold due to the slight elevation of phosphorus and this resulted in the best removal performance of fluorescent organics. In contrast, the fouling layer structure was not markedly changed by the elevated nitrogen. The concentrations of proteins and polysaccharides in the fouling layers increased to different degrees, with phosphorus playing a more pronounced role than nitrogen. The molecular experiments revealed that the filamentous Arthronema dominated the nitrogen–enriched fouling layer, but they decreased to nearly zero in the phosphorus–enriched fouling layer, and the Xanthobacter , which was capable of secreting large amounts of EPS, was enhanced. The growth of algae Chlorellales was stimulated by the elevated nitrogen, while Sphaeropleales was dominant with elevated phosphorus, and for protozoa, Vannella was increased by nitrogen, whereas members of Hartmannella were enhanced by phosphorus. Our findings indicate that the impact of slight increases in concentration of nutrients, especially phosphorus, should be taken into account in drinking water treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

Coagulation prior to ultrafiltration (UF) is widely applied for treating contaminated surface water sources for potable supply. While beneficial, coagulation alone is unable to control membrane fouling effectively in many cases, and there is continuing interest in the use of additional, complementary methods such as oxidation in the pre-treatment of raw water prior to UF. In this study, the application of ozone at low dose in the membrane tank immediately following coagulation has been evaluated at laboratory-scale employing model raw water. In parallel tests with and without the application of ozone, the impact of applied ozone doses of 0.5 mg L −1 and 1.5 mg L −1 (approximately 0.18 mg L −1 and 0.54 mg L −1 consumed ozone, respectively) on the increase of trans -membrane pressure (TMP) was evaluated and correlated with the quantity and nature of membrane deposits, both as a cake layer and within membrane pores. The results showed that a dose of 0.5 mgO 3 L −1 gave a membrane fouling rate that was substantially lower than without ozone addition, while a dose of 1.5 mgO 3 L −1 was able to prevent fouling effects significantly (no increase in TMP). Ozone was found to decrease the concentration of bacteria ( especially the concentration of bacteria per suspended solid ) in the membrane tank, and to alter the nature of dissolved organic matter by increasing the proportion of hydrophilic substances. Ozone decreased the concentration of extracellular polymeric substances (EPS), such as polysaccharides and proteins, in the membrane cake layer; the reduced EPS and bacterial concentrations resulted in a much thinner cake layer, although the suspended solids concentration was much higher in the ozone added membrane tank. Ozone also decreased the accumulation and hydrophobicity of organic matter within the membrane pores, leading to minimal irreversible fouling. Therefore, the application of low-dose ozone within the UF membrane tank is a potentially important approach for fully mitigating membrane fouling. [ABSTRACT FROM AUTHOR]

This paper concerns a previously unreported mechanism of membrane ultrafiltration (UF) fouling when a UF process with coagulation pre-treatment is used in drinking water treatment. The significance of settled coagulant solids (sludge) with different age within the membrane tank on UF fouling has been investigated at laboratory-scale, using model micro-polluted surface water. The process of floc crystallization and increasing bacterial EPS with solids (sludge) retention time may be detrimental to UF operation by causing an increased rate of membrane fouling. In this study the performance of two alum pre-treated hollow-fibre UF units, operated in parallel but with different settled sludge retention times (1 and 7 days), was compared. The results showed that over 34 days of operation the extent of reversible and irreversible fouling was much greater for the 7-day solids retention time. This was attributed to the greater extent of bacterial activity and the presence of Al-nanoparticles, arising from sludge crystallization, at the longer retention time. In particular, greater quantities of organic matter, particularly EPS (proteins and polysaccharides), were found in the UF cake layer and pores for the 7-day retention time. The addition of chlorine later in the membrane run substantially reduced the rate of membrane fouling for both sludge retention times, and this corresponded to reduced quantities of organic substances, including EPS, in the cake layer and pores of both membranes. The results suggest that bacterial activity (and EPS production) is more important than the production of Al-nanoparticles from solids crystallization in causing membrane fouling. However, it is likely that both phenomena are interactive and possibly synergistic. [ABSTRACT FROM AUTHOR]

The accumulation of residual coagulant flocs and microbial substances on the surface of ultrafiltration (UF) membranes are major contributors to membrane fouling that reduces process performance. Previous approaches to reduce fouling (e.g. addition of an oxidant or disinfectant) have been only partly successful in reducing the formation of a cake layer and material deposits within membrane pores. In this study the performance of an integrated granular media – UF membrane process has been evaluated in which a hollow-fibre UF module was embedded within a sand layer in order to prevent fouling material reaching the UF surface (forming a cake layer). The evaluation involved comparing two laboratory-scale UF systems, operated in parallel for 74 days, with one incorporating the sand layer (CSUF, coagulation-sand layer filtration-ultrafiltration), and the other without (CUF, coagulation-ultrafiltration), serving as a reference conventional process. The results showed that the incorporation of the sand layer successfully prevented the formation of any significant cake layer on the membrane surface and substantially reduced inner membrane fouling, which lead to a much reduced trans-membrane pressure (TMP) increasing rate. The difference in performance was principally attributed to microbial growth and the release of extracellular polymeric substances (EPS) which was much greater in the conventional CUF system. Thus, in the CUF system, the deposition of coagulation flocs (consisting of precipitated nano-scale primary particles) and bacteria on, and within, the membrane produced substantial reversible and irreversible fouling. In contrast, the deposited material (flocs) in the sand layer of the CSUF system was easy to be washed away, resulting in fewer bacteria in the sand layer, and a much reduced production of biopolymer and other EPS, and their accumulation by the UF membrane. [ABSTRACT FROM AUTHOR]

Due to their susceptibility to oxidation and swelling in water, MXene membranes are difficult to prepare with sufficient stability to be effective in water treatment applications. In addition, MXene membranes display deleterious adsorption effects and methods of preventing adsorption have not been developed adequately yet. In this paper, we describe the preparation of an enhanced membrane by incorporating ascorbic acid into the main body of Ti 3 C 2 T X -MXene, and aluminum ion cross-linking of membrane layers. Both ex-situ experimental characterization and density functional theory (DFT) simulations have verified the strong adsorption force between MXene and ascorbic acid. Under the action of cross-linking aluminum ions, the anti-swelling property of the membrane was greatly improved. As a result of the modifications, the membrane exhibited a retention rate of 99.3% for a representative dye, of which the contribution of adsorption was only 7.9%. In addition, the membrane was also able to effectively inhibit the transmembrane transport of sodium chloride and magnesium chloride during forward osmosis. The penetration rate of sodium chloride in 1 h was only 0.065%. More importantly, thanks to the enhanced antioxidant properties, there was no sign of oxidation in the 30-day experiment. While maintaining structural stability, the membrane had a flux that was 30 times that of a comparative graphene oxide membrane. The findings represent an important step forward in the development of a stable, high performance and low-adsorption Ti 3 C 2 T x -MXene membrane. [Display omitted] • Ti 3 C 2 T X -MXene membrane crosslinked by ascorbic acid and Al3+were prepared. • The membrane of high stability was no sign of oxidation in the seven-day experiment. • The membrane had a flux that was 30 times that of a comparative GO membrane. • The membrane exhibited a retention rate of 99.25% with only 7.94% adsorption. • The penetration rate of NaCl in 1 h was only 0.065% during forward osmosis. [ABSTRACT FROM AUTHOR]

