Microbial community in seawater reverse osmosis and rapid diagnosis of membrane biofouling

Due to the acceleration of global warming and the stress that population growth has placed on the global water supply, seawater reverse osmosis (SWRO) desalination is arising as a promising technology to overcome the stress placed on current water resources. However, the biofouling of RO membranes is a common problem, as it causes flux decline, demands frequent cleanings, and consumes high energy, resulting in a shortened lifespan of the system. In an attempt to address these issues, detailed knowledge of the microbial bacteria present, which have a strong correlation between biofilm community structure and operational problems, is ultimately expected to lead to greater control of biofouling. Furthermore, a more rapid diagnosis of biofilm bacteria in SWRO processes is required for faster process feedback. In this study, previous approaches that have been proposed for understanding, diagnosing, and predicting biofouling are reviewed. Finally, the future outlook towards controlling biofouling in SWRO is discussed.     

Boron in seawater and methods for its separation — A review

The seawater reverse osmosis (SWRO) membrane desalination process is a relevant and reliable technology for desalination of seawater. However, some serious limitations had recently been discovered during field practice, among them the boron problem seems to have a critical meaning. According to the WHO regulations, the boron concentration should be reduced to less than 0.5 mg/L for drinking water. It was also reported that, this limit is rarely reached for conventional reverse osmosis desalination plants equipped with commercially available membranes. This paper reviews the extensive published literature on separation methods of boron removal from seawater.     

A comparative study for boron removal from seawater by two types of polyamide thin film composite SWRO membranes

In this paper, field performance of a small-scale seawater reverse osmosis unit installed in Urla Bay-Izmir, Turkey was analyzed and presented. The design of SWRO system in Urla consists of two types of FilmTec polyamide thin film composite spiral wound seawater reverse osmosis membranes (high rejection FILMTEC XUS SW30XHR-2540 RO membrane and FILMTEC SW30-2540 RO membrane) which could be operated in parallel. To make a comparative study between two types of membranes regarding their desalination performances and boron rejections, each membrane was operated individually for each set of experiments. This comparison was made via investigation of the effects of feed seawater temperature (10–16 °C), operating pressure (55, 60 and 62 bar), and pH adjustment on the feed side (pH 7.0–7.5).     

Global optimality of RO seawater desalination networks with permeate reprocessing and recycle

In conjunction with the optimality of single-stage reverse osmosis (SRO) system, this work addresses the economic competence of prominent seawater desalination reverse osmosis systems with permeate reprocessing and recycle using differential evolution as global optimization tool. The optimization approach refers to nonlinear programming formulation consisting of mass balances and design specifications as equality constraints and other design specifications as inequality constraints. Further, MATLAB optimization toolbox-based analysis was conducted to compare the obtained solutions with deterministic optimization methods. Among all considered alternatives such as two stages reverse osmosis (TRO) series arrangement with retentate reprocessing and permeate recycle (TRO-TSRR-PR), SRO, TRO series arrangement with permeate bypass and permeate reprocessing and TRO with permeate reprocessing series arrangement processes, TRO-TSRR-RP process configuration has been evaluated to competitive with the SRO process with an optimal cost of 0.9527$/m³ obtained with DE-SQP. While the SRO remains the simplest cost-effective system in terms of topological complexity, the TRO-TSRR-PR process has been evaluated to be 5.75% better than the optimal freshwater production cost of SRO process reported in the literature with an optimal decision variable set values [68.51 bar, 7688, 5881.7 m³/h, 259.8 ppm, 2422, 322.9 m³/h and 1764.9 ppm] for [P₁^F, NM₁, W_RO^RF, C₁^RP, NM₂, W₂^RP, C₂^RP].     

Boron removal from seawater using high rejection SWRO membranes — impact of pH, feed concentration, pressure, and cross-flow velocity

The main objective of this work was to investigate boron removal from seawater using two commercial high rejection SWRO membranes. The impact of solution pH, feed concentration, pressure, and cross-flow velocity on boron rejection and permeate flux was determined. The membranes used were the Toray™ UTC-80-AB and Filmtec™ SW30HR. A lab-scale cross-flow flat-sheet configuration test unit was used for all RO experiments. Seawater sample was collected from the Mediterranean Sea, Alanya-Kızılot shores, south Turkey. For all experiments, mass balances were between 91% and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Operation modes did not have any impact on boron rejection, indicating that boron rejection were independent of feedwater boron concentrations up to 6.6 mg/L. For both membranes, much higher boron rejection were obtained at pH of 10.5 (>98%) than those at original seawater pH of 8.2 (about 85–90%). Permeate boron concentrations less than 0.1 mg/L were easily achieved at pH 10.5 by both membranes. The dissociated boron species are dominant at this pH, thus both electrostatic repulsion and size exclusion mechanisms are responsible for the higher boron rejection. The rejection of salts in seawater did not correlate with boron rejection at constant conditions. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5, which may be partially explained by membrane fouling and enhanced scale formation by Mg and Ca compounds from concentration polarization effect at higher pH values. While somewhat higher boron rejection was found for one membrane type as the pressure was increased from 600 to 800 psi, increasing pressure did not affect boron rejection for the other membrane. Feed flowrate thus the cross-flow velocity (0.5–1.0 m/s) did not exert any significant impact on boron rejection at constant conditions.     

