磁性离子交换树脂与超滤膜联用处理淮河原水

采用磁性离子交换树脂(MIEX)/混凝沉淀/超滤膜(UF)工艺处理淮河原水,考察了对有机物的去除特性以及MIEX预处理控制膜污染的效果.结果表明:UF出水浊度稳定在0.1NTU以下,粒径>2 μm的颗粒数平均为11个/mL,粒径>10μm的颗粒物被完全去除;组合工艺对CODMn和UV254的去除率分别为75.3%和90%,且能有效去除不同分子质量区间的有机物;系统对疏水性有机物(HOM)、弱疏水性有机物(WHOM)、荷电亲水有机物(HIC)的去除效果均较好,去除率分别为94.6%、82.7%和81.3%;组合工艺对三卤甲烷生成势(THMFP)和卤乙酸生成势(HAAFP)的去除率分别为90.7%和87.6%;MIEX预处理可有效减缓膜污染,运行期间超滤膜的跨膜压差上升缓慢,经水力反冲洗后跨膜压差就基本得到恢复.     

Autopsy of high-pressure membranes to compare effectiveness of MF and UF pretreatment in water reclamation

A pilot-plant study was designed to compare the effectiveness of microfiltration (MF) and ultrafiltration (UF) as pretreatment for high-pressure membranes in reclamation of biologically treated wastewater effluent. Granular media, filtered secondary effluent from a full-scale wastewater treatment plant, was fed to MF and UF units that operated in parallel. Each of these filtrates served as the feedwater to two reverse osmosis (RO) units and one nanofiltration (NF) unit that operated in parallel. The decline in specific flux was substantially lower for high-pressure membranes receiving UF than MF pretreatment over the course of each of four pilot plant runs that lasted from 1 to 7 weeks. The removal of organic matter as measured by dissolved organic carbon (DOC) was somewhat higher by UF than MF pretreatment (about 15% by UF compared with 11% by MF). Addition of ferric chloride ahead of the UF unit, but not ahead of the MF unit, may account for this additional removal of organic matter. However, the additional DOC removal appeared insufficient to explain the differential in foulant accumulation between high-pressure membranes receiving UF and MF pretreatment. Extensive autopsy analyses of these high-pressure membranes showed from 35% to 56% less organic carbon on those receiving UF rather than MF pretreatment. A more specific indicator of a differential in organic fouling was the accumulation of polysaccharides and this showed from 27% to 38% less on UF- than on MF-pretreated membranes. Yet another possible source of foulants is inorganic material given that the inorganic and organic weight percentages were nearly equal (56% vs. 44%) on the membrane surface. One specific source was aluminum added for phosphorus removal. Less fouling of high-pressure membranes pretreated by UF than MF could be due to the following: (1) a small, but very important, colloidal fouling fraction may have passed through MF but was rejected by UF pretreatment; (2) organic fouling was not related to organics in either the MF or UF filtrates but rather to organics that are generated in situ by microbial activity on the membrane surface; and/or (3) less passage of colloidal Al-P that carried over from secondary wastewater treatment.     

MIEX/超滤一体化工艺净化长江原水的研究

水体中的天然有机物是造成超滤膜污染的重要因素。考察了磁性离子交换树脂(MIEX)/超滤膜一体化净水工艺处理长江原水的效果,并通过与超滤膜直接过滤进行比较,探讨了MIEX预处理对去除有机物的影响及控制膜污染的效果。结果表明,与原水直接进行超滤处理相比,组合工艺对CODMn、DOC、UV254的去除率分别提高了40.70%、38.20%和43.90%。MIEX/超滤工艺控制消毒副产物的优势更为明显,对THMFP和HAAFP的去除率分别达62.54%和55.83%。由于MIEX预处理去除了原水中56.72%的疏水性有机物,降低了超滤膜的负荷,延缓了膜表面致密凝胶层的形成,因而减少了膜孔堵塞,可有效控制运行压力的增长速度,延长过滤时间。     

Combination of coagulation and ion exchange for the reduction of UF fouling properties of a high DOC content surface water

The treatment of a high DOC content surface water (about 6mg DOC/L) using anion exchange resins (MIEX resin from Orica or IRA958 resin from Rohm and Haas) can remove up to 80% of DOC in less than 45min. The combination of coagulation prior to or after resin treatment only slightly improves the removal of DOC (0.2-0.3mg/L) but eliminates the high MW organic compounds (MW >20kDa) attributed to biopolymers (proteins and polysaccharides) that were not removed using anion exchange resins alone and that were found to be responsible for reversible fouling of UF membranes (YM 100 UF membrane from Millipore with MW cut-off of 100kDa). The combination of treatments then significantly improves the permeability of the UF membrane. Also, the combination of both treatments allows a reduction of the coagulant doses by a factor of 6 with no impact on the DOC removal and the filterability of produced waters.     