• Effects of various MW NOM on DBPFP and DBPs in the NF-treated water were investigated. • The medium molecular weight NOM protected NF from fouling. • The medium molecular weight NOM reduced the DBPFP or DBPs in the NF treated water. • The medium molecular weight NOM works through forming a layer on the NF membrane. Nanofiltration (NF) is utilized in water treatment for controlling disinfection by-products formation potential (DBPFP) and disinfection by-products (DBPs). Attention regarding NF-based technology has been paid on membrane fouling of NF and the rejection efficiency of contaminants by NF membranes. Natural organic matter (NOM) presenting in surface waters is one main removal target in drinking water treatment by NF-based technology, and is thereby a contributor to the membrane fouling of NF. In application, pretreatments of other membrane filtration (e.g., microfiltration (MF) and ultrafiltration (UF)) has been taken prior to NF, resulting in the separation of NOM of specific molecular weight. Meanwhile, it is well known that NOM is composed of organic compounds of different molecular weights. However, the effect of NOM of specific molecular weight has been seldom investigated from the aspects of membrane fouling and the resulting DBPFP after membrane filtration. By using combinations of MF and UF (molecular weight cut-off of 100K or 20K) as pretreatment prior to NF, the NOM of various molecular weight on DBPFP and DBPs in the NF-treated water were investigated. The experiments were conducted with two real-world surface water samples and one tap water sample. It was found that medium molecular weight NOM, defined as NOM that passed UF100K but did not pass UF20K in this study, reduced fouling of the NF membrane. This is supported by the excitation and emission matrix (EEM) fluorescence spectra, size exclusion chromatography (SEC) and flux analysis. In addition, the medium molecular weight NOM also reduced the DBPFP in the NF treated water and eventually the DBPs by participating in forming a protective layer on the NF surface, blocking the transfer of small molecular weight NOM into the NF filtrate, thereby reducing the DBPFP of the NF filtrate since small molecular weight NOM was the major contributor to DBPFP in this study. [ABSTRACT FROM AUTHOR]

This article summarizes a preliminary investigation of the treatment of humic acid (HA) in drinking water by a novel combination of potassium manganate, ferrous sulfate, and magnetic ion exchange (MIEX) resin. Manganate (MnO42−) is a stronger oxidant than permanganate, which has received little attention to date as a water treatment chemical, but in combination with ferrous sulfate (FeMnO) can offer a potentially advantageous and more economical means of achieving preoxidation objectives and in-situ coagulation by Fe(III) species. To enhance removal of organic substances, particularly low-molecular-weight and more hydrophilic compounds, subsequent treatment by MIEX was included as part of the overall process. Using model HA solutions of 5 mg/L dissolved organic carbon (DOC), a solution pH of 6.5, and a constant Fe:Mn molar ratio (2:1), the optimal FeMnO dose for organics (DOC) removal was 0.06 mM (as K2MnO4). At this optimal dose, and with 10 mL/L of MIEX, the DOC remaining after treatment was only 0.4 mg/L, representing an overall organics removal of 92%. Synchronous fluorescence spectra of solutions during the treatment stages showed a corresponding major reduction in fluorophore peaks with a near complete removal of fluorophore compounds in the ranges, 360 nm<λex<420 nm and λex>420 nm. [ABSTRACT FROM AUTHOR]

This paper describes some results of mini-pilot-scale tests concerning the performance of potassium manganate (K 2 MnO 4 ) as a pre-treatment chemical prior to ultrafiltration. Manganate is an intermediate in the commercial preparation of permanganate and in aqueous reactions MnO 4 2− can act as both an oxidant and a coagulant/adsorbent arising from the formation of insoluble MnO 2 . In addition, the combination of ferrous sulfate and manganate (Fe/Mn), offers a potentially cheaper and effective combination of pre-oxidant and coagulant compared to the chemicals used currently in water treatment (e.g. ozone, chlorine, ferric sulfate). In comparative tests with conventional ferric sulfate and using simulated raw water, the results showed that Fe/Mn pre-treatment substantially reduced membrane fouling in terms of the rate of trans-membrane pressure development (arising from both external and internal fouling). Fe/Mn pre-treatment was effective in reducing bacterial activity, changing the characteristics of organic matter and decreasing the production of extracellular polymeric substances (EPS) by bacteria. The external fouling in this process was determined by the EPS concentration, and the internal fouling mainly determined by the adsorption of lower MW organic matter to the membrane pores. Fe/Mn pre-treatment reduced the amounts of both types of fouling material within the cake layer and membrane pores in comparison to conventional pre-treatment with ferrous sulfate, most likely through the formation of solid-phase Fe(III) and MnO 2 and by MnO 4 2− oxidation, thereby leading to a substantial increase in membrane run time. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) graphene oxide (GO) membranes continue to attract interest due to their superior permeation and separation performance, and are regarded as a promising technology for water purification. However, the imperfect interlayer microstructure under the applied hydraulic pressure, and the inferior stability are still considerable challenges to achieve high permeability, selectivity and operability. In this paper, we describe for the first time, the development and testing of a dual-site supported GO membrane (SEN-Mg/GO) by introducing biuret (SEN) and Mg2+ inside the interlayer structure. SEN can support the GO sheets in the oxide sites based on a condensation reaction between amino and carboxyl groups, while Mg2+ is fixed in the graphitic sites through a non-covalent cation-π interaction. A synergistic effect of the dual-site crosslinking and support build more favorable nanochannels for the rapid transport of water while also imparting the membrane to maintain a tightly-packed 2D structure, which increases water flux without sacrificing the separation performance. In comparison, SEN-Mg/GO exhibited a water flux 4 times greater than the GO and SEN only cross-linked GO membrane (SEN/GO), with high selectivity towards various model dye molecules (>98%). The SEN-Mg/GO membrane also achieved greater "trade-off" between flux and rejection and significantly improved stability than the Mg2+ only cross-linked GO membranes (Mg/GO). The optimized nanochannels and the interlayer covalent bond are considered to be the dominant factors in improving the separation performance and stability of the membrane, respectively. The dual-site supporting technique provides a new approach for the fabrication of GO membranes of high performance, and can be used in the design of other 2D lamellar membranes. [Display omitted] • Novel SEN-Mg/GO membranes fabricated by dual-site support approach. • Dual-site support approach suppresses shrinkage and collapse of interlayer nanochannels. • SEN-Mg/GO membrane had 4-fold greater water flux and comparable rejection compared with SEN/GO membrane. • SEN-Mg/GO membrane has long term stability over a wide range of pH. [ABSTRACT FROM AUTHOR]

