Forward osmosis (FO) has gained significant research interest due to the wide range of potential applications in desalination and wastewater reuse. However, the FO process being concentration (osmosis) driven has its own intrinsic limitations. Net transfer of water across the membrane occurs until the point of osmotic equilibrium between the draw solution (DS) and the feed solution (FS). Without external intervention, it is impossible to dilute the DS beyond the point of osmotic equilibrium. In this study, the concept of osmotic equilibrium in the FO process is introduced by simulating conditions in a plate-and-frame FO membrane module using established mass transport models. The simulations evaluated the influence of various operating parameters on process performance, assessed in terms of water flux, feed recovery rate and the final concentration of the diluted DS. The counter-current crossflow mode of operation has been observed to be advantageous because it can achieve higher module average water flux, higher feed water recovery rates and higher DS final dilution. Based on the osmotic equilibrium concept and mass balance analysis, a modified equation for the water extraction capacity of a draw solute has been proposed. This study underscores the need for process optimisation for large-scale FO operations. © 2013 Elsevier B.V.

Phuntsho Sherub    Seungkwan Hong    Menachem Elimelech     Shon Ho Kyong   

Journal of Membrane Science

2014

In this study, we systematically investigated the propensity and reversibility of combined organic-colloidal fouling in forward osmosis (FO) under various solution chemistries (pH and calcium ion concentrations) and applied hydraulic pressure on the feed side. Alginate, silica colloids, and their mixture (i.e., combined organic-colloidal) were used as model foulants. Our findings demonstrate that combined organic-colloidal foulants caused more rapid flux decline than the individual foulants due to the synergistic effect of alginate and silica colloids. As a result, much lower flux recovery was achieved by physical cleaning induced by increasing the cross-flow rate, in contrast to single foulants of which the fouling layer was easily removed under all solution conditions. Interestingly, less flux decline was observed at neutral pH for combined fouling, while acidic conditions were favorable for alginate fouling and basic solutions caused more silica fouling, thereby providing clear evidence for the combined fouling effect. It was also found that calcium ions enhanced water flux decline and induced the formation of less reversible combined organic-colloidal fouling layers. Lastly, the role of applied hydraulic pressure on the feed side in FO was examined to elucidate the mechanism of fouling layer formation, fouling reversibility, and water flux recovery. Higher fouling propensity and lower fouling reversibility of combined organic-colloidal fouling were observed in the presence of applied hydraulic pressure on the feed side. This observation suggests that the lower fouling propensity and greater fouling reversibility in FO compared to reverse osmosis (RO), are attributable to unpressurized operating conditions in FO. © 2014 Elsevier B.V.

Kim Yeowon    Menachem Elimelech     Shon Ho Kyong    Seungkwan Hong   

Journal of Membrane Science

2014

Providing students opportunities to appreciate interdisciplinary systems remains a challenge for educators at all levels. Sensing and data-logging in the environment and in engineered systems offer a unique opportunity for students to explore the connections between engineering processes, analog signals, and digital outputs. Here, we present the design of a device that uses an infrared sensor and microcontroller to measure and record low liquid flow rates. We designed this device using the open-source Arduino™ microcontroller platform, which can stand alone or interface with a PC to display data in real time. In order to demonstrate the usefulness of this device in the undergraduate learning laboratory, we have incorporated it into a membrane distillation system. Building and experimenting with such devices helps students practice and learn creativity, troubleshooting, and programming fundamentals, allowing them to understand the importance of electrical engineering and computer programming in the context of chemical and environmental engineering. © 2014 IEEE.

Katherine Zodrow    Coulter Valerie H.    Shaulsky Evyatar    Menachem Elimelech    

Proceedings of the 4th Interdisciplinary Engineering Design Education Conference, IEDEC 2014

2014

We report on the development of a liquid crystalline block copolymer with brush-type architecture as a platform for creating functional materials by magnetic-field-directed self-assembly. Ring-opening metathesis of n-alkyloxy cyanobiphenyl and polylactide (PLA) functionalized norbornene monomers provides efficient polymerization yielding low polydispersity block copolymers. The mesogenic species, spacer length, monomer functionality, brush-chain length, and overall molecular weight were chosen and optimized to produce hexagonally packed cylindrical PLA domains which self-assemble and align parallel to an applied magnetic field. The PLA domains can be selectively removed by hydrolytic degradation resulting in the production of nanoporous films. The polymers described here provide a versatile platform for scalable fabrication of aligned nanoporous materials and other functional materials based on such templates. © 2014 American Chemical Society.

Deshmukh Prashant    Manesh Gopinadhan    Youngwoo Choo    Ahn Suk-Kyun    Paweł Majewski    Yoon Sook Young    Bakajin Olgica    Menachem Elimelech     Chinedum Osuji    Rajeswari Kasi   

ACS Macro Letters

2014

Adequate fate descriptors are crucial input parameters in models used to predict the behaviour and transport of a contaminant in the environment and determine predicted environmental concentrations for risk assessment. When new fate models are being developed for emerging contaminants, such as engineered nanoparticles (ENPs), special care has to be applied in adjusting conventional approaches and fate descriptors to a new set of substances. The aim of this paper is to clarify misconceptions about the applicability of equilibrium partition coefficients, such as the octanol-water partition coefficient (Kow) or the soil-water distribution coefficient (Kd), whose application in the context of ENP fate assessment is frequently suggested despite lacking scientific justification. ENPs are present in the environment as thermodynamically unstable suspensions and their behaviour must be represented by kinetically controlled attachment and deposition processes as has been established by colloid science. Here, we illustrate the underlying theories of equilibrium partitioning and kinetically controlled attachment and discuss why the use of any coefficient based on equilibrium partitioning is inadequate for ENPs and can lead to significant errors in ENP fate predictions and risk assessment.

