A comparative life cycle assessment of hybrid osmotic dilution desalination and established seawater desalination and wastewater reclamation processes

The purpose of this study was to determine the comparative environmental impacts of coupled seawater desalination and water reclamation using a novel hybrid system that consist of an osmotically driven membrane process and established membrane desalination technologies. A comparative life cycle assessment methodology was used to differentiate between a novel hybrid process consisting of forward osmosis (FO) operated in osmotic dilution (ODN) mode and seawater reverse osmosis (SWRO), and two other processes: a stand alone conventional SWRO desalination system, and a combined SWRO and dual barrier impaired water purification system consisting of nanofiltration followed by reverse osmosis. Each process was evaluated using ten baseline impact categories. It was demonstrated that from a life cycle perspective two hurdles exist to further development of the ODN-SWRO process: module design of FO membranes and cleaning intensity of the FO membranes. System optimization analysis revealed that doubling FO membrane packing density, tripling FO membrane permeability, and optimizing system operation, all of which are technically feasible at the time of this publication, could reduce the environmental impact of the hybrid ODN-SWRO process compared to SWRO by more than 25%; yet, novel hybrid nanofiltration-RO treatment of seawater and wastewater can achieve almost similar levels of environmental impact.     

Nanofiltration in pretreatment of drainage waters of the dumps for solid domestic wastes

The paper has investigated principal technological parameters of nanofiltration of drainage domestic wastes in the village of Velyki Dmytrovychi and the village of Pirogovo, Kiev region. It has been shown that this process may be considered an effective method for the pretreatment of wastewaters in question prior to their after-treatment and desalination with reverse-osmosis making it possible to reduce the contents of organic and mineral impurities in the initial water and thereby to reduce a load on a reverse-osmosis membrane.     

Reverse osmosis desalination: Water sources, technology, and today's challenges

Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.     

Substantiation of flow charts for reverse-osmosis desalting with the ion-exchange softening of sea water and permeate

The article has considered flow charts for the preparation of make-up water of boilers of low, medium, and high pressure (9.8 MPa) from the sea water based on reverse-osmosis desalination. We have proved the possibility of deep Na-cationic softening of permeate by their own concentrates of the desalination stage. Reliable prevention of calcium deposits on membranes is achieved by acidulation of the waters of the Black Sea and Na-(Mg-Na)-zeolite softening process of the Caspian Sea waters also with the use of the concentrate for regeneration of the cation-exchanger.     

反渗透海水淡化脱硼技术研究现状

硼在水中以硼酸的分子形式存在,其浓度过高对农作物和人体会产生不利的影响。由于硼的分子半径小,且不具有电性,因此反渗透海水淡化需要与其他方法相结合才能使硼含量达到饮用水的卫生要求。介绍了目前反渗透海水淡化中的脱硼方法。     

大型反渗透海水淡化系统双端产水脱硼工艺研究

针对大型反渗透海水淡化系统,设计了一种双端产水脱硼工艺,并采用反渗透系统模拟软件研究了二级进水pH值、海水温度和硼含量等参数对工艺脱硼效果的影响。结果表明,该工艺能有效脱除海水中的硼,当二级进水pH值为9. 5时,产水水质可以达标。当海水温度和硼含量均较低时,仅开启一级系统时产水水质即可达标;当海水温度> 13℃或硼含量> 2. 3 mg/L时,需启用二级系统进一步脱硼;当海水温度> 30℃或硼含量> 6. 0 mg/L时,还需适当提高二级进水pH值来增强反渗透膜的脱硼率,以实现产水硼含量达标。与常规脱硼工艺相比,双端产水脱硼工艺通过减少43%的二级系统处理规模,使二级系统的建设投资成本和运行成本均减少43%。     

超滤＋反渗透在净水厂脱盐深度处理的应用

针对水源靠近海边、含盐量（氯化物）较高的实际情况，航丰水厂二期工程采用超滤＋反渗透深度处理工艺，取得较好脱盐效果，水厂出水稳定达标。文章介绍了整个水厂及超滤＋反渗透深度处理工艺流程、设计参数及处理效果，以期更广泛地应用于高含盐水处理工程。     