• Low dose oxidant can abate membrane fouling in GDM filtration. • Biopolymers were removed from influent water by dosed oxidants. • Dosed oxidants significantly altered biofilm bacterial community structure. • Formed δ-MnO 2 nanosheets layer protected membrane pore from contamination. Membrane fouling is the principal factor that currently limits the performance of gravity-driven membrane (GDM) filtration systems in drinking water treatment. In this study, the benefits of applying a low dose (approximately 0.1 mg · L − 1 ) of environmentally benign oxidants, both H 2 O 2 and KMnO 4 , as a pretreatment to GDM filtration system has been evaluated in terms of reduced membrane fouling and treated water quality. While both oxidants improved permeate flux, the effect of KMnO 4 was greater than H 2 O 2. Both oxidants reduced the size of influent organic substances and those of large molecular weight (>20 kDa), such as biopolymers, disappeared. The thickness of the fouling layers was substantially reduced after oxidation, and the KMnO 4 system had a markedly different physical structure of fouling layer, with an apparent sub-layer of δ-MnO 2 nanosheets below a fouling sub-layer. The formation of the δ-MnO 2 nanosheets sub-layer appeared to protect the underlying membrane pores from contamination by influent organics. Oxidation pretreatment reduced the presence of proteins and polysaccharides in the fouling layers and significantly altered the bacterial community structures (p < 0.01) and decreased biodiversity. The microbial species that secreted amounts of extracellular polymeric substances (EPS), such as Xanthobacter, were not eliminated in the H 2 O 2 fouling layer, while for the KMnO 4 system, the manganese oxidizing bacteria (MOB; e.g., Pseudoxanthomonas) and metal-resistant genus Acidovorax, dominated the community. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] The increase rate of TMP was greatly higher for the FeCl3–UF system than alum–UF. [•] Smaller primary particles and nano-scale particles were evident in FeCl3–UF system. [•] The lower porosity and greater thickness of the cake layer in FeCl3–UF system. [ABSTRACT FROM AUTHOR]

Biofouling layer (i.e., biofilm) is an inevitable presence for the membrane filtration processes. In this study, we elucidated biofouling formation from the perspective of affecting the attachment of bacteria for the first time, whereby the role of initial available biopolymers was revealed. Results demonstrated that the presence of initial available biopolymers increased the abundance of the genus Caulobacter , which was capable of mineralizing biopolymers; whereas, for the typically oligotrophic species of Polynucleobacter , it exhibited low abundance. Greater concentrations of polysaccharides and proteins were accumulated in the biofouling layer, when provided with initial biopolymers, and the biofilm structure was more heterogeneous with larger pore size and higher thickness. Thereby, the corresponding filtration system exhibited greater permeability and better removal performance of organics. Collectively, the initial available biopolymers altered the attachment conditions for the bacteria, which subsequently impacted the bacterial community, and in turn biofilm composition, physical structure and filtration performance. [Display omitted] • Biofouling was firstly explored from perspective of affecting bacterial attachment. • Presence of initial available biopolymers could alter biofilm bacterial community. • Discrepancy in microbial community differed biofilm composition and structure. • Higher porosity in biofouling layer led to lower hydraulic resistance. [ABSTRACT FROM AUTHOR]

Abstract: The application of in-situ Fe(III) coagulant, formed by reacting Fe(II) and KMnO4 (Fe/Mn), before membrane ultrafiltration (Fe/Mn-CUF) has been compared with conventional dosing of an Fe(III) coagulant (Fe-CUF). The performance of the alternative coagulants has been evaluated in terms of membrane fouling using model waters containing humic acid. A lower development of trans-membrane pressure (TMP) suggested that in-situ formed Fe(III) caused a lower rate of fouling compared to the dosed Fe(III). The lower TMP development with in-situ formed Fe(III), compared to dosed Fe(III), was associated with smaller, fewer and less compact coagulant flocs and differences in the membrane cake layer; in both cases influent flocs were aggregates of nanometer-scale primary particles. Interestingly, TEM and SEM images showed that the size of nanometer-scale particles formed by in-situ Fe(III) was slightly larger than dosed Fe (III), and this contributed to a more porous cake layer. In addition, the Fe/Mn flocs formed a thinner cake layer than that formed by Fe flocs. Overall, the effect of decreasing the thickness and density of the cake layer and increasing the size of the nanometer-sized primary particles was significantly beneficial in reducing membrane fouling. Also NOM analysis by size exclusion chromatography (SEC) indicated that the in-situ Fe(III) coagulant achieved greater NOM removal than the dosed Fe(III), both in the UF influent and filtrate waters. In summary, the results have shown that in-situ Fe(III) is a superior pretreatment to conventional dosed Fe(III), in terms of significantly improving membrane performance (reduced fouling) with a little higher improvement in water quality. [Copyright &y& Elsevier]

Abstract: In metal machining processes, the regulation of heat generation and lubrication at the contact point are achieved by application of a fluid referred to as metalworking fluid (MWF). MWFs inevitably become operationally exhausted with age and intensive use, which leads to compromised properties, thereby necessitating their safe disposal. Disposal of this waste through a biological route is an increasingly attractive option, since it is effective with relatively low energy demands. However, successful biological treatment is challenging since MWFs are chemically complex, and include biocides specifically to retard microbial deterioration whilst the fluids are operational. In this study remediation of the recalcitrant component of a semi-synthetic MWF by a novel hybrid ozone-bacteriological treatment, was investigated. The hybrid treatment proved to be effective and reduced the chemical oxygen demand by 72% (26.9% and 44.9% reduction after ozonation and biological oxidation respectively). Furthermore, a near-complete degradation of three non-biodegradable compounds (viz. benzotriazole, monoethanolamine, triethanolamine), commonly added as biocides and corrosion inhibitors in MWF formulations, under ozonation was observed. [Copyright &y& Elsevier]

Abstract: The aqueous degradation of iopromide, an iodinated X-ray contrast media (ICM) compound, by the combination of UV254 irradiation and potassium peroxydisulfate (K2S2O8) has been studied in laboratory scale experiments. The influence of various parameters on the performance of the treatment process has been considered, namely the UV irradiation light intensity, the initial concentrations of iopromide and peroxydisulfate, and the initial solution pH. Iopromide degradation increased with UV light intensity and peroxydisulfate concentration, but decreased with initial pH. Under specific conditions complete removal of iopromide was achieved within 30min, and near-complete mineralisation (loss of solution TOC) within 80min. Degradation was believed to be caused by a combination of direct photolysis, sulphate radical attack, and, to a minor degree, direct oxidation by peroxydisulfate. Approximate values for the reaction rate constants have been determined and found to be equal to 1–2×104 M−1 s−1 for sulfate radicals, and 1–2M−2 s−1 for S2O8 2−. Overall compound degradation was observed to follow first-order kinetics where the rate constant decreased with initial solution pH. During the reaction, the solution pH decreased as a consequence of sulfate radical scavenging. [Copyright &y& Elsevier]

