反渗透膜污染成因与防治

反渗透膜的污染受膜自身性质、水质和操作条件的影响。综述了膜材料、膜结构和膜组件、操作温度、压力、pH值、剪切速率和水质对反渗透膜污染的研究现状,同时指出研制低／抗污染膜和膜组件,优化操作条件．增设水质预处理和有效的膜清洗是皈渗透膜技术的发展方向。     

Preozonation Effects on the Reduction of Reverse Osmosis Membrane Fouling in Water Reuse

The purpose of this bench-top study was to demonstrate the feasibility and effect of applying ozone and ozone/peroxide upstream of reverse osmosis (RO) membranes as a means of controlling organic fouling during reuse applications. A series of ozone or ozone/peroxide doses was applied to surface water and a membrane bioreactor (MBR) filtrate using a HiPOx® reactor skid, with ozone-to-dissolved organic carbon ratios of approximately 0.25 to 1.75. Results from the flat-sheet testing indicate that both ozone- and ozone/peroxide-treated waters, even at the lowest ozone dose of 1.5 mg/L, fouled the membranes less than the MBR filtrate and surface control waters while both treated and control waters maintained consistent levels of salt rejection throughout the tests.     

反渗透膜污染成因与防治

反渗透膜的污染受膜自身性质、水质和操作条件的影响.综述了膜材料、膜结构和膜组件、操作温度、压力、pH值、剪切速率和水质对反渗透膜污染的研究现状,同时指出研制低/抗污染膜和膜组件,优化操作条件.增设水质预处理和有效的膜清洗是反渗透膜技术的发展方向.     

Rotating reverse osmosis for water recovery in space: influence of operational parameters on RO performance

Rotating reverse osmosis (RO), which is based on Taylor-Couette flow, offers a means to minimize flux decline due to concentration polarization and membrane fouling. However, the operating conditions play a significant role in determining the effectiveness of the system. In this study, the effect of operating conditions on system performance was explored using a theoretical model. Flux, rejection, recovery, and theoretical power consumption were calculated for a wide variety of operating parameters including transmembrane pressure, rotational speed, and concentrate flow rate. Flux and rejection increase with increasing transmembrane pressure and rotational speed. Operating in the vortical flow regime enhances the filtration performance. Higher concentrate flow increases flux, but decreases recovery. The power consumption for rotating RO is similar to that for conventional RO except at very high rotational speeds.     

Fouling of cellulose acetate tubular reverse osmosis modules treating the industrial water in Tokyo

The Tokyo industrial water supply was treated in tubular reverse osmosis modules in order to investigate the effect of feed velocity and type of membrane on fouling. Rate of fouling by mechanical compaction was proportional to time, whose power was dependent on the initial flux of membrane, while fouling by the deposit of suspended solids tended to cease after the flux was down to a certain value, which was dependent on the feed velocity. Results were analysed by the deposit accumulation model. The deposit layer had a salt-rejecting ability, and its permeability was calculated.     

Optimising operation of an integrated membrane system (IMS) — A Box–Behnken approach

The optimum operating conditions of an integrated membrane system (IMS), consisting of microfiltration (MF) followed by reverse osmosis (RO), has been defined using Box–Behnken design associated with generalised linear models (respectively quasibinomial logit analysis for the MF process and quasibinomial probit analysis for the RO process). Parameters studied for the MF process were the flux, backwash frequency and chloramine dose and dosing point. Parameters studied for the RO were the flux, recovery, pH and antiscalant dose. For both processes, the statistical method successfully determined an envelope of operating conditions. Results showed MF membrane fouling propensity to be mainly controlled by backwash frequency and flux, whereas fouling of the RO membrane was primarily defined by the pH and the recovery. The model was found to accurately represent the plant performance within the operating envelope studied.     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

The use of reverse osmosis for the treatment of Rhine river water. Part I

This paper describes the experience of 19 months operation of a 16 m³/d reverse osmosis pilot plant operating under practical conditions on a highly polluted source (Rhine river). The main problem is the flux decline due to membrane fouling. The results represent the effect of parameters such as feed water quality and pretreatment, temperature, brine velocity and membrane quality. Using simple cleaning techniques, an essential constant production rate could be maintained during the 19 month test period, and membrane compaction was found to be negligible.     