絮凝—沉淀一体化设备对海水的预处理效果

采用絮凝-沉淀一体化设备对渤海海水进行反渗透海水淡化预处理的试验,考察了该设备的处理效果。当聚合氯化铁（PFC）的投量为5．0mg／L、聚丙烯酰胺（PAM）的投量为3.0mg／L时,在适宜的pH条件下（pH值约为11）,经该设备处理后,出水的浊度〈1.0NTU,SDI值〈4．0,CODMn〈3.0mg／L。出水水质可满足反渗透工艺对进水的水质要求。     

Full-scale simulation of seawater reverse osmosis desalination processes for boron removal: Effect of membrane fouling

The objective of this study is to further develop previously reported mechanistic predictive model that simulates boron removal in full-scale seawater reverse osmosis (RO) desalination processes to take into account the effect of membrane fouling. Decrease of boron removal and reduction in water production rate by membrane fouling due to enhanced concentration polarization were simulated as a decrease in solute mass transfer coefficient in boundary layer on membrane surface. Various design and operating options under fouling condition were examined including single- versus double-pass configurations, different number of RO elements per vessel, use of RO membranes with enhanced boron rejection, and pH adjustment. These options were quantitatively compared by normalizing the performance of the system in terms of E_min, the minimum energy costs per product water. Simulation results suggested that most viable options to enhance boron rejection among those tested in this study include: i) minimizing fouling, ii) exchanging the existing SWRO elements to boron-specific ones, and iii) increasing pH in the second pass. The model developed in this study is expected to help design and optimization of the RO processes to achieve the target boron removal at target water recovery under realistic conditions where membrane fouling occurs during operation.     

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.     

电厂水处理反渗透系统优化研究函数的建立

通过对水处理反渗透系统经济性函数的建立,可供设计者利用反渗透除盐优化计算软件进行优化设计,对反渗透系统的经济性优化提供了计算依据。     

Formation of hazardous inorganic by-products during electrolysis of seawater as a disinfection process for desalination

From our previous study, an electrochemical process was determined to be a promising tool for disinfection in a seawater desalination system, but an investigation on the production of several hazardous by-products is still required. In this study, a more intensive exploration of the formation patterns of perchlorate and bromate during the electrolysis of seawater was conducted. In addition, the rejection efficiencies of the targeted by-products by membrane processes (microfiltration and seawater reverse osmosis) were investigated to uncover the concentrations remaining in the final product from a membrane-based seawater desalination system for the production of drinking water. On the electrolysis of seawater, perchlorate did not provoke any problem due to the low concentrations formed, but bromate was produced at a much higher level, resulting in critical limitation in the application of the electrochemical process to the desalination of seawater. Even though the formed bromate was rejected via microfiltration and reverse osmosis during the 1st and 2nd passes, the residual concentration was a few orders of magnitude higher than the USEPA regulation. Consequently, it was concluded that the application of the electrochemical process to seawater desalination cannot be recommended without the control of bromate.     

超滤预处理工艺在反渗透海水淡化系统中的应用

针对海水淡化工程中的原水水质和出水要求,通过比较各种预处理方式,提出在反渗透海水淡化系统中采用超滤预处理工艺。介绍了超滤预处理工艺的运行参数,并与常规工艺进行了对比。     

Rejection of organic compounds by ultra-low pressure reverse osmosis membrane.

The introduction of ultra-low pressure reverse osmosis (ULPRO) membrane has widened the horizon of reverse osmosis (RO) in purification of surface water and wastewater as well as desalination of brackish water. The ULPRO membrane chemistry can provide a high water flux at low operating pressure, while maintaining a very good salt and organics rejection. This paper deals with the investigation on the rejection of low molecular weight organic compounds by ULPRO membrane. Laboratory scale experiments were carried out at a pressure of 3 kg/cm2 with a feed flow rate of 1.20 l/min. The rejection of undissociated organic compounds did not show a close relationship with the feed pH. The percentage removal of undissociated organic compounds increased linearly with the molecular weight as well as with the molecular width. The removal efficiency can be predicted by these relationships. But neither molecular weight nor molecular width can be considered as an absolute factor for rejection. The feed pH also influenced the removal efficiency of dissociated organic compounds. The efficiency decreased linearly with the increase in the dissociation constant.     