Antonia Praetorius    Nathalie Tufenkji    Kai uwe Goss    Martin Scheringer    Frank Von Der Kammer    Menachem Elimelech    

Environmental Science: Nano

2014

We investigate the performance of pressure retarded osmosis (PRO) at the module scale, accounting for the detrimental effects of reverse salt flux, internal concentration polarization, and external concentration polarization. Our analysis offers insights on optimization of three critical operation and design parameters - applied hydraulic pressure, initial feed flow rate fraction, and membrane area - to maximize the specific energy and power density extractable in the system. For co- and counter-current flow modules, we determine that appropriate selection of the membrane area is critical to obtain a high specific energy. Furthermore, we find that the optimal operating conditions in a realistic module can be reasonably approximated using established optima for an ideal system (i.e., an applied hydraulic pressure equal to approximately half the osmotic pressure difference and an initial feed flow rate fraction that provides equal amounts of feed and draw solutions). For a system in counter-current operation with a river water (0.015 M NaCl) and seawater (0.6 M NaCl) solution pairing, the maximum specific energy obtainable using performance properties of commercially available membranes was determined to be 0.147 kWh per m³ of total mixed solution, which is 57% of the Gibbs free energy of mixing. Operating to obtain a high specific energy, however, results in very low power densities (less than 2 W/m²), indicating that the trade-off between power density and specific energy is an inherent challenge to full-scale PRO systems. Finally, we quantify additional losses and energetic costs in the PRO system, which further reduce the net specific energy and indicate serious challenges in extracting net energy in PRO with river water and seawater solution pairings.

Anthony Straub    Shihong Lin    Menachem Elimelech    

Environmental Science and Technology

2014

Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4⁺) and sodium (Na⁺) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes.

Xinglin Lu    Chanhee Boo    马军    Menachem Elimelech    

Environmental Science and Technology

2014

We have demonstrated the application of osmotic back-flushing (OBF) for the removal of biofilms from reverse osmosis (RO) membranes and proposed a new biofilm dispersal mechanism. OBF was conducted in a laboratory-scale RO test cell by introducing a sequence of hypersaline solution (1.5 M NaCl) flushes into the feedwater, while still maintaining the applied hydraulic pressure (13.8 bar). OBF resulted in significant biofilm detachment, leaving a thin, perforated bacterial film (24 μm thickness) with vertical cavities ranging from 15 to 50 μm in diameter. Application of OBF led to significant reductionin the biovolume (70-79%) and substantial removal of total organic carbon and proteins (78 and 66%, respectively), resulting in 63% permeate water flux recovery. Our findings demonstrate the potential of this chemical-free RO membrane cleaning method while highlighting the possible challenges of the technique.

Edo Bar-Zeev    Menachem Elimelech    

Environmental Science and Technology Letters

2014

In the rapidly developing shale gas industry, managing produced water is a major challenge for maintaining the profitability of shale gas extraction while protecting public health and the environment. We review the current state of practice for produced water management across the United States and discuss the interrelated regulatory, infrastructure, and economic drivers for produced water reuse. Within this framework, we examine the Marcellus shale play, a region in the eastern United States where produced water is currently reused without desalination. In the Marcellus region, and in other shale plays worldwide with similar constraints, contraction of current reuse opportunities within the shale gas industry and growing restrictions on produced water disposal will provide strong incentives for produced water desalination for reuse outside the industry. The most challenging scenarios for the selection of desalination for reuse over other management strategies will be those involving high-salinity produced water, which must be desalinated with thermal separation processes. We explore desalination technologies for treatment of high-salinity shale gas produced water, and we critically review mechanical vapor compression (MVC), membrane distillation (MD), and forward osmosis (FO) as the technologies best suited for desalination of high-salinity produced water for reuse outside the shale gas industry. The advantages and challenges of applying MVC, MD, and FO technologies to produced water desalination are discussed, and directions for future research and development are identified. We find that desalination for reuse of produced water is technically feasible and can be economically relevant. However, because produced water management is primarily an economic decision, expanding desalination for reuse is dependent on process and material improvements to reduce capital and operating costs. © 2013 American Chemical Society.

Devin Shaffer    Hoover Laura A.    Moshe Ben-Sasson    Santiago Romero-Vargas Castrillón    Ngai yin Yip    Menachem Elimelech    

Environmental Science and Technology

2013

This study demonstrates the robustness and treatment capacity of a forward osmosis (FO)-membrane distillation (MD) hybrid system for small-scale decentralized sewer mining. A stable water flux was realized using a laboratory-scale FO-MD hybrid system operating continuously with raw sewage as the feed at water recovery up to 80%. The hybrid system also showed an excellent capacity for the removal of trace organic contaminants (TrOCs), with removal rates ranging from 91 to 98%. The results suggest that TrOC transport through the FO membrane is governed by "solute-membrane" interaction, whereas that through the MD membrane is strongly correlated to TrOC volatility. Concentrations of organic matter and TrOCs in the draw solution increased substantially as the water recovery increased. This accumulation of some contaminants in the draw solution is attributed to the difference in their rejection by the FO and MD systems. We demonstrate that granular activated carbon adsorption or ultraviolet oxidation could be used to prevent contaminant accumulation in the draw solution, resulting in near complete rejection (>99.5%) of TrOCs. © 2013 American Chemical Society.

Ming Xie    Nghiem L.    William Price    Menachem Elimelech    

Environmental Science and Technology

2013