抗污染芳香聚酰胺反渗透膜研究进展

聚酰胺反渗透膜具有选择透过性高、化学稳定性好等优点,在水处理领域应用广泛。但膜污染导致的通量下降、寿命降低等问题严重制约了其发展与应用,开发抗污染反渗透膜是缓解膜污染的重要手段。本文根据抗污染膜作用机理将抗污染反渗透膜分为抗黏附型、污染驱除型和杀菌型,综述了近年来相关方面的研究成果,并对合理组合多种机制制备抗污染反渗透膜的进展进行简要概括,最后对抗污染反渗透膜的发展前景进行了展望。     

Dendritic molecules give excellent long-lasting desalination fouling resistance to reverse osmosis membrane by generating an amine-rich layer

The organic fouling of polyamide membranes is one of the most serious problems in reverse osmosis fields such as sea water desalination and sewage disposal. In this study, poly(ethylene imine)–poly(ethylene glycol) dendrimer is used to improve the fouling resistance of polyamide reverse osmosis membranes. A crucial pretreatment is carried out with a reaction between poly(ethylene imine) and acyl chloride on the nascent polyamide surface, generating an amine-rich selective layer. Poly(ethylene glycol) diglycidyl ether is then attached to the primary amine group. The results illustrate a remarkable improvement in membrane surface hydrophilicity after modification (the contact angle decreases from 96.7° to 49.5°). Dynamic fouling tests are implemented with bovine serum albumin as a typical protein foulant, in which the membranes show very low protein adsorption (flux recovery ratio 96.9%). After 11-cycle fouling tests, the membranes show excellent long-term stability and remarkable antifouling property and cleaning performance. This approach of grafting a dendrimer might provide new insight for antifouling modifications for membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47368.     

Performance evaluation of pretreatment processes in integrated membrane system for wastewater reuse

A series of lab-scale filtration experiments were performed under various operating conditions to investigate the fouling behavior of microfiltration (MF) membranes when employing two different pretreatment methods. The secondary effluents from a biologically advanced treatment process were fed to each hybrid system, consisting of coagulation-flocculation-MF (CF-MF) and ozonation-MF processes. All experiments were carried out using a stirred-cell system, which consisted of polyvinylidene difluoride (PVDF) MF membranes with a 0.22 μm pore size. When MF membrane was used alone without any pretreatment, the permeate flux dropped significantly. However, in the case of employing polyaluminium chloride (PACl) coagulation and ozonation as a pretreatment, the extent of flux decline rates was enhanced up to 88 and 38%, respectively. In the CF-MF hybrid system, the removal efficiencies of COD and total phosphorus were significantly enhanced at a coagulant dose above 30 mg/L. With ozonation, more than 90% of the color was removed even at a low dosage of ozone (5 mg/L). Therefore, ozonation would be strongly recommended as a pretreatment in terms of removing organic matter. The permeate water quality by ozonation-MF process was in good compliance with the guidelines for wastewater reuse proposed by South Korean Ministry of Environment.     

Advanced reverse osmosis process with automatic sponge ball cleaning for the reclamation of municipal sewage

These experiments were conducted with secondary effluent from the terminal plant at Osaka, Japan, in order to determine the potential of the sponge ball cleaning system as an advanced reverse osmosis membrane cleaning technique. It was confirmed that sandfiltration of the feed as a method for reverse osmosis pretreatment and the use of chemical cleaning reagents to restore flux levels were unnecessary, when sponge ball cleaning was used.As a result, the product water flux was maintained at 0.65 ～ 0.75m³/m² day at 25°C and membrane rejection was more stable. No damage to the membrane, which would mean a decline of rejection ability, was recognized by scrubbing of the membrane surface by sponge rubber balls.It was confirmed that tight membranes were more suitable than loose ones because firstly it was easier to remove membrane fouling, secondly the product flux was nearly equal, and finally the product water was of better quality.     

Catalytic ozonation of thymol in reverse osmosis concentrate with core/shell Fe3O4@SiO2@Yb2O3 catalyst:Parameter optimization and degradation pathway

In this work, a novel catalyst of Fe_3O_4@SiO_2@Yb_2O_3 was prepared and the degradation of thymol in reverse osmosis concentrate using ozonation was explored. The operational parameters, such as ozone dosage(8–48 mg·min~(-1)),initial thymol concentration(20–100 mg·L~(-1)), initial pH value(3–11), and catalyst Fe_3O_4@SiO_2@Yb_2O_3dosage(0.2–1.0 g), were studied focusing on the thymol degradation and COD removal. The results indicated that the increase in ozone dosage, initial p H value, and Fe_3O_4@SiO_2@Yb_2O_3dosage accelerated the thymol degradation and COD removal, while the increase in initial thymol concentration hampered the effect of ozonation. A pathway of thymol degradation by catalytic ozonation was proposed based on the intermediates detected by gas chromatography-mass spectrometer and ion chromatography. This paper can provide basic data and technical alternative for pollutant removal from reverse osmosis concentrate by ozonation.     

