One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

Runnan Zhang    Yanan Liu    He Mingrui    Yanlei Su    Xueting Zhao    Menachem Elimelech     姜忠义   

Chemical Society Reviews

2016

A biocidal coating was developed in order to reduce biofouling on a reverse osmosis (RO) membrane using a quaternary ammonium (QA) functionalized polymer. The synthesis of a series of polysulfone (PS) ionomers with QA groups is described, and a method for spraying these QA ionomers as an alcoholic solution, which dried into water insoluble coatings. Contact angle and streaming potential were used to analyze the coating's hydrophilicity and surface charge. Both PS-QA1 and the commercial RO membrane had an apparent contact angle of 68° that increased to 126° for PS-QA12 corresponding to alkyl chain length. A negatively charged particle-probe was used to measure coated and uncoated RO membrane interaction forces. Measured interaction forces correlated strongly with the length of alkyl chains or hydrophobicity of the coated surfaces. Uncoated RO membranes and ones coated with PS-QA were exposed to suspensions of Escherichia coli cells. All four PS-QA coatings showed significant biotoxicity and killed 100% of the E. coli cells, but uncoated RO membranes had metabolically active biofilms. However, coatings tested in a RO crossflow system showed a flux reduction that is attributed to mass transfer resistance due to excessively thick films.

Michael Hibbs    McGrath Lucas K.    Kang Seoktae    Adout Atar    Altman Susan J.    Menachem Elimelech     Cornelius Chris J.   

Desalination

2016

The enormous potential of harvesting energy from salinity gradients has been discussed for decades, and pressure-retarded osmosis (PRO) is being increasingly investigated as a method to extract this energy. Despite advancements in membranes and system components, questions still remain regarding the overall viability of the PRO process. Here, we review PRO focusing on the net energy extractable and the ultimate feasibility of the most widely explored configurations. We define the maximum energy that can be obtained from the process, quantify losses and energetic costs that will reduce the net extractable energy, and explain how membrane modules can be improved. We then explore the potential of three configurations of PRO: systems designed to control mixing where rivers meet the sea, power plants that utilize the high concentration gradients available from hypersaline solutions, and PRO systems incorporated into reverse osmosis desalination plants to reduce electricity requirements. We conclude by considering the overall outlook of the process and identifying the most pressing challenges for future research.

Anthony Straub    Deshmukh Akshay    Menachem Elimelech    

Energy and Environmental Science

2016

Zero liquid discharge (ZLD) - a wastewater management strategy that eliminates liquid waste and maximizes water usage efficiency - has attracted renewed interest worldwide in recent years. Although implementation of ZLD reduces water pollution and augments water supply, the technology is constrained by high cost and intensive energy consumption. In this critical review, we discuss the drivers, incentives, technologies, and environmental impacts of ZLD. Within this framework, the global applications of ZLD in the United States and emerging economies such as China and India are examined. We highlight the evolution of ZLD from thermal- to membrane-based processes, and analyze the advantages and limitations of existing and emerging ZLD technologies. The potential environmental impacts of ZLD, notably greenhouse gas emission and generation of solid waste, are discussed and the prospects of ZLD technologies and research needs are highlighted.

Tiezheng Tong    Menachem Elimelech    

Environmental Science and Technology

2016

In this study, we analyze the effects of membrane properties, namely water permeability, solute permeability, and structural parameter, on the overall performance of an FO membrane module to extract water from simulated seawater (0.6M NaCl). By considering the thermodynamic limit of operation, we demonstrate that the maximum achievable water recovery is practically independent of membrane properties, and higher maximum water recovery is achievable with counter-current compared to co-current mode. Analysis of the module-scale model indicates that reducing the support layer structural parameter offers substantial reductions in the membrane area required to achieve a specified water recovery. For example, a 25% reduction of the structural parameter of a state-of-the-art thin-film composite (TFC) membrane (from 400 to 300μm) yields a sizable 20% reduction in membrane area. In contrast, quintupling the water permeability coefficient (from 2.0 to 10.0Lm^-2h^-1bar^-1) of a modern TFC membrane generates only a modest 10% saving in membrane area. In addition, because of the permeability-selectivity trade-off that governs current polymeric membranes, doubling the water permeability coefficient would cause crippling ~7-fold increases in forward and reverse solute permeation. This quantitative study models the potential performance of a module-scale FO desalination process and firmly highlights the need to prioritize the reduction of support layer mass transport resistances over water permeability increases in membrane development.

Deshmukh Akshay    Ngai yin Yip    Shihong Lin    Menachem Elimelech    

Journal of Membrane Science

2015

A novel osmotic dilution process using commercial liquid fertilizer for greenwall irrigation was evaluated. In this process, clean water was extracted from raw sewage by forward osmosis (FO) using a well-balanced, all-purpose commercial liquid fertilizer as draw solution. The diluted liquid fertilizer can then be used for direct sustainable greenwall irrigation. Our results show that the presence of organic matter in the liquid fertilizer draw solution did not compromise FO membrane performance. No discernible changes in water flux and key membrane transport parameters (pure water permeability coefficient, A, and salt (NaCl) permeability coefficient, B) were observed when the organic matter concentration in the draw solution was increased to 2000. mg/L. Parameters influencing the osmotic dilution process were examined in terms of reverse salt flux, liquid fertilizer concentration, cross-flow rate, and feed and liquid fertilizer draw solution temperatures. The reverse flux of phosphate was much lower compared to those of ammonium and potassium as the reverse flux of these solutes were proportionally related to their hydrated radii. Cross-flow rate had no discernible impact on either water flux or reverse nutrient transport. Water and reverse nutrient fluxes increased markedly with increasing temperature, driven by higher water and solute diffusivities. More than 80% water recovery was achieved by osmotic dilution using raw sewage feed. Water production was stable and not affected by deposition of organic matter on the membrane surface. By contrast, reverse nutrient diffusion was hindered due to enhanced steric hindrance. Results reported here have significant environmental implications. Extracting clean water from raw sewage by commercial liquid fertilizers harnesses unique FO mass transfer phenomena and balances greenwall nutrient requirement, thereby sustaining the greenwall irrigation process.