粉末活性炭/污泥回流工艺强化膜前预处理的研究

采用粉末活性炭(PAC)吸附/混凝沉淀/浸没式超滤膜组合工艺处理苏州市某河水,考察了PAC/污泥回流工艺对膜前预处理的强化效果及对膜污染的影响,并与常规混凝沉淀、污泥回流强化混凝沉淀、PAC吸附/混凝沉淀等3种预处理工艺进行了对比。结果表明,PAC/污泥回流强化预处理工艺对浊度、DOC、UV254和THMFP的去除率分别为80.2%、47.5%、42.3%和52.3%,均比其他预处理工艺的高,对MW30 ku和MW1 ku有机物的去除效果明显。PAC/污泥回流强化预处理和超滤膜组合工艺对浊度、DOC、UV254和THMFP的去除率分别可达到99.2%、54.1%、47.2%和60.2%;经过15 d的运行,超滤膜的跨膜压差基本保持稳定,而其他预处理工艺虽能在一定程度上减轻膜污染,但无法避免不可逆膜污染的发生。     

Bench-scale testing of a magnetic ion exchange resin for removal of disinfection by-product precursors

The objective of this research was to compare enhanced coagulation with anion exchange for removal of disinfection by-product (DBP) precursors (i.e. natural organic matter (NOM) and bromide). Treatment with a magnetic ion exchange resin (MIEX((R))) was the primary focus of this study. Raw waters from four utilities in California were evaluated. The waters had low turbidity, low to moderate organic carbon concentrations, a wide range of alkalinities, and moderate to high bromide ion concentrations. The treated waters were compared based on removal of ultraviolet (UV) absorbance, dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), and haloacetic acid formation potential (HAAFP). The results indicated that treatment with MIEX is more effective than coagulation at removing UV-absorbing substances and DOC. Treatment with MIEX and treatment with MIEX followed by coagulation yielded similar results, suggesting that coagulation of MIEX-treated water does not provide additional removal of organic carbon. MIEX treatment reduced the THMFP and HAAFP in all waters, and did so to a greater extent than coagulation. Treatment with MIEX was most effective in raw waters having a high specific UV absorbance and a low anionic strength. Following MIEX treatment, subsequent chlorination resulted in a shift to the more brominated THM and HAA species as compared to chlorination of the raw water. MIEX also removed bromide to varying degrees, depending on the raw water alkalinity and initial bromide ion concentration.     

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.     

Degradation of natural organic matter by TiO2 photocatalytic oxidation and its effect on fouling of low-pressure membranes

Natural organic matter (NOM) fouling continues to be the major barrier to efficient application of microfiltration (MF) and ultrafiltration (UF) in drinking water treatment. In this study, the potential of TiO2/UV photocatalytic oxidation to control fouling of membranes by NOM was evaluated. Decomposition kinetics of NOM was investigated using a commercial TiO2 catalyst, and the effect of various experimental parameters including TiO2 dosage and initial total organic carbon (TOC) concentration were also determined. The reaction kinetics was found to increase with increasing TiO2 dosage, but decrease with increasing initial TOC concentration. Even though the rate of TOC removal was relatively low, the TiO2/UV process was very effective in controlling membrane fouling by NOM. At a TiO2 concentration of 0.5 g/L, fouling of both an MF and a UF membrane was completely eliminated after 20 min of treatment. Careful analyses of specific UV absorbance (SUVA) and molecular weight (MW) distribution of NOM revealed that the effectiveness in membrane fouling control is the result of the changes in NOM molecular characteristics, namely MW and SUVA due to the preferential removal and transformation of large, hydrophobic NOM compounds. Results from this study show that TiO2/UV photocatalytic oxidation is a promising pretreatment method for MF and UF systems.     