Silica and metals removal by pretreatment to prevent fouling of reverse osmosis membranes

Reverse osmosis is being increasingly used for desalination of seawater, brackish water and as well the marginal and polluted wastewaters. The operation of waters bearing substantial amount of silica is only feasible if there is a chemical pretreatment in process to prevent excessive and unbearable fouling by this refractory deposit. In this study, model solutions representing tailings wastewater which usually has high silica content was used in standard jar tests using the Boltac Coagulation and Flocculation simulator to determine the effectiveness of chemical pretreatment (by precipitation and coagulation) for removal of silica and other species such as magnesium, calcium, iron and manganese which affect silica fouling. Two precipitants were tested: lime and soda ash, and caustic soda. Precipitant aids (alum and ferric chloride) were also examined in combination with optimum precipitant doses to observe their differential effects. The optimum precipitant dose of caustic soda was 200 mg/L. Ferric chloride and alum were tested with this optimum caustic soda dose, but did not improve removal significantly, if at all. The optimum precipitant dose of lime and soda ash was 150 mg/L lime and 450 mg/L soda ash. Ferric chloride and alum were tested with this optimum lime and soda dose, but again did not improve removal enough to warrant their use. Neither of the methods were as effective in removal of magnesium and calcium as in removal of other components; lime and soda ash treatment as expected actually increased the calcium content of solutions.     

反渗透膜有机污染的研究进展

介绍了反渗透进水中一些主要有机污染物质的污染机理以及操作条件、膜自身特性、溶液化学性质对于污染过程的影响,还综述了预处理技术、清洗方法以及通过膜的表面改性等措施来控制反渗透膜的有机污染,最后指出了目前研究中需关注的一些问题。     

An advanced treatment of high-strength opium alkaloid processing industry wastewaters with membrane technology: pretreatment, fouling and retention characteristics of membranes

This paper presents the results of the laboratory and pilot-scale membrane experiments of opium alkaloid processing industry effluents. Different types of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for membrane fouling, permeate flux and their suitability in separating COD, color and conductivity. Experiments demonstrated that membrane treatment is a very promising advanced treatment option for pollution control for opium alkaloid processing industry effluents. Almost complete color removal was achieved with NF and RO membranes. COD and conductivity removals were also greater than 95% and met the current local standards. Nevertheless, pretreatment was an important factor for the NF and RO membrane applications. Membrane fouling occurred with direct NF membrane applications without UF pretreatment. The total estimated cost of the UF and NF treatment system was calculated as $0.96/m³, excluding the concentrate disposal cost.     

电厂反渗透系统膜污染防治与膜清洗的研究

考察了长期运行的电厂反渗透系统中导致膜污染的原因、膜污染的种类和膜的清洗方法。采用反渗透系统进水和浓水的水质分析数据,提出了判断膜污染原因及污染物组成。根据反渗透系统进水和浓水的水质分析数据,实验筛选了膜清洗剂配方。结果表明表面活性剂对无机、有机混合垢有明显的促溶作用,以0.05%Na-SDS＋0.1%NaOH＋1%Na4-EDTA为配方的清洗剂,其清洗无机、有机混合膜污染的效果良好。     

Synergistic behavior between silica and alginate: Novel approach for removing silica scale from RO membranes

The formation of mineral scale deposits on membranes is a pervasive and expensive problem for the water treatment industry. A series of experiments run on a laboratory-scale reverse osmosis membrane system examined the fouling of membranes when the feed water was spiked with organic and inorganic foulants. Alginic acid was used as the organic foulant and silica was used as the inorganic foulant. Studies involving interactions of these two foulants have not previously been reported in literature. Experiments were run with each foulant individually to characterize fouling at different velocities and pressures. Experiments were then run using both foulants together to characterize the synergistic effects on membrane fouling. One set of experiments with both foulants demonstrated that alginic acid inhibits silica fouling on reverse osmosis membranes. Further experiments indicated that alginic acid added after silica fouling had already occurred was able to remove silica scale from the membrane and restore permeate flux.     

Pilot plant studies on the removal of trihalomethanes by composite reverse osmosis membranes

The effect of single trihalomethane (THM) (CHCl₃) content in various types of water on the performance of two types of reverse osmosis composite membranes (the AFC99 membrane in tubular module B1, PCI, and the FT30 membrane in a spiral-wound element BW3040, FilmTec) have been investigated. The performance of these membranes in RO tests carried out using distilled water, tap water and brackish water (1000–5000 ppm NaCl) with the addition of THM have been evaluated in terms of permeate flux and the rejection of dissolved solids and THM. The FT30 membrane provided THM rejection better than 99.5% during the reverse osmosis treatment of tap water and brackish water. The AFC99 membrane exhibited only 80% retention of THM, obtained for the transmembrane pressures in the range of 10 to 30 bars. It was found that the presence of CHCl₃ slightly affects the transport and separation properties of the composite membranes used.     

Fouling control in activated sludge submerged hollow fiber membrane bioreactors

The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid—liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH₄)₂SO₄ as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mg/L. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.