Pre-treatments to reduce fouling of low pressure micro-filtration (MF) membranes

Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles

The dissolution of silica and transparent exopolymer particles (TEP) can deposit on the membrane surface and cause serious membrane fouling in reverse osmosis (RO) technology. Coagulation, as a common pretreatment process for RO, can effectively intercept pollutants and alleviate membrane fouling. In this study, FeCl3 and AlCl3 coagulants and polyacrylamide (PAM) flocculants were used to explore the optimal coagulation conditions to reduce the concentration of silica and TEP in the RO process. The results showed that the two coagulants had the best removal effect on pollutants when the pH was 7 and the dosage was 50 mg/L. Considering the proportion of reversible fouling after coagulation, the removal rate of pollutants, and the residual amount of coagulation metal ions, the best PAM dosage was 5 mg/L for FeCl3 and 1 mg/L for AlCl3. After coagulation pretreatment, the Zeta potential decreased, and the particle size distribution increased, making pollutants tend to aggregate, thus effectively removing foulants. The removal mechanisms of pollutants by coagulation pretreatment were determined to be adsorption, electric neutralization and co-precipitation. This study determined the best removal conditions of silica and TEP by coagulation and explored the removal mechanism.

Integrating biological ion exchange with biological activated carbon treatment for drinking water: A novel approach for NOM removal, trihalomethane formation potential, and biological stability

Ion exchange resins (IEX) are used in drinking water utilities to remove natural organic matter (NOM) from surface water; however, the disposal of used brine can be a major drawback. Recently, biological ion exchange (BIEX) has been proposed as an alternative to biological activated carbon (BAC) for removing natural organic matter (NOM). The present study is, to the best of our knowledge, the first attempt to use a hybrid BIEX and BAC (BIEX+BAC) system for drinking water treatment. The removal of NOM, assimilable organic carbon, and trihalomethane formation potential was investigated by operating four columns comprising IEX, BIEX, BAC, and BIEX+BAC with 18,000 bed volumes. The BIEX+BAC system was the most effective at removing dissolved organic carbon (59.9%). Based on fluorescence excitation-emission matrix spectroscopy, the BIEX+BAC column showed the maximum removal rates in all peak regions of T1, T2, and A. Using liquid chromatography-organic carbon detection, resin-containing columns were found to effectively remove humic substances, which are the principal precursors of trihalomethanes. The lowest potential for trihalomethane formation was observed in BIEX+BAC. BIEX+BAC also had the highest assimilable organic carbon removal efficiency (61.2%) followed by BIEX (52.3%), BAC (49.5%), and IEX (47.1%). The BIEX+BAC hybrid was found to be the most effective method for removing NOM fractions and reducing the formation of disinfection byproducts.

Existing Filtration Treatment on Drinking Water Process and Concerns Issues

Water is one of the main sources of life's survival. It is mandatory to have good-quality water, especially for drinking. Many types of available filtration treatment can produce high-quality drinking water. As a result, it is intriguing to determine which treatment is the best. This paper provides a review of available filtration technology specifically for drinking water treatment, including both conventional and advanced treatments, while focusing on membrane filtration treatment. This review covers the concerns that usually exist in membrane filtration treatment, namely membrane fouling. Here, the parameters that influence fouling are identified. This paper also discusses the different ways to handle fouling, either based on prevention, prediction, or control automation. According to the findings, the most common treatment for fouling was prevention. However, this treatment required the use of chemical agents, which will eventually affect human health. The prediction process was usually used to circumvent the process of fouling development. Based on our reviews up to now, there are a limited number of researchers who study membrane fouling control based on automation. Frequently, the treatment method and control strategy are determined individually.

Reduced Low-Pressure Membrane Fouling by Inline Coagulation Pretreatment for a Colored River Water

Drinking water treatment (DWT) using low-pressure membranes (LPM) has become increasingly popular due to their many reported advantages compared to conventional technologies. Productivity decline due to fouling has prevented LPMs from becoming the technology of choice in DWT, however, coagulation pretreatment either with or without particle separation mitigates fouling phenomena. The effectiveness of coagulation/flocculation/sedimentation (CF-S), coagulation/flocculation/dissolved air flotation (CF-DAF), and inline coagulation (CF-IN) as technologies for pretreatment of feed water has rarely been investigated using the same water source. In this study, CF-S, CF-DAF, and CF-IN are directly compared as pretreatment of a tubular multi-channeled ultrafiltration (UF) membrane using the same highly colored river water. Three-day long filtration tests were performed using an automated bench-scale filtration apparatus with an inside-out configuration. Although CF-DAF had the greatest removal of dissolved organic matter (DOM) and hydrophobic organics, CF-S pretreatment resulted in a similar level of total fouling. Compared to CF-DAF and CF-S, CF-IN pretreatment resulted in lower fouling. The hydraulic and chemical reversibility of CF-IN fouling was seen to be strongly influenced by the feed water zeta potential, suggesting the importance of floc electrostatic and morphological characteristics on inline coagulation performance.