The influence of natural organic matter on contaminant removal by :Fe0 systems has been of increasing concern. Recent studies have shown that, in addition to direct sorption on the Fe0 surfaces, humic acid complexation with dissolved iron released from corrosion results in the formation of colloids and aggregates in solution that may affect contaminant removal. High-pressure size-exclusion chromatographic analyses revealed increasing molecular weights of dissolved humic acids with reaction time. Humic acid aggregation occurred across a wide range of molecular weight fractions. Fourier transform infrared spectroscopic analysis of humic acid aggregates suggested the presence of inner-sphere complexation involving different oxygen-containing functional groups; hydrophobic interactions also probably contributed to aggregation as the humic acid of more aromatic and hydrophobic character was aggregated at a faster rate. Because of multiple underlying processes, a variety of cross-correlated physicochemical properties of humic acids contributed to their aggregation. The presence of humic acid aggregates provided an additional hydrophobic domain for partitioning that enhanced trichloroethylene removal, although steric blocking of the Fe0 surfaces may inhibit its reduction to some extent. Comparable effects were demonstrated for various types of humic acids. [Copyright &y& Elsevier]

The performance of a new commercial tannin-based cationic polymer (TBP) has been investigated at bench-scale in terms of its capability to coagulate colour and humic material. The TBP is characterised as a moderate-to-high molecular weight polymer (~600,000 gmol-1) with a cationic charge (~3meqg-1) arising from a single tertiary amine group per monomer. The TBP is substantially affected by hydrolysis/hydration processes which lead to changes in its charge density and solubility with solution time and pH. Laboratory experiments were carried out to evaluate the optimal dose, pH and treatment performance of TBP with simulated and real coloured waters. With simulated water TBP was able to achieve a high dissolved organic carbon (DOC) reduction over a wide pH range (4-9), but the optimal dose increased with pH as a consequence of the loss of cationic charge and solubility. At pH 7, the coagulation performance of TBP was comparable to that of alum and polyDADMAC at optimum coagulant doses. With real coloured water, jar and flotation tests showed that the TBP was able to match the performance of a polymeric iron sulphate in terms of treated water colour and turbidity, but residual DOC was significantly higher with TBP. [ABSTRACT FROM AUTHOR]

This study investigates the aqueous degradation of four iodinated x-ray contrast media (ICM) compounds (diatrizoate, iomeprol, iopromide, and iopamidol) by ozone and combined ozone and hydrogen peroxide. In laboratory scale experiments, second-order kinetic rate constants for the reactions of the ICM compounds with molecular ozone and hydroxyl radicals, and overall at pH 7.5, were determined. For the four ICM compounds the degradation rate constants with molecular ozone were low and in the range of 1–20 M-1 s-1, whereas the rate constants with hydroxyl radicals were in the range of 1×109–3×109 M-1 s-1. Diatrizoate had the lowest rate constant of the four compounds with respect to molecular ozone reactions. At pH 7.5, the extent of compound degradation was proportional to the applied ozone dose and inversely related to the initial compound concentration at a given ozone dose. At this pH approximately 90% of the degradation could be attributed to hydroxyl radical reactions. Enhancement of the radical mechanism by the addition of hydrogen peroxide during ozonation led to complete removal of the nonionic compounds, and >80% removal of diatrizoate, at relatively low oxidant mass ratios (H2O2/O3<0.25). A similar enhancement in compound degradation was evident with the presence of small concentrations of humic substances (∼4–5 mg L-1). Ozone oxidation led to major cleavage of the ICM compounds and the release of inorganic iodine; the proportion of iodine release was similar among the nonionic ICM compounds but much greater for diatrizoate. [ABSTRACT FROM AUTHOR]

[Display omitted] • First study of membrane technology to remove impurities from stevia extract. • FeSO 4 forms complexes with organic compounds causing serious membrane fouling. • PAFC can remove impurities more effectively and reduce membrane fouling. • Hydrodynamic flux and trans-membrane current were used to quantify membrane fouling. Stevia sugar is widely used in food owing to its advantages of low calorie content and high sweetness. In the production of stevia sugar, stevia leaves are immersed in water to obtain a crude liquor, which contains many impurities, such as proteins, polysaccharides, organic acids, etc. These impurities are removed typically by coagulation and filtration. At present, suppliers of stevia mainly use a "lime + ferrous sulfate (FeSO 4)" process as the pretreatment, but residual SO 4 2− can cause hydrogen sulfide corrosion and Ca2+ can affect the safety of subsequent boilers in the process. In this study, polyaluminium ferric chloride (PAFC) was evaluated as a superior coagulant to FeSO 4 , together with ultrafiltration (UF) and nanofiltration to remove flocs and other organic contaminants. It was found that coagulation by PAFC out-performed FeSO 4 and was unaffected by pH, while the performance of FeSO 4 was sensitive to pH. At pH 10, FeSO 4 had an enhanced coagulation efficiency, but formed soluble Fe2+ complexes with organic substances in the original solution, which adversely affected the quality of the filtrate. Compared with a UF membrane, the NF membrane was more effective in removing contaminants, and more tolerant to membrane fouling. In addition to hydrodynamic flux, measurement of trans-membrane electrical current were used to reflect the severity of membrane fouling. The combination of PAFC as coagulant without pH adjustment, and ultrafiltration, was found to be a simpler and superior treatment for stevia liquor with a high degree of contaminant separation, and avoidance of problems caused by SO 4 2− and Ca2+. [ABSTRACT FROM AUTHOR]

Abstract: A commercial tannin-based cationic polymer (TBP) has been investigated to establish its basic chemical properties and its coagulation performance in preliminary trials with a model water containing a kaolin suspension. The TBP appears to be a moderate-to-high molecular weight polymer (∼600,000gmol−1), with approximately 1000–2000 repeating units, and a reasonably narrow molecular weight distribution. The cationic nature of the polymer is believed to be a single tertiary amine group per monomer, giving a charge density of approximately 3mequiv.g−1. The TBP is substantially affected by hydrolysis/hydration processes which lead to changes in its charge density and solubility with solution time and pH. The loss of cationic charge (by amine de-protonation) and solubility with pH in the typical pH range for water treatment (i.e. pH 6–9) makes the behaviour of TBP similar to that of conventional aluminium and iron salt coagulants. Laboratory experiments were carried out using a photo-dispersion analyzer (PDA) to evaluate the coagulation performance of TBP at different pH values, and in comparison with alum and polyDADMAC. The results showed that the optimal TBP dose increased with increasing pH, principally because of polymer precipitation, but there was a corresponding increase in coagulation performance. In comparison with alum and polyDADMAC, at optimal doses, the performance of the TBP in treating a kaolin suspension was inferior at neutral pH. However, in higher solution pH conditions the coagulation performance of TBP appears to improve substantially, albeit with a greater dose required, and at pH 9 it was arguably superior to the other two coagulants. [Copyright &y& Elsevier]