Reducing the environmental impacts of reverse osmosis desalination by using brackish groundwater resources

The aim of the present work is to find out whether or not, and to what extent, the environmental impacts of reverse osmosis desalination are reduced when brackish groundwater is used instead of sea water. In order to answer this question, the Life-Cycle Assessment (LCA) methodology is used, and two water production plants are compared. The brackish groundwater scenario is based on a plant located in Almería (southern Spain), while the sea water scenario is based on literature data. Four impact categories and two environmental indicators, one of them related to brine discharge, are included. The results show that the key life-cycle issue of brackish groundwater desalination is electricity consumption, and since this is substantially reduced with regard to using sea water, the life-cycle impacts are found to be almost 50% lower. An uncertainty analysis based on Monte-Carlo simulation shows that these environmental savings are significant for all impact categories. Potential local impacts provoked by brine discharge are also found to be lower, due to a reduced content of salts. It is concluded that, when and wherever possible, exploitation of brackish groundwater resources should be assigned priority to sea water resources as an input for reverse osmosis desalination, although it must be taken into account that groundwater, as opposed to sea water, is a limited resource.     

我国反渗透海水淡化能量回收装置研究与应用现状

能量回收装置可以大幅降低反渗透海水淡化的产水能耗和制水成本,是反渗透海水淡化系统的标准配置。简述了水力透平式和功交换式能量回收装置的发展历程与其特点,综述了我国能量回收装置研究现状,比较了典型能量回收装置的性能,列举了2005年以来能量回收装置在我国万吨级以上反渗透海水淡化工程中的应用情况。功交换式能量回收装置的能量回收效率高达90%以上,已经成为海水淡化行业研究和应用的热点,其中国产功交换式能量回收装置已在国内大型反渗透海水淡化工程中开始应用。     

Quantitative biofouling diagnosis in full scale nanofiltration and reverse osmosis installations

Biofilm accumulation in nanofiltration and reverse osmosis membrane elements results in a relative increase of normalised pressure drop (ΔNPD). However, an increase in ΔNPD is not exclusively linked to biofouling. In order to quantify biofouling, the biomass parameters adenosine triphosphate (ATP), total cell count and heterotrophic plate count in membrane elements were investigated during membrane autopsies and compared with ΔNPD in test rigs and 15 full scale investigations with different types of feed water. The combination of biomass related parameters ATP and total cell count in membrane elements seem to be suitable parameters for diagnosis of biofouling, whereas plate counts were not appropriate to assess biofouling. The applied ΔNPD measurement was too insensitive for early detection of fouling. Measurements of biological parameters in the water were shown to be not appropriate in quantifying biofouling. Evidently, there is a need for a practical tool, sensitive pressure drop data and systematic research.     

双膜法在市政污水处理厂的应用

天津市某污水处理厂再生水回用工程采用双膜法工艺,近期设计规模为2.0×10^4m^3/d,本文介绍了其工艺流程、设备配置情况、工程设计参数等.运行结果表明,采用双膜法对废水进行处理后出水水质良好,可以达到回用标准,其中超滤出水浊度为0.01～0.04 NTU,反渗透产水电导率＜ 15 μs/cm,脱盐率大于99％.经济性分析结果显示,该双膜法再生水回用工程的吨水运行成本为1.584元,具有良好的经济及环境效益.     

膜技术进步及其对海水淡化的影响

介绍了反渗透膜技术的最新进展,分析了其对海水淡化的影响,提出了我国海水淡化事业发展应关注和解决的问题.     

Water purification of nitrates by low-pressure reverse osmosis method

The paper has investigated possibilities and basic regularities of water purification of nitrates by low pressure reverse osmosis. The negative influence of chlorides and sulfates on the process characteristic have bee shown. A conclusion has bee made on expediency of using the low pressure reverse osmosis method for purifying water of nitrates.