Review of adsorption-membrane hybrid systems for water and wastewater treatment

Adsorption is an effective method for the removal of inorganic and organic contaminants and has been commonly used as a pretreatment method to improve contaminant removal and control flux during membrane filtration. Over the last two decades, many researchers have reported the use of hybrid systems comprising various adsorbents and different types of membranes, such as nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) membranes, to remove contaminants from water. However, a comprehensive evaluation of the removal mechanisms and effects of the operating conditions on the transport of contaminants through hybrid systems comprising various adsorbents and NF, UF, or MF membranes has not been performed to date. Therefore, a systematic review of contaminant removal using adsorption-membrane hybrid systems is critical, because the transport of inorganic and organic contaminants via the hybrid systems is considerably affected by the contaminant properties, water quality parameters, and adsorbent/membrane physicochemical properties. Herein, we provide a comprehensive summary of the most recent studies on adsorption-NF/UF/MF membrane systems using various adsorbents and membranes for contaminant removal from water and wastewater and highlight the future research directions to address the current knowledge gap.

Efficacy of selected pretreatment processes in the mitigation of low-pressure membrane fouling and its correlation to their removal of microbial DOM

Membrane fouling by dissolved organic matter (DOM), especially microbially-derived DOM, is a major challenge for ultrafiltration (UF) membranes in water purification. Fouling may be mitigated by pretreating feed waters; however, there are no comprehensive studies that compare the fouling reduction efficacies across different pretreatment processes. Further, there is a limited understanding of the relationship between fouling reduction efficacy and microbially-derived DOM removal from source waters. Accordingly, the objectives of this study were to: (i) evaluate and compare the efficacies of five pretreatment processes in reducing UF membrane fouling by DOM; and (ii) investigate whether a relationship exists between membrane fouling reduction and microbially-derived DOM removal by pretreatment processes. We investigated seven water sources and a polyvinylidene fluoride hollow-fiber UF membrane using bench-scale fouling tests. Dissolved organic carbon content, ultraviolet absorbance and fluorescence excitation-emission matrix spectroscopy were used to assess DOM concentration and composition. Alum and ferric chloride coagulation were the most effective pretreatment processes in reducing membrane fouling, anion exchange was moderately effective, and PAC adsorption and chlorine pre-oxidation were the least effective. Consistent with previous studies, microbially-derived DOM was the major contributor to UF membrane fouling regardless of water source or pretreatment type. Fouling reduction was strongly correlated with the reduction of microbially-derived DOM in foulant layers but not from source waters. This result indicates that a fraction of the total microbially-derived DOM in feed waters was responsible for UF fouling. Overall, pretreatment processes that remove microbially-derived DOM are well-suited for UF membrane fouling reduction.

Impacts of composite flocculant in coagulation/ultrafiltration hybrid process for treatment of humic acid water: the role of basicity

The effects of the composite flocculant, polyaluminium chloride and poly dimethyldiallylammonium chloride (PACl-PDMDAAC) in comparison with PACl on coagulation efficiencies and membrane fouling in coagulation-ultrafiltration (C-UF) process were analysed, which was conducted in the conditions of different basicity (B) values and the presence of Mg²⁺. Results showed that PACl-PDMDAAC enhanced the ability of charge neutralization and absorption bridging, and improved the coagulation efficiency. When B value was 1.5, the flocculant hydrolyzed to form more Al_b morphology and effectively removed HA molecules. The presence of Mg²⁺ could improve the coagulation performance through bridging ability. The results of the ultrafiltration test showed that the flux reduction for PACl was 70%, while the flux reduction for PACl-PDMDAAC was 60% in C-UF process. PACl-PDMDAAC could effectively reduce membrane fouling mainly by reducing strongly attached cake/gel layer. When B value was 1.5, the Al_b content of the flocculant was higher and the ability of adsorption charge neutralization was strong, resulting in forming a stable cake layer. Therefore, the membrane fouling was the lightest. In addition, the presence of Mg²⁺ in raw water reduced the membrane fouling.

Synergistic fouling behaviors and mechanisms of calcium ions and polyaluminum chloride associated with alginate solution in coagulation-ultrafiltration (UF) process

Effects of calcium ions and polyaluminum chloride (PACl) on membrane fouling in coagulation-ultrafiltration (UF) process were investigated in this study. Filtration tests demonstrated three interesting filtration behaviors: 1) high specific filtration resistance (SFR) of alginate solution with low CaCl₂ or PACl addition (e. g. 3.51×10¹⁵ m·kg ^-1 under the condition of 1.5 mM CaCl₂ addition); 2) unimodal pattern of alginate SFR with PACl or CaCl₂ addition alone; 3) synergistic effects between CaCl₂ and PACl on alginate SFR. It was found that, the foulant morphological changes driven by the thermodynamic mechanisms based on Flory-Huggins lattice theory take the critical roles in these filtration behaviors. Density functional theory (DFT) calculations showed that initial coordination of Ca²⁺ and Al³⁺ ions with alginates tended to form tetrahedron geometry and geometry of coordinating three terminal carboxyl groups, respectively, which facilitated to elongate the alginate chains (without clustering the flocs) and form more stable gel, increasing SFR. Improving Ca²⁺ and Al³⁺ dosages triggered transition to other geometries for clustering polymeric network and flocculation, reducing SFR. Due to the higher binding affinity of Ca²⁺ over Al³⁺, Ca²⁺ and Al³⁺ sequentially take roles of enlarging polymeric network and clustering the coordination compounds, and then facilitate to form large size flocs and reduce SFR, causing the synergistic effects between CaCl₂ and PACl additions. The proposed thermodynamic mechanisms satisfactorily explained these interesting fouling behaviors, allowing to further optimize coagulation-UF process.

Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-Of-The-Art and Performance Analysis

Wastewater reuse as a sustainable, reliable and energy recovery concept is a promising approach to alleviate worldwide water scarcity. However, the water reuse market needs to be developed with long-term efforts because only less than 4% of the total wastewater worldwide has been treated for water reuse at present. In addition, the reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility based on their local water reuse guidelines. Moreover, municipal wastewater as an alternative water resource for non-potable or potable reuse, has been widely treated by various membrane-based treatment processes for reuse applications. By collecting lab-scale and pilot-scale reuse cases as much as possible, this review aims to provide a comprehensive summary of the membrane-based treatment processes, mainly focused on the hydraulic filtration performance, contaminants removal capacity, reuse purpose, fouling resistance potential, resource recovery and energy consumption. The advances and limitations of different membrane-based processes alone or coupled with other possible processes such as disinfection processes and advanced oxidation processes, are also highlighted. Challenges still facing membrane-based technologies for water reuse applications, including institutional barriers, financial allocation and public perception, are stated as areas in need of further research and development.

Precoating membranes with submicron super-fine powdered activated carbon after coagulation prevents transmembrane pressure rise: Straining and high adsorption capacity effects

Commercially available powdered activated carbon (PAC) with a median diameter of 12-42 μm was ground into 1 μm sized superfine PAC (SPAC) and 200 nm sized submicron SPAC (SSPAC) and investigated as a pretreatment material for the prevention of hydraulically irreversible membrane fouling during a submerged microfiltration (MF) process. Compared with PAC and SPAC, SSPAC has a high capacity for selective biopolymer adsorption, which is a characteristic found in natural organic matter and is commonly considered to be a major contributor to membrane fouling. Precoating the membrane surface with SSPAC during batch filtration further removes the biopolymers by straining them out. In lab-scale membrane filtration experiments, an increase in the transmembrane pressure (TMP) was almost completely prevented through a precoating with SSPAC based on its pulse dose after coagulation pretreatment. The precoated SSPAC formed a dense layer on the membrane preventing biopolymers from attaching to the membrane. Coagulation pretreatment enabled the precoated activated carbon to be rinsed off during hydraulic backwashing. The functionality of the membrane was thereby retained for a long-term operation. Precoating the membranes with SSPAC after coagulation is a promising way to control membrane fouling, and efficiently prevents an increase in the TMP because of the straining effect of the SSPAC and the high capacity of the SSPAC to adsorb any existing biopolymers.

Using EEM-PARAFAC to probe NF membrane fouling potential of stabilized landfill leachate pretreated by various options

Pretreatment processes substantially modify the organic composition of landfill leachate, which affect the fouling behavior in the post-treatment of membrane filtration. In this study, the changes in the chemical composition of stabilized landfill leachate upon various pretreatments, which encompassed coagulation/flocculation (C/F), ion exchange resins (MIEX), granular activated carbon (GAC) adsorption, and their combinations, were tracked via excitation emission matrix - parallel factor analysis (EEM-PARAFAC), and the membrane fouling potentials were assessed in the subsequent processes of nanofiltration (NF). Fluorescence components, fulvic-like (C1), protein-like (C2), and humic-like (C3), were identified and validated using EEM-PARAFAC. MIEX and C/F pretreatments were not effective to remove C1 and C2, which were associated with relatively small sized and hydrophilic molecules. GAC adsorption did not show any preference with the removal towards different components. These differences in the chemical heterogeneity among the variously pretreated leachates led to the discrepancies in membrane fluxes at a similar leachate concentration. The result also signified the importance of probing the chemical composition of pretreated leachate for the optimization of the post membrane filtration. The sum of C2 and C3 in the pretreated leachate showed a good correlation with reversible membrane fouling resistance (r = 0.93; p < 0.05), while C1 was highly correlated with irreversible membrane resistance (r = 0.872; P < 0.05). These findings provided a new insight into the applicability of fluorescence spectroscopy for tracking the changes in the membrane fouling potential of stabilized landfill leachate after various pretreatments.

Novel H2O2-MnO2 system for efficient physico-chemical cleaning of fouled ultrafiltration membranes by simultaneous generation of reactive free radicals and oxygen

The novel H₂O₂-MnO₂ system was developed to achieve highly efficient membrane cleaning for both fouled PVDF and PES membranes in this study. Compared with conventional chemical cleaning process in which the whole membrane module had to be soaked in highly concentrated solution of chemical reagent for long period of time, the H₂O₂-MnO₂ cleaning process conducting for only 5 min in 0.5 wt% H₂O₂ solution could achieve more than 95% recovery of permeate flux and almost total removal of the irreversible foulants. More importantly, the permeate flux and filtration efficiency of the membrane could be still kept stable after 6 runs of consecutive fouling and cleaning. Based on the systematic microscopic analyses, Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FTIR), as well as the quenching experiments with different free radical scavengers, the outstanding performance of H₂O₂-MnO₂ system was attributed to the generation of both free radicals and abundant oxygen simultaneously, leading to the physico-chemical membrane cleaning. Conclusively, the newly developed H₂O₂-MnO₂ system demonstrated noteworthy advantages on efficient membrane cleaning, and exhibited highly potential for the wide application in practical water treatment process.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Effect of turbidity on micropollutant removal and membrane fouling by MIEX/ultrafiltration hybrid process