The aqueous degradation of iodinated X‐ray contrast media (ICM) by the combination of ozone and ultrasound has been studied. Experiments were conducted at a constant ultrasound frequency of 20 kHz, at five power densities up to 0.235 W/mL, and various ozone centrations. In experiments involving dissolved ozone in solution, the addition of ultrasound significantly decreased the oxidation performance of the dissolved ozone, while the combination of dissolved oxygen and ultrasound gave a greater oxidation performance than ultrasound alone. However, the combination of gaseous ozone and ultrasound was found to give a higher degree of compound degradation than either ozone or ultrasound alone. In the experiments with final effluent, the degradation of ICM compounds by gaseous ozone and ultrasound was found to depend on the ozone dose applied. The degradation of ICM compounds in final effluent was modeled, which was found to moderately overestimate the observed compound degradation. [ABSTRACT FROM AUTHOR]

The aqueous degradation of iodinated X-ray contrast media (ICM) by the combination of ozone and ultrasound has been studied. Experiments were conducted at a constant ultrasound frequency of 20 kHz, at five power densities up to 0.235 W/mL, and various ozone centrations. In experiments involving dissolved ozone in solution, the addition of ultrasound significantly decreased the oxidation performance of the dissolved ozone, while the combination of dissolved oxygen and ultrasound gave a greater oxidation performance than ultrasound alone. However, the combination of gaseous ozone and ultrasound was found to give a higher degree of compound degradation than either ozone or ultrasound alone. In the experiments with final effluent, the degradation of ICM compounds by gaseous ozone and ultrasound was found to depend on the ozone dose applied. The degradation of ICM compounds in final effluent was modeled, which was found to moderately overestimate the observed compound degradation. [ABSTRACT FROM AUTHOR]

The indirect reaction of octylphenol (OP) and nonylphenol (NP) with hydroxyl radicals ( OH) during ozonation was investigated at pH values ranging from 6 to 9. A parameter R ct , representing the ratio of the OH-exposure to the ozone-exposure, was measured using a method involving a low concentration of p-chlorobenzoic acid as a OH-probe compound during the ozonation. By assuming that R ct is a constant value at a given pH, the second order rate constants of the alkylphenol reaction with hydroxyl radicals were determined as 1.4(±0.2)×1010 and 1.1(±0.2)×1010 M−1 s−1 for OP and NP, respectively. The proportions of each alkylphenol degraded by direct molecular ozone reaction and indirect hydroxyl radical reaction were predicted at different pH values. The contribution of indirect OH reactions with each AP was found to represent over 50% of the total degradation for pH≈7, and the contribution increases substantially with pH>7. [Copyright &y& Elsevier]

This aqueous reaction between ozone and two alkylphenols (APs), namely octylphenol (OP) and nonylphenol (NP), has been investigated. Both compounds are important endocrine disrupting chemicals, which arise from the biodegradation of alkylphenol ethoxylates and are often found at relatively high concentrations in wastewater effluents. In this paper the results of an experimental study are presented which provide values for the reaction rate constants between molecular ozone and undissociated OP and NP, and overall reaction rate constants for the degradation of the two APs at pH values in the range of 7–9. The kinetic rate constants for OP and NP degradation by molecular ozone were 4.33(±0.18)×104 and 3.90(±0.10)×104 M−1 s−1, and the reaction stoichiometry was similar in both cases and equal to approximately 1.3:1 ([O3]:[AP]). The overall second order reaction rate constants for the two APs increased significantly with increasing pH, which is believed to be mainly due to the increasing influence of indirect radical reaction with increasing pH; this aspect is considered in more detail in a companion paper. A preliminary investigation of the reaction mechanism suggests that an initial product of ozonation is hydroxyl-alkyl phenol. [Copyright &y& Elsevier]

The presence of endocrine-disrupting compounds (EDCs) in the aqueous environment is of increasing concern due to their adverse impact on aquatic life, and potential risk to human health. Among the EDCs of concern are steroidal estrogenic hormones such as estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethinylestradiol (EE2), which have a high environmental prevalence and strong estrogenic activity. In addition, the extensive use of alkylphenol ethoxylates (APnEOs), bisphenol A (BPA) and phthalate compounds have resulted in an environmental presence at significant concentrations, although they appear to have a lower estrogenic activity than the steroidal hormones. As water and wastewaters are some of the primary routes of exposure to EDCs, it is important to determine at what levels EDCs are found in these media and how these levels may be reduced. Hence, it is necessary to understand the fate of EDCs in conventional water and wastewater treatment plants, as well as the efficacy of more specialized treatment methods, such as adsorption and oxidation. This paper is a summary of the latest information on the degradation of prominent EDCs by ozone and ozone-based advanced oxidation processes (AOPs). From this review, it is clear that ozone and AOPs are effective in degrading these EDCs, with the possible exception of phthalates, which are relatively stable to ozone oxidation. Knowledge of the formation of reaction products from the treatment by ozone and AOPs is relatively poor at present, and particularly for the non-steroid compounds. [ABSTRACT FROM AUTHOR]

This paper presents information concerning the influence of solution pH on the aqueous reaction between potassium ferrate and phenol and three chlorinated phenols: 4-chlorophenol (CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP). The redox potential and aqueous stability of the ferrate ion, and the reactivity of dissociating compounds, are known to be pH dependent. Laboratory tests have been undertaken over a wide range of pH (5.8–11) and reactant concentrations (ferrate:compound molar ratios of 1:1 to 8:1). The reactivity of trichloroethylene was also investigated as a reference compound owing to its non-dissociating nature. The extent of compound degradation by ferrate was found to be highly pH dependent, and the optimal pH (maximum degradation) decreased in the order: phenol/CP, DCP, TCP; at the optimal pH the degree of degradation of these compounds was similar. The results indicate that for the group of phenol and chlorophenols studied, the presence of an increasing number of chlorine substituent atoms corresponds to an increasing reactivity of the undissociated compound, and a decreasing reactivity of the dissociated compound. [Copyright &y& Elsevier]

