Organic fouling of RO membranes: Investigating the correlation of RO and UF fouling resistances for predictive purposes

This study examines the characteristics of deposits from dead-end UF and cross-flow RO filtration of dilute mixtures of sodium alginate (SA) and humic acids (HA), which are representative of common foulants in RO and NF feed waters. The data are interpreted in terms of specific cake resistance, α. The presence of alginates in the mixed fouling layers, even in relatively small percentage, imparts characteristic properties to these deposits; i.e. a gel-like structure which is associated with reduced compressibility and permeability. With SA/HA mixtures, high rejection of organic species and high deposition factors are obtained in UF and RO tests, respectively. The specific resistance of mixed SA and HA deposits tends to increase with increasing SA concentration in solution. The resistances α exhibit fairly strong (power law) dependence on the pressure difference across the cake, ΔΡ_c, for both RO and UF tests. The fairly satisfactory correlation of resistance α versus ΔΡ_c data, obtained from both types of tests (for the mixtures of organic species tested at small salinity) is a significant result of this work. Based on this correlation, an approach is suggested for estimating fouling index I and initial membrane fouling rate of a specific RO process, relying on limited UF tests.     

超滤-反渗透用于煤化工回用水处理的工程设计

鄂尔多斯某煤化工厂回用水处理装置主要进水水源为污水处理装置出水、循环水场排污水及脱盐水站的排污水,采用匀质池+高效澄清器+多介质过滤器+超滤及反渗透的组合处理工艺,出水用作循环水场补水。本回用水处理装置已经建成运行近1 a,运行结果表明,装置运行稳定,出水水质达到《污水再生利用工程设计规范》(GB50335—2002)中再生水用作循环冷却系统补充水的水质标准。     

二硫化钼纳米片基水处理纳滤/反渗透膜研究进展

二硫化钼（MoS₂）纳米片的层内固有缺陷以及层间纳米限域通道的存在,有利于提高水处理纳滤/反渗透（NF/RO）膜的渗透选择性。本文首先介绍了MoS₂纳米片的“三明治”结构,其具有易功能化、高吸附容量和氧化还原去除能力、层间纳米限域通道的光滑性和稳定性及抗污染等特性;然后重点综述了MoS₂基纳米孔膜、层叠膜和混合基质膜的制备方法及膜性能的影响因素;最后总结了MoS₂纳米片基水处理NF/RO膜未来发展亟待解决的关键问题,主要包括研究大尺寸纳米片和均匀亚纳米孔的可控制备方法,开发超薄、高度有序的MoS₂分离层构建方法,探索层间纳米限域通道内分子和离子的传输行为和潜在的分离机理,开发增强与聚合物基质界面相容性的改性策略,对下一代高性能水处理NF/RO膜的研发具有启发意义。     

Grey water treatment and simultaneous surfactant recovery using UF and RO process

The membrane-based grey water treatment for grey water reuse and surfactant recovery is presented in this research paper. Grey water from washing machine discharges having turbidity and used surfactant was processed through the polymeric ultrafiltration (UF) membrane to remove the turbidity. The UF treated grey water is further purified by reverse osmosis (RO) membrane for surfactant recovery and water reuse. The surfactant trapped inside the RO spiral wound membrane module is recovered through various membrane physical regeneration techniques such as backwashing, simultaneous backwash–back-flush and ozone back-flush. Among this, backwash–back-flush is found to be effective process for surfactant recovery. The methodology for optimising surfactant recovery is captured by studying effect of various operating parameters such as feed detergent concentration, backwash pressure, backwash temperature and back-flush flow rate. By implementing optimal process conditions, the integrated UF and RO membrane process is able to produce 300 L of reusable pure water and 80 L of concentrated detergent solution and 20 L of turbid water while treating 400 L of grey water discharges. Maximum surfactant recovery of 82% is obtained while treating grey water which consists of 720 ppm of total dissolved solids (detergent) and 45 ppm of surfactant. The extent of UF and RO membrane fouling is determined by measuring the pure water flux before and after the grey water treatment. The membrane performance is found to be stable when membrane is regenerated by backwash–back-flush technique for RO and gravity backwash for UF membrane.     