Effect of turbidity on the removal of organic micropollutant (carbamazepine, CBZ) through magnetic ion exchange (MIEX) resin combined with ultrafiltration (UF) was investigated in this study. The purification behaviors of the MIEX/UF processes were studied through scanning electron microscopy, high-performance liquid chromatography, zeta potential and particle size distribution analyses. The experimental results show that 64-74% of CBZ in different turbidities could be removed by MIEX resin under the optimum dose and contact time, while water sample with turbidity of 20 ± 1.1 NTU present minimum CBZ removal rate of 64% and turbidity of 60 ± 1.0 NTU led to maximum removal efficiency of 74%. The results of UF experiments showed that UF could not efficiently remove CBZ. Alternatively, UF was more suitable for removing turbidity than MIEX resin. In a separate UF system, the turbidity (20 ± 1.1 NTU) led to a flux reduction of 60% at the first filtration cycle, while the reduction for 1.0 ± 0.1 NTU, 40 ± 1.0 NTU and 60 ± 1.0 NTU were 48%, 52% and 45%, respectively. For the water samples with different turbidities, obvious decrease in membrane fouling was observed after MIEX pretreatment, meanwhile the CBZ/turbidity removal could be improved. The UF membrane was used four times after backwashing to research the reusability of membrane. The integrated processes combining MIEX resin with UF could significantly improve membrane recycling effect and prevent secondary pollution caused by resin.

A comparison study of in-situ coagulation and magnetic ion exchange (MIEX) as pre-treatments for ultrafiltration: Evaluating effectiveness of organic matters removals and fouling mitigation

This work was designed to compare the effectiveness of in-situ coagulation and MIEX as pre-treatments prior to ultrafiltration (UF) to improve organic matter (OM) removal and mitigate membrane fouling. Three kinds of OMs, i.e. salicylic acid (SA), humic acid (HA) and bovine serum albumin (BSA) were employed. The experimental results show that coagulation-UF led to most effective removal of HA (almost 90%), while the SA was uncoagulated and least removable, with the rejection rate of about 55%. Conversely, MIEX present superior ability for removing SA, contributing to additional efficiency of 71.95-77.21% than UF alone. Proper dosage of Al-based coagulants could alleviate flux loss, especially in the cases of HA and BSA. Increasing coagulant dose resulted in continuous decrement of irreversible resistance (R_ir), which dominated the membrane fouling development by the SA water. For HA and BSA waters, alternatively, variations of R_r determined the flux declines. Floc compact degree was the decisive factor for R_r for coagulated SA; while for HA and BSA, R_r was most related to the floc size and foulant-foulant interaction. MIEX was most effective for alleviating flux loss when treating the hydrophilic SA with small molecules and for all the cases, MIEX exerted little influence on the R_r values.

Operating Cost Reduction of In-line Coagulation/Ultrafiltration Membrane Process Attributed to Coagulation Condition Optimization for Irreversible Fouling Control

This study examined the optimum coagulation conditions for reducing irreversible fouling during the in-line coagulation/ultrafiltration (UF) membrane process and assessed the decrease in operating cost. The coagulation conditions that generated charge-neutralization, sweep-flocculation, and under-dosing mechanisms were obtained by a jar-test, and a pilot-scale in-line coagulation/UF membrane process was operated under the coagulation conditions. Charge-neutralization and sweep-flocculation mechanisms reduced irreversible fouling effectively, and the under-dosing mechanism was able to reduce irreversible fouling only when flocs of a certain size or larger were formed. This revealed that floc size was a more important factor in reducing irreversible fouling than floc structure, and once initial cake layers were created by flocs of a fixed size, the structure of formed cake layers had only a minor effect on irreversible fouling. Regarding reduction in operating cost, 0.5 mg/L and 3 h, which were necessary to produce an under-dosing mechanism, were deemed the optimum coagulant dosage and coagulant injection time, respectively, to reduce irreversible fouling. In order to analyze the operating cost reduction effect, a pilot plant was operated under optimum operating conditions, and the total operating cost was approximately 11.2% lower than without in-line coagulation.