废旧反渗透膜循环再利用研究现状与进展

随着反渗透（RO）技术在水处理领域的广泛应用,全球每年有数百万计的废旧RO膜组件作为垃圾被处理处置,由此造成了环境污染与资源浪费。本文首先综述了废旧RO膜可能的循环再利用方案和相关的应用案例,为了比较不同循环方式对环境的影响,概述了通过全生命周期分析（LCA）的方法评价不同循环利用方式的环境效益和物质投入的研究进展。文章指出研究结果表明：回收利用废旧RO膜是研究RO膜末端处理的方法之一,其中包括通过使用清洗后的RO膜作为新生RO膜直接再利用、通过化学转化为其他多孔膜材料再循环使用、通过清洗RO膜拆解回收RO膜。另外,LCA在膜工艺中的分析仍以评估使用过程为主,而缺少在膜设计、膜改造和膜回收等关键过程的分析研究。     

Experimental studies on dynamic process of energy recovery device for RO desalination plants

A two-chamber hydraulic energy recovery unit with a programmable controller and a data acquisition system was set up. Tap water was used as the working fluid instead of the actual seawater and concentrate in SWRO desalination plants. Experimental results were obtained on the fluctuations of the pressure and flow rate to and from the energy recovery unit. Characteristics of the pressure at the chamber ends were discussed at the conditions of the chambers set horizontally or vertically, with and without pistons.     

Feed water pretreatment in RO systems: unit processes in the middle east

The paper deals with the conventional physical, chemical and biological unit processes that are widely applied in the Middle East for treating feedwater to reverse osmosis (RO) systems which produce potable water from brackish groundwater and saline seawater. Depending on the quality of intake water, membrane process, posttreatment and desired quality of product water, a pretreatment system was designed. Such a system usually comprises a train of unit processes based on technical and cost considerations. Proper decision for selecting unit processes involves a thorough evaluation of available alternatives. Results of previous experiences and present guidelines and schemes that are developed combining unit processes for pretreatment of RO feed are reviewed. Through the process, the combination of pretreatment units is made in such a way so that the quality of feedwater is improved at a minimal cost for pretreatment and with minimal adverse effects on succeeding processes: membranes, storage and supply systems. Conceptual layouts of several such systems of alternatives are presented along with comparative data on expected system performance and cost.     

High recovery system in seawater reverse osmosis plants

Seawater desalination by the reverse osmosis (RO) method is an energy-saving system compared with the evaporating method, and can perform seawater desalination efficiently. Seawater RO desalination technology has been established and become a reliable system. Seawater desalination plants using RO technology have spread and the scale of the plants has increased significantly. More economical and efficient RO method seawater desalination systems have come to be required. A high recovery system, which offers reduction of plant construction cost and running cost was devised. Towards realization of this high recovery system, simulation and the field tests were done to confirm the practicality. Furthermore, a high recovery system was adopted for the biggest desalination plant in Japan, and it is performing favorably. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

反渗透膜用阻垢剂的实验室评价

针对内蒙古某污水厂结硫酸钙垢的水质,利用实验室反渗透评价装置对几种国内外膜用阻垢剂进行了阻硫酸钙垢的实验室评价.研究了在一定实验条件下不同类型的阻垢剂对膜通量产生的影响,并找出膜通量随药剂浓度变化的一些规律,为现场实际运行起到了良好的指导作用.     

海水反渗透淡化技术的分析与探讨

反渗透海水淡化技术是一种高效、节能、先进的液体分离技术.论述了目前国内外海水反渗透淡化技术的应用现状,着重介绍了反渗透膜材料及特点、膜污染及清洗、典型的海水反渗透淡化流程,探讨了反渗透海水淡化技术目前存在的问题及未来发展趋势.     

压力交换式能量回收器在反渗透海水淡化技术中的应用

在反渗透海水淡化系统中，高压系统中采用压力交换式能量回收器，大大地降低海水淡化的能耗。压力交换式能量回收器的能量回收效率达到95％以上，本文从其工作原理和反渗透海水淡化设计上阐述其应用的优点。     

海水反渗透淡化用带流体切换器的能量回收设备

Energy recovery device （ERD） is an important part of the seawater reverse osmosis （SWRO） desalination system. There are principally two kinds of ERDs, the centrifugal type and the positive displacement （PD） type. The PD type is of extensive concern and is preferred in large-scale plants. In this article, an innovative fluid switcher was presented and a two-cylinder hydraulic energy recovery unit with a lab-scale fluid switcher was set up. Tap water was used as the working medium instead of the actual seawater and brine in SWRO desalination plants. Under steady state operating conditions, the experimental results were obtained on the variations of the pressure and flow rate to and from the energy recovery unit. The hydraulic recovery efficiency （En） of the energy recovery unit with the fluid switcher reached up to 76.83%.     