Ming Xie    Zheng Mingxin    Paul Cooper    William Price    Nghiem L.    Menachem Elimelech    

Journal of Membrane Science

2015

Forward osmosis (FO) has been extensively investigated in the past decade. Despite significant advancements in our understanding of the FO process, questions and challenges remain regarding the energy efficiency and current state of the technology. Here, we critically review several key aspects of the FO process, focusing on energy efficiency, membrane properties, draw solutes, fouling reversibility, and effective applications of this emerging technology. We analyze the energy efficiency of the process, disprove the common misguided notion that FO is a low energy process, and highlight the potential use of low-cost energy sources. We address the key necessary membrane properties for FO, stressing the importance of the structural parameter, reverse solute flux selectivity, and the constraints imposed by the permeability-selectivity tradeoff. We then dispel the notion that draw solution regeneration can use negligible energy, highlighting the beneficial qualities of small inorganic and thermolytic salts as draw solutes. We further discuss the fouling propensity of FO, emphasizing the fouling reversibility of FO compared to reverse osmosis (RO) and the prospects of FO in treating high fouling potential feed waters. Lastly, we discuss applications where FO outperforms other desalination technologies and emphasize that the FO process is not intended to replace RO, but rather is to be used to process feed waters that cannot be treated by RO.

Devin Shaffer    Werber Jay R.    Jaramillo Humberto    Shihong Lin    Menachem Elimelech    

Desalination

2015

Transparent exopolymer particles (TEP) are ubiquitous in marine and freshwater environments. For the past two decades, the distribution and ecological roles of these polysaccharide microgels in aquatic systems were extensively investigated. More recent studies have implicated TEP as an active agent in biofilm formation and membrane fouling. Since biofouling is one of the main hurdles for efficient operation of membrane-based technologies, there is a heightened interest in understanding the role of TEP in engineered water systems. In this review, we describe relevant TEP terminologies while critically discussing TEP biological origin, biochemical and physical characteristics, and occurrence and distributions in aquatic systems. Moreover, we examine the contribution of TEP to biofouling of various membrane technologies used in the desalination and water/wastewater treatment industry. Emphasis is given to the link between TEP physicochemical and biological properties and the underlying biofouling mechanisms. We highlight that thorough understanding of TEP dynamics in feedwater sources, pretreatment challenges, and biofouling mechanisms will lead to better management of fouling/biofouling in membrane technologies. (Figure Presented).

Edo Bar-Zeev    Passow Uta    Santiago Romero-Vargas Castrillón    Menachem Elimelech    

Environmental Science and Technology

2015

Graphene oxide (GO) is a promising material for the development of antimicrobial surfaces due to its contact-based antimicrobial activity. However, the relationship between GO physicochemical properties and its antimicrobial activity has yet to be elucidated. In this study, we investigated the size-dependency of GO antimicrobial activity using the Gram-negative bacteria Escherichia coli. GO suspensions of average sheet area ranging from 0.01 to 0.65 μm² were produced and their antimicrobial activity evaluated in cell suspensions or as a model GO surface coating. The antimicrobial activity of GO surface coatings increased 4-fold when GO sheet area decreased from 0.65 to 0.01 μm². The higher antimicrobial effect of smaller GO sheets is attributed to oxidative mechanisms associated with the higher defect density of smaller sheets. In contrast, in suspension assays, GO interacted with bacteria in a cell entrapment mechanism; in this case, the antimicrobial effect of GO increased with increasing sheet area, with apparent complete inactivation observed for the 0.65 μm² sheets after a 3 h exposure. However, cell inactivation by GO entrapment was reversible and all initially viable cells could be recovered when separated from GO sheets by sonication. These findings provide useful guidelines for future development of graphene-based antimicrobial surface coatings, where smaller sheet sizes can increase the antimicrobial activity of the material. Our study further emphasizes the importance of an accurate assessment of the antimicrobial effect of nanomaterials when used for antimicrobial surface design.

François Perreault    Andréia fonseca De    Siamak Nejati    Menachem Elimelech    

ACS Nano

2015

We have investigated biofouling behavior in forward osmosis (FO) and reverse osmosis (RO) membrane systems. Analysis of these two systems was done via comparison of biofilm structure and membrane permeate water flux decline. Experiments were performed using a model wastewater solution inoculated with Pseudomonas aeruginosa in laboratory-scale FO and RO test cells. For a meaningful comparison, biofouling runs were carried out using the same thin-film composite polyamide FO membrane, identical hydrodynamic conditions, and an initial permeate water flux of 19Lm^-2h^-1. Water flux decline after 600mL of cumulative permeate volume (or ~17-18h of fouling) was significantly lower in FO (~10%) compared to RO (~30%). FO biofilms grew in a loosely organized thick layer, with eminent mushroom-shaped structures, while RO biofilms grew in tightly organized mats encased in larger amounts of extracellular polymeric substances (EPS) per cell. The more compact biofilms in RO induced greater biofilm-enhanced osmotic pressure and hydraulic resistance to water flow compared to FO, which resulted in higher flux decline. We attribute the differences in biofouling behaviors in FO and RO to the different driving forces: osmotic pressure in FO and hydraulic pressure in RO.

Kwan Sarah E.    Edo Bar-Zeev    Menachem Elimelech    

Journal of Membrane Science

2015