An optimal prepolymerized inorganic coagulant, poly-alumino-iron sulphate (PAFS), was developed and examined for drinking water treatment. PAFS is a new type of prehydrolyzed metal-ion coagulant. An investigation of the conditions for preparing (PAFS has been conducted using Al[SUB2](SO[SUB4])[SUB3] with Fe[SUB2](SO[SUB4])[SUB3] as primary raw materials. Optimization of the preparation conditions of the PAFS involved variation of the total metal-ion concentration, oxidation temperature, the molar ratio of the oxidant to metal-ion, and the oxidation period. An evaluation of the coagulation performance with two types of test waters showed that selected PAFS coagulants achieved either a greater or similar removal in terms of percentages of color, (UV)(254 nm) (absorbance and dissolved organic carbon in)comparison with another polymeric coagulant, polyferric sulphate (PFS). However, both of these (PAFS and PFS) had a superior performance to ferric sulphate (FS) and aluminum sulphate (AS). Of particular significance was that PAFS achieved the lowest residual metal-ion concentrations, Fe and Al, in comparison with PFS, FS, and AS, respectively. [ABSTRACT FROM AUTHOR]

Ozone is known to enhance the removal of particles in coagulation-filtration systems under certain circumstances. In this work it was observed that bicarbonate is required in order for ozone, applied prior to coagulant addition, to have a beneficial effect on coagulation-filtration and that, in the absence of bicarbonate, ozone has a detrimental effect. It is hypothesized that ozone acts in a positive manner via direct molecular reactions and in a negative manner by the hydroxyl radical pathway, with bicarbonate serving as a hydroxyl radical scavenger. [ABSTRACT FROM AUTHOR]

The aqueous reactivity of 2,4,6-trichlorophenol (TCP) with ozone has been studied at laboratory-scale using a simple gas bubble/liquid contacting system. Degradation rate constants were measured directly and found to be 7.6 and 77.2 M−1 s−1 at pH 2 and 7.5, respectively. At pH 7.5, 10 min of ozonation (≡15 mM ozone consumption) achieved a 90% degradation of TCP, which corresponded to the release of approximately 2 mol Cl− per mol TCP. The presence of hydrogen peroxide in solution did not significantly increase the TCP degradation but increased the overall dechlorination to 2.7 mol Cl− per mol TCP. The presence of humic acid (HA) in solution was found to enhance the degradation rate of TCP at low relative HA concentrations (<0.6 g/g HA:TCP), but to reduce the rate at higher HA concentrations. [Copyright &y& Elsevier]

Presents a laboratory study of electro-coagulation-flotation for water treatment. Key issues of interest; Analysis of pertinent topics and relevant issues; Implications on water research.

A novel process involving the simultaneous electrochemical-oxidation (EO) and electrosynthesis of ferrate has been investigated for the treatment of the commonly detected and recalcitrant pesticide, atrazine. The present study considered the electrosynthesis of ferrate, in neutral pH, using low concentration iron (Fe2+) representative of raw water levels and its subsequent effect on atrazine degradation. Ferrate synthesis was unaffected by current density (10–80 mA cm−2), indicating mass transport limitations. Synthesis was affected by the initial iron concentration, whereby 0.051, 0.108 and 0.332 mg L−1 was generated with an Fe2+ concentration of 0.5, 1.0 and 3.0 mg L−1, respectively. When operating under simultaneous EO and ferrate oxidation, atrazine degradation exceeded that of a solely EO process. From an initial concentration of 2.00 mg L−1, atrazine was degraded to 1.34, 1.05 and 0.51 mg L−1 during 10, 40 and 80 mA cm−2, characterised by pseudo-first-order kinetics. Degradation with electrochemically-generated ferrate could be described by second-order kinetics, and yielded a degradation rate constant of 23.5 M−1 s−1. The effect of natural organic matter (NOM) on atrazine degradation was also investigated. Ferrate was observed to be mostly scavenged by resorcinol, a representative NOM compound, having a second-order reaction rate constant of 9.71 × 102 M−1 s−1. [Display omitted] • Novel example of in-situ ferrate production in neutral pH conditions, using ambient iron (Fe2+). • Electro-oxidation and ferrate electro-generation process employed for atrazine degradation. • Electrochemical atrazine degradation significantly increased with ferrate production. • Atrazine degradation pathway proposed for electro- and ferrate oxidation processes. • Effect of a dissolved organic scavenger (resorcinol) on atrazine oxidation evaluated. [ABSTRACT FROM AUTHOR]

• Study the mechanism of the inaccurate in the NOM UVP-TOC detection. • Intramolecular and intermolecular aggregation can cause inaccuracy. • Foaming during the IC purging process can cause inaccuracy. • Hydrolysis, pre-oxidation and adding defoamer can improve accuracy. The UV-persulfate oxidation method is widely used for determining the total organic carbon concentration of aqueous samples (denoted for convenience as UVP-TOC). However, for some surface water samples, the measurement of TOC by this method can be unreliable, deviating significantly from the true carbon content. In this study, the performance of the UVP-TOC method has been investigated by comparing the results from the analysis of a variety of aqueous samples that included two kinds of surface water samples and related surface water model substances: bovine serum albumin (BSA), sodium alginate (SA), humic acid (HA), tannic acid (TA), benzoic acid (BA) and citric acid (CA), with those from a high-temperature combustion method (elemental analysis); the latter providing the true carbon content value. By comparing the above data, it was found that the UVP-TOC method significantly underestimated the TOC value of the surface water samples, and it was also found that the model components BSA (protein) and HA (humic substances, HS) had a substantial influence on the TOC underestimation, while the SA (polysaccharide), TA (complex organic molecule) and CA/BA (small molecules) had little effect. The results showed that the agglomeration within and between BSA and HA molecules was an important reason for the inaccurate UVP-TOC values of BSA and HA. A further limitation was that for BSA, surfactants (e.g. sodium dodecylbenzene sulfonate, SDBS) and other surfactant-like substances, foam was formed during the CO 2 removal purging process by N 2 that seriously interfered with the determination of TOC. The study provides new information and insight into the causes of inaccuracies in the UVP-TOC analysis of surface waters and possible approaches to improve the accuracy. [Display omitted] [ABSTRACT FROM AUTHOR]

• The MWs of NOM greatly influence the DBC removal during coagulation. • The DBC removal was promoted by the presence of NOM in water. • The DBC removal was promoted by the NOM with low MW adsorbed on it. • There was a decrease in aggregation of the DBC with increasing MW of NOM. Black carbon is a ubiquitous contaminant that is widely present in water sources, where, as dissolved (<0.2-µm) black carbon (DBC), it contributes to the pool of disinfection byproduct precursors. DBC, in the form of nano-scale particles, provides a large surface area to adsorb natural organic matter (NOM) and while NOM with large molecular weight (MW) is readily removed by coagulation, it is unclear whether the presence of different MW fractions of NOM adsorbed on DBC improves or impairs its removal. In this study, experiments have been conducted to investigate the interactions between DBC with different NOM MW fractions, and alum coagulant. The results found that as the MW of NOM decreased, the total organic carbon of adsorbed NOM on the DBC nanoparticles (NPs) decreased, whereas the DBC removal increased due to the increased destabilization of DBC NPs. As the MW of NOM decreased, the size of DBC with adsorbed NOM decreased, whereas the size of its flocs increased. As the MW of NOM decreased, the variation of carbon to oxygen ratio decreased, indicating the aggregation degree of DBC adsorbed with NOM increased. It was observed that as the MW of adsorbed NOM increased, there was a decrease in aggregation of the DBC, as well as the amount of aggregated DBC NPs detected in the flocs. The findings of this study provide important new information concerning the mutual interaction between NOM and DBC NPs and the effect of NOM on the fate of DBC during underground water treatment. [ABSTRACT FROM AUTHOR]