脱盐水超滤膜反渗透膜的运行管理

超滤作为反渗透预处理,截留了大部分的悬浮物、胶体、有机物等,保证了反渗透装置正常运转。但超滤、反渗透存在膜易污染,易阻塞、氧化等问题,日常运行中加强对超滤反渗透的管理,即可延长膜使用寿命,也可减少污水排放。     

超滤和反渗透在电厂中水回用技术中的应用

对发电厂的中水回用技术方案进行综合比较,为最终方案的确定提供了理论依据.     

Water and solute transport through cellulose acetate reverse osmosis membranes

Reverse osmosis data on two different cellulose acetate membranes using seven organic solutes of varying molecular weight have been obtained.A combined viscous-flow and frictional model is presented and used to estimate the maximum retention, the friction between solute and membrane, the distribution coefficient for solute and the pore radius.The calculated values of the maximum retention and distribution coefficient have been compared with the Ferry-Faxen equation. For the more open membrane these are in good agreement. The tighter one, however, shows a greater interaction between solute and membrane than predicted by the Faxen equation.Some data on two-solute systems are presented and shown to give variation in the retention, which can be explained from the convection term.Furthermore, for experiments with dextran the permeate shows a significant reduction in both $\text{M}$_n and $\text{M}$_t     

Fabrication of PAN/PHCS adsorptive UF membranes with enhanced performance for dichlorophenol removal from water

A series of novel polyacrylonitrile (PAN) adsorptive UF membranes were prepared via the nonsolvent induced phase inversion method using adsorbent‐amphiphilic porous hollow carbonaceous microspheres (PHCSs) as additive. The resulted PAN/PHCS membranes were demonstrated to have better mechanical strength than the pure PAN membrane. The water fluxes of the PAN/PHCS membranes were slightly decrease; however, the rejections to pepsin were maintained at a high level (81–86%). The properties of the PAN/PHCS membranes for 2,4‐dichlorophenol removal from water were investigated. The results showed that 2,4‐dichlorophenol could be rapidly removed from water via adsorption mechanism by PAN/PHCS membranes, and the maximum reduction efficiency was up to 70%. The adsorption of 2,4‐dichlorophenol to the membranes was reversible and the membranes could be regenerated facilely by water washing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40837.     

Evaluation of UF and RO in a cellulose saccharification process

The applications of membrane separation within the bioconversion of lignocellulosic materials to ethanol are studied, and this paper reports on cellulolytic enzyme recovery, and reduction of the product inhibition. The conversion of cellulose and hemicellulose to hexoses and pentoses is carried out in a laboratory scale UF-membrane reactor, and the sugars, which have an inhibiting effect on the enzymes, are continuously removed with the permeate. By optimizing the space velocity, the enzyme inhibition is minimized and the rate of hydrolysis is significantly increased.The recovery of the enzymes has also been investigated with regard to their mechanical stability and adsorption on the substrate. Prior to enzymatic hydrolysis, the raw material is subjected to a pretreatment to make the cellulose more accessible to the enzymes, and the effect of the pretreatment can easily be evaluated in the UF-membrane reactor.As a result of the continuous removal of products formed in the hydrolysis, the permeate has a low content of fermentable sugars, and to give the optimal conditions for the fermentation a concentration step is needed. Different RO-membranes are tested in a laboratory scale batch cell to be able to choose a membrane material, fit for filtration in larger modules.     

Friction coefficient analysis of multicomponent solute transport through polymer membranes

A new analysis is presented of the relations between the multicomponent diffusion coefficients and the classical Kedem–Katchalsky coefficients which describe solute transport in membranes. This analysis is applied to binary and ternary systems and shows the importance of system nonideality in the calculation of solute diffusion coefficients. It is shown that the solute permeability coefficients can be calculated from independent knowledge of the nonideal thermodynamic activity coefficients and the multicomponent diffusion coefficients of the system. © 1996 John Wiley & Sons, Inc.     