The impact of loading approach and biological activity on NOM removal by ion exchange resins

The present study investigated the impact of different loading approaches and microbial activity on the Natural Organic Matter (NOM) removal efficiency and capacity of ion exchange resins. Gaining further knowledge on the impact of loading approaches is of relevance because laboratory-scale multiple loading tests (MLTs) have been introduced as a simpler and faster alternative to column tests for predicting the performance of IEX, but only anecdotal evidence exists to support their ability to forecast contaminant removal and runtime until breakthrough of IEX systems. The overall trends observed for the removal and the time to breakthrough of organic material estimated using MLTs differed from those estimated using column tests. The results nonetheless suggest that MLTs could best be used as an effective tool to screen different ion exchange resins in terms of their ability to remove various contaminants of interest from different raw waters. The microbial activity was also observed to impact the removal and time to breakthrough. In the absence of regeneration, a microbial community rapidly established itself in ion exchange columns and contributed to the removal of organic material. Biological ion exchange (BIEX) removed more organic material and enabled operation beyond the point when the resin capacity would have otherwise been exhausted using conventional (i.e. in the absence of a microbial community) ion exchange. Furthermore, significantly greater removal of organic matter could be achieved with BIEX than biological activated carbon (BAC) (i.e. 56 ± 7% vs. 15 ± 5%, respectively) when operated at similar loading rates. The results suggest that for some raw waters, BIEX could replace BAC as the technology of choice for the removal of organic material.

Removal of natural organic matter (NOM) from water by ion exchange - A review

Natural organic matter (NOM) is present in underground and surface waters. The main constituents of NOM are humic substances, with a major fraction of refractory anionic macromolecules of various molecular weights. The NOM concentration in drinking water is typically 2-10 ppm. Both aromatic and aliphatic components with carboxylic and phenolic functional groups can be found in NOM, leading to negatively charged humic substances at the pH of natural water. The presence of NOM in drinking water causes difficulties in conventional water treatment processes such as coagulation. Problems also arise when applying alternative treatment techniques for NOM removal. For example, the most significant challenge in nanofiltration (NF) is membrane fouling. The ion exchange process for NOM removal is an efficient technology that is recommended for the beginning of the treatment process. This approach allows for a significant decrease in the concentration of NOM and prevents the formation of disinfection byproducts (DBPs) such as trihalomethanes (THMs). This article provides a state-of-the-art review of NOM removal from water by ion exchange.

Operating cost reduction of UF membrane filtration process for drinking water treatment attributed to chemical cleaning optimization

This study investigated the cost and CO₂ emission reduced as a result of optimizing operating conditions for chemical cleaning in a membrane filtration process used for water treatment. A new protocol was proposed and operating conditions for chemical cleaning of a pilot-scale membrane filtration process were optimized. The critical flux for irreversibility was identified as the permeate flux using a modified flux-step method, and was 100 l m^-2 h^-1, 20 l m^-2 h^-1 higher than the vendor recommended permeate flux. NaOCl, which is also the vendor recommended chemical, was selected as the optimal chemical reagent following an examination of the permeability restoration ratios and nature of the irreversible foulants. The optimized operating conditions of enhanced flux maintenance (EFM), determined using response surface methodology (RSM) were: 6.3 d interval, 500 ppm concentration, and 76 min duration, which represented an increase of 4.3 d, 300 ppm, and 36 min, respectively, as opposed to the vendor recommended conditions. As a result, the total operating cost and CO₂ emission were $0.1187/m³ and 112.75 g CO₂/m³, respectively, and 26.5% lesser compared to the operating cost and CO₂ emission based on vendor recommended conditions. This study found that the reductions in operating cost and CO₂ emission using the optimization process were excellent.

Efficient control of membrane fouling in MF by removal of biopolymers: Comparison of various pretreatments

In recent studies on membrane fouling in microfiltration (MF) and ultrafiltration (UF) for drinking water production, hydrophilic macromolecular organics referred to as biopolymers have been shown to be major players in the fouling. In this study, various pretreatments were compared to maximize removal of biopolymers and to control membrane fouling efficiently. Multiple water samples were collected from different drinking water sources and were used in this study. Coagulation using polyaluminum chloride (PACl) was carried out under conditions of different dosages and different pHs and was also carried out in combination with the use of powdered activated carbon (PAC) or magnetic ion exchange (MIEX^®) resin. The efficiency of removal of biopolymers was highest by the combination of MIEX^® and coagulation regardless of the type of sample. Efficient removal of biopolymers achieved by the combination of MIEX^® and coagulation led to efficient control of membrane fouling in MF, which was confirmed by bench-scale filtration tests conducted under a constant flux of 62.5 LMH using commercially available hollow-fiber membranes. Enhanced coagulation with increased coagulant dosage or acidic coagulation (pH = 6) also exhibited good removal of biopolymers in some cases and led to control of fouling. In contrast, the combination of PAC and coagulation sometimes caused more rapid evolution of fouling by forming cake layers on the membrane surface. Results of bench-scale tests showed that the concentration of biopolymers in the feed water correlated well with the degree of physically irreversible fouling, which was dominant in this study. The strong correlation was shown with multiple water samples treated by various pretreatments, demonstrating that biopolymer concentration in feed water is a good index for fouling studies.