Cost factors and chemical pretreatment effects in the membrane filtration of waters containing natural organic matter

This paper compares the membrane processes available for water treatment. Membranes have the advantage of currently decreasing capital cost, a relatively small footprint compared to conventional treatment, generally a reduction in chemicals usage and comparably low maintenance requirements. Three membrane processes applicable to water treatment, micro- (MF), ultra- (UF), and nanofiltration (NF), are compared in terms of intrinsic rejection, variation of rejection due to membrane fouling and increase in rejection by ferric chloride pretreatment. Twelve different membranes are compared on the basis of their membrane pore size which was calculated from their molecular weight cut-off. A pore size of < 6 nm is required to achieve substantial (> 50%) organics removal. For a fouled membrane this pore size is about 11 nm. UV rejection is higher than DOC rejection. Coagulation pretreatment allows a higher rejection of organics by MF and UF and the cut-off criterion due to initial membrane pore size is no longer valid. A water quality parameter (WQP) is introduced which describes the product water quality achieved as a function of colloid, DOC and cation rejection. The relationship between log (pore size) and WQP is linear. Estimation of membrane costs as a function of WQP suggests that open UF is superior to MF (similar cost at higher WQP) and NF is superior to tight UF. Chemical pretreatment could compensate for the difference between MF and UF. However, when considering chemicals and energy costs, it appears that a process operated at a higher energy is cheaper at a guaranteed product quality (less dependent on organic type). This argument is further supported by environmental issues of chemicals usage, as energy may be provided from renewable sources.     

Performance of selected anion exchange resins for the treatment of a high DOC content surface water

The objective of this study was first to compare the performance of four strong anion exchange resins (AERs) (MIEX from Orica Pty Ltd, DOWEX-11 and DOWEX-MSA from DOW chemical and IRA-938 from Rohm and Haas) for their application in drinking water treatment (natural organic matter (NOM), mineral anions (nitrate, sulfate and bromide) and pesticide removal) using bench-scale experimental procedures on a high DOC content surface water. The efficiency of MIEX for NOM and mineral anions removal was furthermore evaluated using bench-scale dose-response experiments on raw, clarified and post-ozonated waters. NOM removal was assessed using the measurement of dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254) and the use of high-performance size exclusion chromatography with UV (HPSEC/UV) and fluorescence detection (HPSEC/FLUO). The MIEX and IRA938 anionic resins exhibit a faster removal of NOM and mineral anions compared to the DOWEX11 and MSA AERs. All the resins were found to be very effective with similar performances after 30 to 45 min of contact time. As expected, only limited sorption of atrazine and isoproturon (C0=1 microg/L) occurred with MIEX, DOWEX11 and MSA AERs. MIEX resin proved to be very efficient in eliminating NOM of high-molecular weight but also a large part of the smallest UV absorbing organic compounds which were refractory to coagulation/flocculation treatment. Remaining DOC levels after 30 min of contact with MIEX were found similar in raw water, clarified water and even post-ozonated water implying no DOC benefit can be gained by employing conventional treatment prior to MIEX treatment. Removal of bromide (initial concentration 110 microg/L) was also observed and ranged from 30% to 65% for resin dose increasing from 2 to 8 mL/L. T     

PAC/PS预处理对水中镉的去除及UF膜污染控制

采用粉末活性炭耦合过硫酸盐(PAC/PS)作为超滤的预处理工艺,考察其对原水中镉和天然有机物的去除效果,以及对超滤膜污染控制的影响。结果表明,对于镉超标6倍的原水水样,当PAC和PS投加量分别为30 mg/L和300μmol/L、接触时间为60 min时,UV₂₅₄、DOC和镉的去除率分别可达到91.7%、68.2%和92.7%,镉浓度可降至《生活饮用水卫生标准》(GB 5749—2006)规定的限值(5μg/L)以下;与直接超滤相比,设置PAC/PS预处理工艺后超滤膜比通量提升了50.5%,XDLVO预测模型中胶体污染物-超滤膜相互作用的总界面能降低了75.38%,超滤膜污染减轻。     

Modification of low pressure membranes with carbon nanotube layers for fouling control

Carbon nanotubes (CNTs) with different physiochemical properties were layered onto low pressure membranes and tested for antifouling properties using a natural surface water with high fouling potential. Membranes modified with the largest diameter pristine multi-walled CNTs (MWCNTs) were most effective in controlling membrane fouling, tripling the time it took for the membrane to become noticeably fouled at a CNT loading of 22 g/m². The differences in the structure of CNT layers were an important contributing factor for antifouling properties; scanning electron microscopy imaging showed that large diameter MWCNTs formed homogeneous porous layers across the membrane surface, while less effective, small diameter MWCNTs formed heterogeneous layers. Water quality analysis showed that CNT-membranes constructed with larger diameter CNTs were more effective at removing larger organic macromolecules responsible for fouling from feedwater compared to membranes made with smaller diameter CNTs. This reduced the concentration of foulants reaching the PVDF membrane and thus helped reduce membrane fouling. Beneficial for application, increased loadings of CNTs onto the membrane surface increased resistance to fouling while only slightly reducing the clean water permeability of the modified membranes. Overall, CNT layered membranes were shown to highly resist membrane fouling with potential applications in sustainable water treatment.     