• The effect of anions is determined by their affinity to Al3+, concentration and pH. • Chloride ions had no significant effect on coagulation. • Sulphate decreases Al floc size, with higher SO 4 − concentration giving a greater reduction. • Low phosphate dosage promotes floc growth, while excessive dose inhibits coagulation. • Anions affect primary particle size/crystallinity by participating in hydrolysis. Coagulation efficiency is heavily contingent upon a profound comprehension of the underlying mechanisms, facilitated by the evolution of coagulation theory. However, the role of anions, prevalent components in raw and wastewaters, has been relatively overlooked in this context. To address this gap, this study has investigated the impact of three common anions (i.e., chloride, sulfate, and phosphate) on Al-based coagulation. The results have shown that the influence of anions on coagulation depends predominantly on their ability to compete with hydroxyl groups throughout the entire coagulation process, encompassing hydrolysis, aggregation, and the growth of large flocs. Moreover, this competition is subject to the dual influence of both anion concentration and hydroxyl concentration (i.e., pH). The results have revealed the intricate interplay between anions and coagulants, their impact on floc structure, and their importance in optimizing coagulation efficiency and ensuring the production of high-quality water. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel permanganate synthesis pathway in neutral pH, using ambient manganese (Mn2+). • Electro- and permanganate oxidation process employed for atrazine degradation. • Atrazine degradation increased significantly with permanganate production. • Degradation pathway proposed for both electro- and permanganate oxidation processes. A novel process involving the simultaneous electrochemical oxidation and electrosynthesis of permanganate oxidant has been explored for the treatment of the triazine organic herbicide, atrazine. The electrochemical synthesis of permanganate in neutral pH conditions using low concentration manganese (Mn2+), analogous to levels found in some raw groundwater sources, and their subsequent effect on atrazine degradation were studied in bench-scale experiments. Permanganate synthesis was found to be largely unaffected by the operating current density (10, 40 and 80 mA cm−2) during electrolysis, indicating as mass transport controlled process. Under the same operating conditions, hydroxyl radical mediated oxidation was observed to degrade atrazine from an initial concentration of 9.27 µM (2 mg L−1), to 6.22, 4.88 and 2.36 µM after 120 min of electrolysis for 10, 40 and 80 mA cm−2 conditions. When 55 µM (3.0 mg L−1) Mn2+ was added to the water matrix, atrazine degradation increased, yielding final concentrations of 5.80, 3.66 and 2.17 µM, respectively. Atrazine degradation was found to be accurately described by pseudo-first-order reaction kinetics, with and without the enhanced oxidation by permanganate generation, as the concentration of hydroxyl radicals remained constant and comparatively high throughout electrolysis. Finally, the yielded second-order reaction rate constants of electrochemically generated permanganate, and dosed potassium permanganate, with atrazine were 9.79 and 8.35 M−1 s−1, respectively, whereby the latter degradation mechanism was kinetically limited and the former was under mass transfer control due to an extremely low permanganate-atrazine ratio. Finally, four primary oxidation by-products were observed to form in the reactions, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine. [ABSTRACT FROM AUTHOR]

Summarizes the experience of treating low alkalinity, low turbidity, humic-rich surface waters by the combination of ozone oxidation and biological filtration processes. Treatment of upland colored waters in Great Britain, U.S. and other countries; Impact of oxidation on humic properties; Ozonation and activated carbon; Ozone and inorganic adsorbents.

This paper is concerned with the performance of relatively new kinds of pre-polymerised inorganic coagulants, poly-alumino-iron-sulphate (PAFS) and polyferric sulphate (PFS). Laboratory experiments were undertaken to evaluate the PAFS and PFS, in comparison with conventional coagulants such as ferric sulphate (FS) and aluminium sulphate (AS), for the coagulation of algal type model waters and a lowland surface water containing algae and natural organic matter (NOM). Experimental results demonstrated mat under the conditions studied, the performance of pre-polymerised coagulants were consistently superior to conventional coagulants (ie., FS and AS). This is attributed to the presence of a range of pre-formed polymerised species. The coagulation mechanism of PAFS and PFS has been discussed in the paper. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the relative importance of algae and algal derived organic precursors in the generation of Trihalomethane compounds (THMs). Laboratory tests have been earned out using cultures of two common algal species dominating natural reservoir populations to assess the importance of species, growth phase and biomass versus Extracellular product (ECP) in THM production. The results of the study showed that THMFP of algae cells and ECP increased with culture age formation from cells was more than double that from ECPS for Asterionella formosa and Anabaena flosaquae. It is predicted that typical blooms in a reservoir of either species could produce a substantial fraction of the THM's formed during chlorination. [ABSTRACT FROM AUTHOR]

• PAFC is a better alternative coagulant of FeSO 4 in Stevia pretreatment. • PAFC has higher impurity removal and no residual Fe(Ⅱ)-complex. • Solution pH had little effect on the performance of PAFC, but great effect on FeSO 4. • The addition of CaO increased membrane flux of the two coagulants. • The interaction between organic matter and nanoparticles blocked the gap of cake layer. Stevioside, mainly extracted from Stevia rebaudiana, is an important non-caloric additive for food, beverages and flavoring, and an alternative natural sweetener for people with diabetes and obesity. Pretreatment of Stevia rebaudiana, involving coagulation and filtration, is used to remove impurities from the leach liquor of stevia. Commercially, ferrous sulfate (FeSO 4) is commonly used as a coagulant in the factory, but large amounts of soluble Fe(Ⅱ)-protein complexes remain in the filtrate, which is potentially of health concern. In this study, the removal of impurities (particles and organic compounds) in leach liquor of stevia by polymeric aluminium ferric chloride (PAFC) was compared to FeSO 4 , through simulated coagulation and membrane filtration processes. The results showed that PAFC has a superior coagulation efficiency to FeSO 4 , achieving a very high removal of the impurities in the leaching solution without complexation, and which was not affected by the solution pH. In the subsequent membrane filtration, the flux was found to be influenced (reduced) by the interaction between organic matter (e.g. proteins) and nanoparticles in the cake layer, which formed a dense and compact structure with a lower permeability. Although using FeSO 4 had a greater membrane flux, the results have shown significant advantages in using PAFC as an alternative coagulant to FeSO 4 in the pre-treatment of leach liquor from Stevia processing. The higher treatment performance and acceptable membrane flux could be obtained by adjusting the pH of the leaching solution to 7 (addition of CaO), at the optimal PAFC dose (5000 mg/L). [ABSTRACT FROM AUTHOR]