Integrated bicarbonate-form ion exchange treatment and regeneration for DOC removal: Model development and pilot plant study

The application of bicarbonate-form anion exchange resin and sodium bicarbonate salt for resin regeneration was investigated in this research is to reduce chloride ion release during treatment and the disposal burden of sodium chloride regeneration solution when using traditional chloride-form ion exchange (IX). The target contaminant in this research was dissolved organic carbon (DOC). The performance evaluation was conducted in a completely mixed flow reactor (CMFR) IX configuration. A process model that integrated treatment and regeneration was investigated based on the characteristics of configuration. The kinetic and equilibrium experiments were performed to obtain required parameters for the process model. The pilot plant tests were conducted to validate the model as well as provide practical understanding on operation. The DOC concentration predicted by the process model responded to the change of salt concentration in the solution, and showed a good agreement with pilot plant data with less than 10% difference in terms of percentage removal. Both model predictions and pilot plant tests showed over 60% DOC removal by bicarbonate-form resin for treatment and sodium bicarbonate for regeneration, which was comparable to chloride-form resin for treatment and sodium chloride for regeneration. Lastly, the DOC removal was improved by using higher salt concentration for regeneration.

Minimization of short-term low-pressure membrane fouling using a magnetic ion exchange (MIEX(®)) resin

Two challenges to low-pressure membrane (LPM) filtration are limited rejection of dissolved organic matter (DOM) and membrane fouling by DOM. The magnetic ion exchange resin MIEX(®) (Ixom Watercare Inc.) has been demonstrated to remove substantial amounts of DOM from many source waters, suggesting that MIEX can both reduce DOM content in membrane feed waters and minimize LPM fouling. We tested the effect of MIEX pretreatment on the reduction of short-term LPM fouling potential using feed waters varying in DOM concentration and composition. Four natural and two synthetic waters were studied and a polyvinylidene fluoride (PVDF) hollow-fiber ultrafiltration membrane was used in membrane fouling tests. To evaluate whether MIEX removes the fractions of DOM that cause LPM fouling, the DOM in raw, MIEX-treated, and membrane feed and backwash waters was characterized in terms of DOM concentration and composition. Results showed that: (i) the efficacy of MIEX to reduce LPM fouling varies broadly with source water; (ii) MIEX preferentially removes terrestrial DOM over microbial DOM; (iii) microbial DOM is a more important contributor to LPM fouling than terrestrial DOM, relative to their respective concentrations in source waters; and (iv) the fluorescence intensity of microbial DOM in source waters can be used as a quantitative indicator of the ability of MIEX to reduce their membrane fouling potential. Thus, when ion exchange resin processes are used for DOM removal towards membrane fouling reduction, it is advisable to use a resin that has been designed to effectively remove microbial DOM.

Aluminum-induced changes in properties and fouling propensity of DOM solutions revealed by UV-vis absorbance spectral parameters

The integration of pre-coagulation with ultrafiltration (UF) is expected to not only reduce membrane fouling but also improve natural organic matter (NOM) removal. However, it is difficult to determine the proper coagulant dosage for different water qualities. The objective of this study was to probe the potential of UV-vis spectroscopic analysis to reveal the coagulant-induced changes in the fouling potentials of dissolved organic matter (DOM) and to determine the optimal coagulant dosage. The Zeta potentials (ZPs) and average particle size of the four DOM solutions (Aldrich humic acid (AHA), AHA-sodium alginate (SA), AHA-bovine serum albumin (BSA) and AHA-dextran (DEX)) coagulated with aluminum chloride (AlCl3) were measured. Results showed that increasing the aluminum coagulant dosage induced the aggregation of DOM. Meanwhile, the addition of aluminum coagulant resulted in an increase in DSlope(325-375) (the slope of the log-transformed absorbance spectra from 325 to 375 nm) and a decrease in S(275-295) (the slope of the log-transformed absorption coefficient from 275 to 295 nm) and SR (the ratio of Slope(275-295) and Slope(350-400)). The variations of these spectral parameters (i.e., DSlope(325-375), S(275-295) and SR) correlated well with the aluminum-caused changes in ZPs and average particle size. This implies that spectral parameters have the potential to indicate DOM aggregation. In addition, good correlations of spectral parameters and membrane fouling behaviors (i.e., unified membrane fouling index (UMFI)) suggest that the changes in DSlope(325-375), S(275-295) and SR were indicative of the aluminum-caused alterations of fouling potentials of all DOM solutions. Interestingly, the optimal dosage of aluminum (40 μM for AHA, AHA-BSA, and AHA-DEX) was obtained based on the relation between spectral parameters and fouling behaviors. Overall, the spectroscopic analysis, particularly for the utilization of spectral parameters, provided a convenient approach for the exploration of combined coagulation and UF systems for DOM removal.

Molecular Mechanisms of Ultrafiltration Membrane Fouling in Polymer-Flooding Wastewater Treatment: Role of Ions in Polymeric Fouling

Polymer (i.e., anionic polyacrylamide (APAM)) fouling of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes and its relationships to intermolecular interactions were investigated using atomic force microscopy (AFM). Distinct relations were obtained between the AFM force spectroscopy measurements and calculated fouling resistance over the concentration polarization layer (CPL) and gel layer (GL). The measured maximum adhesion forces (Fad,max) were closely correlated with the CPL resistance (Rp), and the proposed molecular packing property (largely based on the shape of AFM force spectroscopy curve) of the APAM chains was related to the GL resistance (Rg). Calcium ions (Ca(2+)) and sodium ions (Na(+)) caused more severe fouling. In the presence of Ca(2+), the large Rp corresponded to high foulant-foulant Fad,max, resulting in high flux loss. In addition, the Rg with Ca(2+) was minor, but the flux recovery rate after chemical cleaning was the lowest, indicating that Ca(2+) created more challenges in GL cleaning. With Na(+), the fouling behavior was complicated and concentration-dependent. The GL structures with Na(+), which might correspond to the proposed molecular packing states among APAM chains, played essential roles in membrane fouling and GL cleaning.