Removal of bromide and natural organic matter by anion exchange

Bromide removal by anion exchange was explored for various water qualities, process configurations, and resin characteristics. Simulated natural waters containing different amounts of natural organic matter (NOM), bicarbonate, chloride, and bromide were treated with a polyacrylate-based magnetic ion exchange (MIEX) resin on a batch basis to evaluate the effectiveness of the resin for removal of bromide. While bromide removal was achieved to some degree, alkalinity (bicarbonate), dissolved organic carbon (DOC), and chloride were shown to inhibit bromide removal in waters with bromide concentrations of 100 and 300 μg/L. Water was also treated using a two-stage batch MIEX process. Two-stage treatment resulted in only a slight improvement in bromide removal compared to single-stage treatment, presumably due to competition with the high concentration of chloride which is present along with bromide in natural waters. In view of the relatively poor bromide removal results for the MIEX resin, a limited set of experiments was performed using polystyrene resins. DOC and bromide removal were compared by treating model waters with MIEX and two polystyrene resins, Ionac A-641 and Amberlite IRA910. The two polystyrene resins were seen to be more effective for bromide removal, while the MIEX resin was more effective at removing DOC.     

Removal of MIB and geosmin using granular activated carbon with and without MIEX pre-treatment

This study assessed the impact of MIEX pre-treatment, followed by either coagulation or microfiltration (MF), on the effectiveness of pilot granular activated carbon (GAC) filters for the removal of the taste and odour compounds, 2-methylisoborneol (MIB) and geosmin, from a surface drinking water source over a 2-year period. Complete removal of MIB and geosmin was achieved by all GAC filters for the first 10 months, suggesting that the available adsorption capacity was sufficient to compensate for differences in dissolved organic carbon (DOC) entering the GAC filters.Reduction of empty bed contact time (EBCT), in all but one GAC filter, resulted in breakthrough of spiked MIB and geosmin, with initial results inconclusive regarding the impact of MIEX pre-treatment. MIB and geosmin removal increased over the ensuing 12 months until complete removal of both MIB and geosmin was again achieved in all but one GAC filter, which had been pre-chlorinated. Autoclaving and washing the GAC filters had minimal impact on geosmin removal but reduced MIB removal by 30% in all but the pre-chlorinated filter, confirming that biodegradation impacted MIB removal. The impact of biodegradation was greater than any impact on GAC adsorption arising from DOC differences due to MIEX pre-treatment. It is not clear whether, at a lower initial EBCT, MIEX pre-treatment may have impacted on the adsorption capacity of the virgin GAC.The GAC filter maintained at the longer EBCT, which was also pre-chlorinated, completely removed MIB and geosmin for the period of the study, suggesting that the greater adsorption capacity was compensating for any decrease in biological degradation.     

Long term case study of MIEX pre-treatment in drinking water; understanding NOM removal

Removal of natural organic matter (NOM) is a key requirement to improve drinking water quality. This study compared the removal of NOM with, and without, the patented magnetic ion exchange process for removal of dissolved organic carbon (MIEX DOC) as a pre-treatment to microfiltration or conventional coagulation treatment over a 2 year period. A range of techniques were used to characterise the NOM of the raw and treated waters. MIEX pre-treatment produced water with lower concentration of dissolved organic carbon (DOC) and lower specific UV absorbance (SUVA). The processes incorporating MIEX also produced more consistent water quality and were less affected by changes in the concentration and character of the raw water DOC. The very hydrophobic acid fraction (VHA) was the dominant NOM component in the raw water and was best removed by MIEX pre-treatment, regardless of the raw water VHA concentration. MIEX pre-treatment also produced water with lower weight average apparent molecular weight (AMW) and with the greatest reduction in complexity and range of NOM. A strong correlation was found between the VHA content and weight average AMW confirming that the VHA fraction was a major component of the NOM for both the raw water and treated waters.     