双膜法污水处理回用实验研究

UF+RO法也称为双膜法,主要应用于污水的深度处理;实验研究以河北某味精厂污水处理中心二级出水作为原水质,采用UF+RO法进行深度处理,结果表明出水水质达到了该厂回用水质标准。     

Effects of feed water temperature on inorganic fouling of brackish water RO membranes

A bench scale RO process simulator was operated in a batch concentration mode to determine the effects of product water recovery and feed water temperature on flux, rejection, and inorganic fouling by gypsum scale formation for simulated brackish water. As feed water temperature increased, salt rejection and concentration polarization decreased (reducing scale formation potential at a given recovery). However, gypsum crystal nucleation and growth rates increased with temperature. Specifically, at 15 and 25°C gypsum scale formation resulted in slow, steady flux decline at recoveries as low as 10–20%. At these temperatures, many small crystals formed over the entire membrane surface. In contrast, at 35°C flux decline was due to the increasing feed solution osmotic pressure — up to a recovery of about 70%. At this recovery, we observed a sudden, rapid loss of flux and a concomitant spike in feed water turbidity. Relatively few (in number), large crystals formed on the membrane towards the brine outlet of the RO simulator, but the entire membrane surface was covered with “needle-like” crystal fragments. The crystal fragments broke off from growing gypsum rosettes and re-deposited uniformly across the membrane forming a “cake layer” that caused the massive flux decline. These results suggest that high temperature operation of brackish water RO processes could enable higher recovery and lower energy consumption, but operating near the limiting recovery (at elevated temperature) creates an increased risk of a catastrophic fouling event.     

AOP/UF/RO系统在金属表面处理废水回收中的应用

采用AOP＋BAC/UF/RO系统工艺处理金属表面处理废水,构成一整套回收水系统;通过对各项运行参数的分析研究,确定该系统出水水质稳定,且可以连续运;产水水质明显优于自来水水质标准,可被回用到生产线上。     

Processing of black liquors by UF/NF ceramic membranes

This study deals with the treatment of black liquor from wood pulping by means of membranes. UF/NFmembranes with a skin layer of TiO₂ and ZrO₂ have been applied to recover water and to concentrate the residual effluent. Three different membranes with molecular weight cut-off of 1, 5 and 15 kDa have been checked. The membranes have been tested either in single stage operation or in cascade. Total dissolved solids, organic matter, organic to mineral matter ratio and ash have been determined. In addition, chemical oxygen demand (COD) retention was calculated by measuring in the feed solution as well as in the permeate and in the concentrated solution. During the concentration step the steady state was reached after a few minutes running. There was not significant change in the permeate flow until the volume was reduced at half. Only the 15,000 Da membrane showed continuous permeate flow declining. Regardless the membrane used, dry matter, organic matter and COD analyses showed that the retention of organic substances fell in the range of 60-70%, depending on the conditions selected.     

食品饮料行业微滤、超滤、反渗透膜的清洗

本文介绍了食品饮料行业膜过滤装置及配件的清洗     

Modeling of backwash cleaning methods for RO membranes

A new comprehensive and time-dependent 2D model using finite element method (FEM) was developed to account for different versions of the backwash (BW) cleaning method for RO membranes. Two distinct cases of backwash were identified: Case 1, which has no applied pressures and velocities; and Case 2, where inlet velocity and pressure are applied in the feed channel, and in some cases pressure is also applied in the permeate channel. The model was verified by comparing it to existing BW data from both cases. The current 2D model is accurate enough to describe the actual 3D time-dependent BW process. Case 1 reduces to a 1D model agrees with the existing 1D analytical model and was found to be fully predictive. Case 2 deals with reported studies in a 2D format, and is suited to an industrial interest of keeping desalination setup unchanged while activating BW membrane cleaning. Water and salt diffusion coefficients were determined and found to be dependent on feed concentration and applied pressures. Dynamic change of concentration profiles of feed and permeate channels were illustrated. The resulting profiles reveal that in Case 2, changes in feed concentration profiles are negligible, while all other profiles of both cases change substantially with time.     

Fouling of RO membranes in wastewater applications

Organic and inorganic fouling problems associated with reverse osmosis treatment of municipal wastewater were studied at the Advanced Wastewater Treatment facilities at Hoover Dam. This study indicated that the severity of organic fouling can be reduced by improving the quality of the RO feedwater; namely, by removal of food sources for bacterial growth including BOD, TOC, and ammonia. This, besides the normal secondary treatment, required lime softening and filtration. Lime softening and filtration alone, without secondary treatment, were not found to be effective. Chlorination is necessary to discourage bacterial and fungal growth. Where dechlorination is required to protect the membrane, in the case of polyamide membranes for example, sodium bisulfite was found to be superior to sodium thiosulfate. Use of ultraviolet radiation showed promise as an alternate to chlorination for RO feedwater disinfection. Inorganic fouling can be controlled by pretreatment processes including softening and removal of iron and manganese, and by reducing water recovery.