Simultaneous removal of phosphorus and EfOM using MIEX, coagulation, and low-pressure membrane filtration

The feasibility of using magnetic ion exchange (MIEX) treatment, in-line alum coagulation, and low-pressure membrane filtration was investigated for the simultaneous removal of total phosphorus (TP) and effluent organic matter (EfOM) from biologically treated wastewater. The focus was also placed on minimizing fouling of polyvinylidene fluoride and polyethersulfone membranes, which are the most commonly used low-pressure membranes in new and retrofit wastewater treatment plants. MIEX alone was effective for the removal of EfOM, and MIEX plus a small alum dose was very effective in removing both EfOM and TP. MIEX removed phosphorus, but organic acids in EfOM were preferentially removed, and the effects of competing anions on the removal of EfOM were insignificant. All the pretreatment strategies decreased the resistance to filtration. The greatest decrease in fouling was achieved by using MIEX (15 mL L⁻¹) plus a very low dose of alum (∼0.5 mg Al L⁻¹). Sweep floc coagulation using alum and without MIEX also significantly decreased fouling but did not effectively remove EfOM and produced high floc volume that could be problematic for inside-out hollow-fibre modules. The addition of these reagents into rapid mix followed by membrane filtration would provide operational simplicity and could be easily retrofitted at existing membrane filtration facilities.

Combined BAC and MIEX pre-treatment of secondary wastewater effluent to reduce fouling of nanofiltration membranes

Biological activated carbon (BAC) and magnetic ion exchange resin (MIEX) were used to pre-treat secondary wastewater effluent (SWWE) and assessed for their capacity to reduce fouling of a nanofiltration membrane. BAC pre-treated water facilitated a lower but a steady flux while MIEX treated water resulted in a higher but a rapidly declining flux. Their combined use increased average flux from 58 to 89%. MIEX combined with BAC, in that order, was superior in reducing membrane fouling. Measurement of average Stokes radius (m) and apparent molecular weight distribution of dissolved organic matter (DOM), by nuclear magnetic resonance (NMR) and liquid chromatography organic carbon detection (LC-OCD), respectively, revealed that the microbial activity of BAC changed the nature of organic matter, probably by increasing the size of DOM molecules. BAC generally decreased the lower apparent molecular weight (LMW) fraction of dissolved organic carbon (DOC). Hence, the removal of LMW DOC and an increase of average Stokes radius (m) of DOM appeared to be important in facilitating a longer steady flux. Specifically, the combined MIEX/BAC pre-treatments appeared to target and reduce the foulants in SWWE that are largely responsible for the reduction of flux in nanofiltration membranes.

High-rate MIEX filtration for simultaneous removal of phosphorus and membrane foulants from secondary effluent

This work was designed to evaluate the effectiveness of magnetic ion exchange (MIEX) resin under the best possible conditions, passage through a fixed-bed of resin as opposed to the alternative of directly adding resin into a flowing stream. The possibility of using a very small amount of alum in addition to MIEX treatment was also investigated not only to adsorb residual EfOM in the effluent from a bed of MIEX but also to produce a porous cake layer that would keep away foulants from the surface of membrane or its pore walls. The MIEX treatment alone reduced fouling, but to a much lesser extent than for MIEX combined with an under-dosing coagulation (which uses a considerably low amount of alum). Almost all of colloids and organic acids were removed and the nearly complete removal of phosphorus was achieved by MIEX in a fixed-bed even for an extremely short hydraulic retention time of wastewater in the resin bed. MIEX resin removed phosphorus, but organic acids in EfOM were preferentially removed and the effects of competing anions on the removal of EfOM were insignificant. The MIEX treatment with added alum (only 0.5 mg Al L(-1)) dramatically improved the performance of MF and UF membranes and the subsequent membrane filtration also achieved ≤0.01 mg L(-1) of residual phosphorous. This condition also allowed good flux recovery after hydraulic flushing.

Reprint of "Characterization of cyclodextrin containing nanofilters for removal of pharmaceutical residues"

Due to the increasing amount of persistent organic pollutants (POPs) in general and pharmaceutical residues in particular in municipal wastewater, the efficiency of water treatment technologies should be improved. Following the biological treatment of wastewater nanofiltration offers a possible way for the removal of POPs. In this study β-cyclodextrin containing nanofilters having different chemical composition and thickness (1.5-3.5 mm) were investigated. For their characterization, their adsorption capacity was determined applying ibuprofen containing model solution and total organic carbon (TOC) analyzer. It could be established that the regeneration of nanofilters with ethanol and the application of inorganic additives (NaCl, NaHCO3, NH4HCO3) increased the adsorption capacity of nanofilters. The best results were achieved with chemical composition of 30 m/m% β-cyclodextrin polymer beads and 70 m/m% ultra-high molecular weight polyethylene in the presence of 1 2mmol ammonium hydrogen carbonate/nanofilter.