Multi-functional forward osmosis draw solutes for seawater desalination

Forward osmosis (FO), as one of the emerging desalination technologies, has the potential to produce freshwater from a variety of water sources by utilizing the osmotic pressure gradient across a semi-permeable membrane. Drawsolution, as an essential component of any FO process, can extract watermolecules fromseawater orwastewater. An ideal draw solution should meet three essential requirements, namely high osmotic pressure, low reverse flux, and facile regeneration mechanism. The selection of proper draw solutes is especially critical for an energy-efficient FO process since the energy consumption mostly arises from the separation or regeneration of the draw solution. Recently, we developed a few multi-functional FO draw solutes, mainly aiming to enhance the FO water flux and to explore facile re-concentration methods. This review summarizes these draw solutes, including Na⁺-functionalized carbon quantum dots, thermoresponsive copolymers, hydrophilic magnetic nanoparticles, and thermoresponsive magnetic nanoparticles.     

反渗透_+一级除盐系统中除碳器设置问题探讨

在反渗透+一级除盐系统中,反渗透出水中HCO3-及CO2含量分别决定除碳器的具体设置位置及是否设置除碳器,其结果影响到系统运行的经济性。对不同设置方式的系统进行分析,分别得出经济平衡点的HCO3-临界值和CO2临界值,确定反渗透+一级除盐系统中除碳器的具体设置位置及设置与否,为电厂水处理设计提供借鉴。     

Bench-scale evaluation of seawater desalination by reverse osmosis

In bench-scale tests of seawater reverse osmosis desalination it is important to carefully consider osmotic pressure effects and determine the extent of concentration polarization so that sources of flux variation—whether from fouling, compaction, or osmotic pressure changes—can be properly assessed. Rigorous modeling of concentration polarization is difficult because of the complex geometries and flow regimes in RO modules; typically, concentration polarization must be measured. However, concentration polarization measurement usually requires knowledge of membrane permeability, which can vary from coupon to coupon. In this study a method is presented to determine both the membrane permeability and the concentration polarization regime in a single test. The key to the test is to allow the salt concentration to vary over time in a predictable way and extract parameters from a model fitted to the flux data. The usefulness of this technique is highlighted by evaluating results from several seawater experiments. It was found that specific flux decline in the experiments was caused by changes in osmotic pressure and membrane compaction. RO fouling by seawater organic-matter was not significant for the several seawater samples tested.     

The analysis and design of a both open ended hollow fiber type RO module

The use of seawater desalination plants using RO technology has spread and the scale of the plants has increased. In such a situation, a larger‐sized RO module has been strongly required. The conventional hollow fiber type RO element is a single open‐ended (SOE) structure. That is, one side of the hollow fibers in the modules is opened and the other side is closed. In this SOE structure, the increase in the flow pressure loss of the permeated water which flows in the bore side of the hollow fibers prevents development of a large‐sized (longer) RO element. In this work, a both open‐ended (BOE) element was devised which can reduce the flow pressure loss of the permeated water. It has been confirmed by analysis and experiment that the permeate flow rate of BOE is greater by about 30% than that of SOE. Furthermore, the large‐sized RO module with high volume efficiency was designed using the performance analysis method that was confirmed to be applicable to BOE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of different operation pressures for various membranes on the performance of RO plants

The aim was to study the effect of different operation pressures on the performance of reverse osmosis (RO) plants for various types of membranes. The study was conducted in a pilot plant at the University of Basrah, College of Engineering, which has a capacity of 9 m³/h. The plant is comprised of two parallel vessels containing five elements for each vessel, 8″ in diameter and 40″ in length. The first vessel has Saehane membranes, type RE8040BE-400 ft² manufactured in South Korea. Koch membranes, type 8822-XR-365 ft² made in the US, were used in the second vessel. The pilot plant uses brackish water from the Tigris River with TDS <600 ppm. The new type of RO membranes (Saehane) were used for the first trial for production of desalted water from brackish water less than 600 ppm and the results were compared with performance of the Koch membranes. It was found that over 180 days of continuous operation, the amount of permeate for Saehane membranes is larger than Koch membranes by about 26%. It was also observed that the quality of permeate water stream for Koch membranes is less than for the Saehane membranes by about 11%.     

Optimal design of reverse osmosis‐based water treatment systems

We address the problem of optimal design of reverse osmosis (RO)‐based water treatment systems. A superstructure optimization method is proposed to solve the problem, where the superstructure for a RO system is structurally enhanced with additional features. We formulate the problem as mixed‐integer nonlinear program which is solved to yield optimal results. A case study on desalination is considered in this work, and the numerical results obtained using our approach are validated using a commercial simulation tool. We further extend the problem by considering the effects of degradation of membrane performance over time and solve it by representing the problem as a two‐stage stochastic program. This new approach is highly useful for identifying minimum cost robust designs for membrane‐based water purification systems, which are especially important in desalination applications. © 2012 American Institute of Chemical Engineers AIChE J, 2012