• The planar flocs consisted of crystallineγ-FeOOH were formed in Fe(II) coagulation. • Fe(II) was present within the internal structure of γ-FeOOH. • The growth of γ-FeOOH was inhibited by the presence of HA. • The growth of γ-FeOOH was independent of DO concentration and pH. Although Fe(II) salts have been widely used as coagulants in water treatment for many years, the underlying mechanisms of their performance remain unclear. Here, we present a detailed study of the coagulation behavior of Fe(II) salts and crystallization of flocs, and investigate the effect of humic acid (HA) under different DO concentrations and pH conditions. The behavior of Fe(II) and Fe(III) coagulants was found to be markedly different with the flocs from Fe(II) consisting of planar-like crystalline γ-FeOOH in contrast to the small amorphous spherical-like flocs from Fe(III) dosing. The effect of HA on Fe(II) coagulation was different under different DO concentrations and pH, where by the growth of γ-FeOOH was inhibited by the presence of HA, but independent of DO concentration and pH. It was found that Fe(II) was present within the internal structure of γ-FeOOH, and a plausible formation mechanism is proposed. Firstly, planar nanoparticles of Fe(OH) 2 were formed via Fe(II) ion hydrolysis which then servedas the nucleus for subsequent crystal growth. With oxidation, Fe(II) on the surface of nanoparticles transformed to Fe(III). Finally, the formation of γ-FeOOH in Fe(II) coagulation was accompanied by a change in solution colour to yellow. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The practical applications of membrane-based water treatment techniques are constrained by the problem of membrane fouling. Various studies have revealed that interactions between extracellular polymeric substances (EPS) and the membrane surface determine the extent of irreversible fouling. Herein, we describe a novel bioelectrochemical system (BES) integrated with an ultrafiltration (UF) membrane in order to provide an enhanced antifouling property. It was found that the integrated BES membrane system had a superior performance compared to a conventional (control) UF system, as manifested by a much lower development of transmembrane pressure. The BES significantly reduced microbial viability in the membrane tank and the imposed electrode potential contributed to the degradation of biopolymers, which favored the alleviation of membrane fouling. Notably, the electron transfer between the acclimated microorganisms and the conductive membrane in the BES integrated system exhibited an increasing trend with the operation time, indicating a gradual increase in microbial electrical activity. Correspondingly, the accumulation of extracellular polymeric substances (EPS) on the membrane surface of the BES integrated system showed a substantial decrease compared to the control system, which could be attributed to a series of synergistic effects induced by the BES integration. The differences in the microbial diversity between the control and the BES integrated system revealed the microbial selectivity of the poised potential. Specifically, microbial strains with relatively high EPS production, like the genus of Zoogloea and Methyloversatilis , were reduced significantly in the BES integrated system, while the expression of the electroactive bacteria was promoted, which facilitated extracellular electron transfer (EET) and therefore the bioelectrochemical reactions. Overall, this study has presented a feasible and promising new approach for membrane fouling mitigation during the process of water treatment. Image 1 • A BES integrated UF system was developed to alleviate membrane fouling. • e - transfer and microbial electrical activity can be enhanced by BES integration. • BES integration contributes to low EPS accumulation on membrane surface. • BES integration promotes the expression of specific electroactive bacteria. [ABSTRACT FROM AUTHOR]

MXene is a metal-carbon/nitrogen compound material with a two-dimensional layered structure. As a new form of two-dimensional material, it has great potential in the field of water purification because of its properties of high permeability and hydrophilicity. In this study, a MXene composite membrane was prepared by in-situ oxidation of titanium dioxide on the MXene surface by an alkaline oxidation method. A series of characterizations of the prepared MXene composite membrane was carried out. Scanning electron microscopy showed that with an increasing degree of oxidation, the extent of agglomeration of MXene nanosheets increased, thus generating more water channels that are conducive to the transport of water molecules, and an increasing water flux. The penetration performance, interception performance, and stability of the MXene composite membrane were tested. The effect of different concentrations of KOH on the properties of the composite membrane was investigated. It was found that the flux of the composite membrane increased with alkali concentration by 4.6–28.8 times the flux without exposure to alkali. It was found that the rejection rate of the composite membrane for pollutants (dyes, humic acid, bovine serum albumin protein) decreased only slightly with increasing alkali concentration, and was ≥94% of the pure MXene membrane rejection rate in all cases. The rejection performance of the composite membrane was related to the size and charge properties of the pollutant molecules. The results of the stability tests showed that the composite membranes had a high degree of physical and flux stability in a range of aqueous solutions. [Display omitted] • Innovative MXene composite membrane was prepared by one-step alkaline oxidation. • Unique asymmetric structure was constructed utilizing agglomeration of MXene. • Ultra high flux and removal efficiency was achieved with long-term stability. [ABSTRACT FROM AUTHOR]

• Impacts of bioelectrochemical integration on biofiltration treating reclaimed water is explored. • Short-term bioelectrochemical integration enhances the removal of NOM and biopolymers. • Long-term bioelectrochemical integration favors autotrophic SO 4 2− reduction. • Microbial diversity and gene function are greatly influenced by bioelectrochemical integration. • Microbial-derived humic substances facilitate the electron transfer in syntrophic interactions. Biofiltration is an environmentally 'green' technology that is compatible with the recently proposed sustainable development goals, and which has an increasingly important future in the field of water treatment. Here, we explored the impacts of bioelectrochemical integration on a bench-scale slow rate biofiltration system regarding its performance in reclaimed water treatment. Results showed that the short-term (<3 months) integration improved the removal of natural organic matter (NOM) (approximately 8.8%). After long-term (5 months and thereafter) integration, the cathodic charge transfer resistance was found to have a significant reduction from 2662 to 1350 Ω. Meanwhile, bioelectrochemical autotrophic sulfate (SO 4 2−) reduction (over 27.6% reduction) through the syntrophic metabolism between hydrogen oxidation strains (genus Hydrogenophaga) and sulfate-reducing microbes (genera Dethiobacter, Desulfovibrio , and Desulfomicrobium) at the cathodic region was observed. More significantly, the microbial-derived chromophoric humic substances were found to act as electron shuttles at the cathodic region, which might facilitate the process of bioelectrochemical SO 4 2− reduction. Overall, this study provided valuable insights into the potential application of bioelectrochemical-integrated biofilter for simultaneous reduction of NOM and SO 4 2− treating reclaimed water. [Display omitted] [ABSTRACT FROM AUTHOR]