Characterization of cyclodextrin containing nanofilters for removal of pharmaceutical residues

Due to the increasing amount of persistent organic pollutants (POPs) in general and pharmaceutical residues in particular in municipal wastewater, the efficiency of water treatment technologies should be improved. Following the biological treatment of wastewater nanofiltration offers a possible way for the removal of POPs. In this study β-cyclodextrin containing nanofilters having different chemical composition and thickness (1.5-3.5mm) were investigated. For their characterization, their adsorption capacity was determined applying ibuprofen containing model solution and total organic carbon (TOC) analyzer. It could be established that the regeneration of nanofilters with ethanol and the application of inorganic additives (NaCl, NaHCO3, NH4HCO3) increased the adsorption capacity of nanofilters. The best results were achieved with chemical composition of 30m/m% β-cyclodextrin polymer beads and 70m/m% ultra-high molecular weight polyethylene in the presence of 12mmol ammonium hydrogen carbonate/nanofilter.

Experimental and computational investigations of the interactions between model organic compounds and subsequent membrane fouling

The formation of aggregates of sodium alginate and bovine serum albumin (BSA) (as representative biopolymers) with humic acid were detected by Liquid Chromatography (LC) UV254 response in the biopolymer region for mixture solutions. BSA interaction with humic acid showed that aggregation occurred both in the presence and absence of calcium, suggesting that multivalent ions did not play a part in the aggregation process. Similar analyses of the alginate interaction with humic acid also showed a positive interaction, but only in the presence of calcium ions. The fouling characteristics for the BSA-humic acid mixture appeared to be significantly greater than the fouling characteristics of the individual solutions, while for the sodium alginate-humic acid mixture, the fouling rate was similar to that of the sodium alginate alone. The effectiveness of hydraulic backwashing, 10-15% reversibility, was observed for the BSA-humic acid mixture, while the % reversibility was 20-40% for the sodium alginate-humic acid mixture. Increased humic acid and DOC rejection were observed for both BSA-humic acid and sodium alginate-humic acid solutions compared to the individual solutions, indicating that the biopolymer filter cakes were able to retain humic acids. When compared with BSA-humic acid mixture solution, greater removal of humic acid was observed for alginate-humic mixture, suggesting that sodium alginate may have a greater capacity for associations with humic acid when in the presence of calcium than BSA. Complementary molecular dynamics simulations were designed to provide insights into the specific mechanisms of interaction between BSA and humic acid, as well as between alginate and humic acid. For the BSA-humic acid system; electrostatic, hydrophobic and hydrogen bonding were the dominant types of interactions predicted, whilst divalent ion-mediated bonding was not identified in the simulations, which supported the LC-results. Similarly for the alginate-humic acid system, the interactions predicted were divalent ion-mediated interactions only and this was also supported the LC results. This work suggests that LC-UV254 might be used to identify aggregated biopolymers, and that combined with current characterisation techniques, be used to better explain performance variations between water sources.

Granular iron oxide adsorbents to control natural organic matter and membrane fouling in ultrafiltration water treatment

Fine iron oxide particles (IOPs) are effective in removing natural organic matter (NOM) that causes membrane fouling in water treatment, but the separation of used IOPs is problematic. This study focused on the fabrication and use of granular iron oxide adsorbents, in combination with ultrafiltration (UF) membranes while investigating the NOM removal efficiency and fouling control. Sulfonated styrene-divinylbenzene copolymer beads were coated with two types of iron oxides (ferrihydrite and magnetite) and their performances were compared to that of fine IOPs. A significant amount of iron oxide coating (52-63 mg of Fe per g bead) was achieved by means of electrostatic binding and hydrolysis of iron ions. Iron oxide coated polymer (IOCP) beads were able to remove some amounts (≈ 20%) of dissolved organic carbon (DOC) comparable to that achieved by IOPs within a short period of time (<15 min). Regenerated IOCPs exhibited the same sorption capacity as the fresh ones. The integrated IOCP/UF system operation with a 15-min empty bed contact time and 10-h cyclic regeneration maintained the 20% DOC removal with no sign of significant membrane fouling. In contrast, a sharp transmembrane pressure buildup occurred in the UF system when no iron oxide pretreatment was applied, regardless of the types of membranes tested. Iron oxide adsorbed the NOM fraction with molecular weights of >1000 kDa which is believed to be responsible for severe UF fouling.

Effect of different temperatures on performance and membrane fouling in high concentration PAC-MBR system treating micro-polluted surface water

A bench-scale immersed microfiltration coupled with 50 g/L PAC was developed to treat micro-polluted surface water (MPSW) under 10 and 20 °C and the effects of temperatures on the performance and the membrane fouling were also investigated. The low temperature (10 °C) delayed the time for the start-up by 9 days and the complete nitrification by 10 days. In the stable operation, two systems both had high NH₃-N removal efficiency (above 90%) and better removal of organic matters (10% DOC, 5% UV₂₅₄ and 4% SUVA) at 10 °C. Polysaccharides (SMP) were the main membrane fouling matters at low temperature (10 °C) and low temperature (10 °C) didn't cause serious chemical irreversible membrane fouling.