Bicarbonate-form anion exchange: affinity, regeneration, and stoichiometry

Magnetic ion exchange (MIEX) is an effective process for removing dissolved organic carbon (DOC) from natural waters, but its implementation has been limited due to production of waste sodium chloride solution (i.e., brine) from the regeneration process. Chloride is of concern because elevated concentrations can have adverse effects on engineered and natural systems. The goal of this research was to explore the efficacy of using anion exchange resin with bicarbonate as the mobile counter ion, which would produce a non-chloride regeneration solution. It was found that bicarbonate-form MIEX resin had a similar affinity as chloride-form MIEX resin for sulfate, nitrate, DOC, and ultraviolet-absorbing substances. Both bicarbonate-form and chloride-form MIEX resins showed the greatest removal efficiencies as fresh resin, and removal efficiency decreased with multiple regeneration cycles. Nevertheless, sodium bicarbonate solution was as effective as sodium chloride solution at regenerating MIEX resin. Regeneration of the bicarbonate-form MIEX resin was illustrated by sparging carbon dioxide gas in a water/resin slurry. This regeneration process would eliminate the need for the addition of salts such as sodium chloride or sodium bicarbonate. The stoichiometry of the bicarbonate-form resin revealed that the bicarbonate was deprotonating within the resin matrix leading to a mixture of both carbonate and bicarbonate mobile counter ions. This work makes an important contribution to ion exchange applications for water treatment by evaluating the affinity, regeneration, and stoichiometry of bicarbonate-form anion exchange.     

A pilot-scale evaluation of magnetic ion exchange treatment for removal of natural organic material and inorganic anions

The objective of this research was to evaluate a magnetic ion exchange process (MIEX) for the removal of natural organic material (NOM) and bromide on a continuous-flow pilot-scale basis under different operating conditions and raw water characteristics. The most important operating variable was the effective resin dose (ERD), which is the product of the steady-state resin concentration in the contactor and the regeneration ratio. The raw water employed in this study had a moderate concentration of ultraviolet (UV)-absorbing substances and dissolved organic carbon (DOC), and a low turbidity, alkalinity, and concentration of competing anionic species. Experiments were conducted using the ambient raw water and raw water spiked with bromide, chloride, and sulfate. Substantial removal of UV-absorbing substances and DOC was achieved at ERDs as low as 0.16mL/L. Moderate bromide removal was achieved, depending on the ERD. Increasing the sulfate concentration resulted in decreased removal of UV-absorbing substances, DOC, and bromide. Consistent results were observed between the continuous-flow pilot plant tests and batch equilibrium studies.     

UF膜组件的有机污染及清洗

近年来,超滤（UF）膜组件的污染问题主要集中在有机物污染的范围。利用几种化学药剂对聚砜超滤膜有机污染造成的堵塞的清洗方式进行了试验研究,研究了UF件的有机污染行为及膜组件污染物的去除。实验证明NaClO,H2O2和NaOH对于UF膜的有机污染去除都有一定的效果,其中H2O2的去除效果最好。控制原水的PH值有利于减轻膜污染。同时,以NaOH／NaClO及NaOH／H2O2水溶液相结合的方式对于膜的蛋白质污染的去除也有很好的效果,能够使超滤膜的渗透水通量恢复到初始值。同时还对UF膜的有机污染形成基理进行了分析。     

Adsorption combined with ultrafiltration to remove organic matter from seawater

Organic fouling and biofouling are the major severe types of fouling of reverse osmosis (RO) membranes in seawater (SW) desalination. Low pressure membrane filtration such as ultrafiltration (UF) has been developed as a pre-treatment before reverse osmosis. However, UF alone may not be an effective enough pre-treatment because of the existence of low-molecular weight dissolved organic matter in seawater. Therefore, the objective of the present work is to study a hybrid process, powdered activated carbon (PAC) adsorption/UF, with real seawater and to evaluate its performance in terms of organic matter removal and membrane fouling. The effect of different PAC types and concentrations is evaluated. Stream-activated wood-based PAC addition increased marine organic matter removal by up to 70% in some conditions. Moreover, coupling PAC adsorption with UF decreased UF membrane fouling and the fouling occurring during short-term UF was totally reversible. It can be concluded that the hybrid PAC adsorption/UF process performed in crossflow filtration mode is a relevant pre-treatment process before RO desalination, allowing organic matter removal of 75% and showing no flux decline for short-term experiments.     

Combination of ferric and MIEX for the treatment of a humic rich water

Seasonal periods of high rainfall have been shown to cause elevated natural organic matter (NOM) loadings at treatment works. These high levels lead to difficulties in removing sufficient NOM to meet trihalomethane (THM) standards, and hence better alternative treatments are required. Here the removal of NOM was investigated by a new ion exchange process (MIEX) using both bulk and fractionated NOM. Initial results showed that in excess of 80% of the raw water dissolved organic carbon (DOC) and greater than 85% of the UV absorbance from the bulk raw water could be removed by the use of MIEX alone. It was also seen that the removal of the more recalcitrant isolated fractions was increased. When MIEX was combined with a significantly reduced dose of coagulant a slight improvement on the overall DOC and UV removals was observed, however a significant decrease in the amount of THM formation potential (THMFP) in the final water was seen. This combined with the reduction in coagulant would imply a more efficient process during the times when the water becomes increasingly difficult to treat.