Fouling and long-term durability of an integrated forward osmosis and membrane distillation system

Forward Osmosis Membrane: Review of Fabrication, Modification, Challenges and Potential

Forward osmosis (FO) is a low-energy treatment process driven by osmosis to induce the separation of water from dissolved solutes/foulants through the membrane in hydraulic pressure absence while retaining all of these materials on the other side. All these advantages make it an alternative process to reduce the disadvantages of traditional desalination processes. However, several critical fundamentals still require more attention for understanding them, most notably the synthesis of novel membranes that offer a support layer with high flux and an active layer with high water permeability and solute rejection from both solutions at the same time, and a novel draw solution which provides low solute flux, high water flux, and easy regeneration. This work reviews the fundamentals controlling the FO process performance such as the role of the active layer and substrate and advances in the modification of FO membranes utilizing nanomaterials. Then, other aspects that affect the performance of FO are further summarized, including types of draw solutions and the role of operating conditions. Finally, challenges associated with the FO process, such as concentration polarization (CP), membrane fouling, and reverse solute diffusion (RSD) were analyzed by defining their causes and how to mitigate them. Moreover, factors affecting the energy consumption of the FO system were discussed and compared with reverse osmosis (RO). This review will provide in-depth details about FO technology, the issues it faces, and potential solutions to those issues to help the scientific researcher facilitate a full understanding of FO technology.

Fouling and wetting in the membrane distillation driven wastewater reclamation process - A review

Fouling and wetting of membranes are significant concerns that can impede the widespread application of the membrane distillation (MD) process during high-salinity wastewater reclamation. Fouling, caused by the accumulation of undesirable materials on the membrane surface and pores, causes a decrease in permeate flux. Membrane wetting, the direct permeation of the feed solution through the membrane pores, results in reduced contaminant rejection and overall process failure. Lately, the application of MD for water recovery from various types of wastewaters has gained increased attention among researchers. In this review, we discuss fouling and wetting phenomena observed during the MD process, along with the effects of various mitigation strategies. In addition, we examine the interactions between contaminants and different types of MD membranes and the influence of different operating conditions on the occurrence of fouling and wetting. We also report on previously investigated feed pre-treatment options before MD, application of integrated MD processes, the performance of fabricated/modified MD membranes, and strategies for MD membrane maintenance during water reclamation. Energy consumption and economic aspects of MD for wastewater recovery is also discussed. Throughout the review, we engage in dialogues highlighting research needs for furthering the development of MD: the incorporation of MD in the overall wastewater treatment and recovery scheme (including selection of appropriate membrane material, suitable pre-treatment or integrated processes, and membrane maintenance strategies) and the application of MD in long-term pilot-scale studies using real wastewater.

Osmotically and Thermally Isolated Forward Osmosis-Membrane Distillation (FO-MD) Integrated Module

In this study, we propose a novel module design to integrate forward osmosis (FO) and membrane distillation (MD). The two processes are sealed in one module and operated simultaneously, making the system compact and suitable for a wide range of applications. To evaluate the system under large-scale module operating conditions, FO and MD experiments were performed separately. The effect of draw solution (DS) temperature on the FO performance was first assessed in terms of flux, reverse salt flux (RSF), and specific RSF (SRSF). While a higher DS temperature resulted in an increased RSF, a higher FO flux was achieved, with a lower SRSF. The influence of DS concentration on the MD performance was then investigated in terms of flux and salt rejection. High DS concentration had a slightly negative impact on MD water vapor flux, but the MD membrane was a complete barrier for DS salts. The FO-MD integrated module was simulated based on mass balance equations. Results indicated that initial DS (MD feed) flow rate and concentration are the most important factors for stable operation of the integrated module. Higher initial DS flow rate and lower initial DS concentration can achieve a higher permeate rate of the FO-MD module.

FO/MD hybrid system for real dairy wastewater recycling

This study investigated a forward osmosis and membrane distillation (FO/MD) hybrid system for real dairy wastewater (DWW) recycling. Two types of FO membranes, cellulose triacetate-embedded polyester screen support (CTA-ES) and aquaporin inside (AQP), were employed. Sodium chloride was used as the draw solution. A cross-flow FO cell and an air gap membrane distillation module were established to conduct individual FO experiments and FO/MD experiments. From the experiments, an analysis of the water flux (J_w), reverse draw solute flux (J_s), J_s/J_w ratio and contaminant rejection was performed. The reverse draw solute flux was determined by monitoring the chlorine ions in the feed solution of the FO process. The study demonstrated that real DWW could be reclaimed by the FO/MD hybrid system for the reuse of urban recycled water or for higher grade utilization. The DWW flux was influenced by feed foulants, the fouling stage as well as membrane properties. Furthermore, the J_s/J_w ratios were lower and more invariable for the CTA-ES membrane than for the AQP membrane, suggesting that the CTA-ES membrane had superior filtration performance. A fouled CTA-ES membrane could recover 90% of the flux after membrane cleaning.

Performance evaluation of hybrid OMBR-MD using organic and inorganic draw solutions

The performance of two inorganic divalent salts (CaCl_2, and MgCl₂) and two organic salts (CH₃COONa and Mg(CH₃COO)₂) was compared with commonly used NaCl in an osmotic membrane bioreactor (OMBR) integrated with a membrane distillation (MD) system. The system was investigated in terms of salinity buildup, flux stability, draw solution (DS) recovery and contaminants removal efficiency. Results indicated that organic DSs not only lessen the salt accumulation within the bioreactor but also increase the pollutant removal efficiency by improving biological treatment. Of all the draw solutions, NaCl and CaCl₂ produced rapid declines in water flux because of the high salt accumulation in the bio-tank as compared to other salts. The DCMD system successfully recovered all organic and inorganic draw solute concentrations as per OMBR requirements. Membrane flushing frequency for the MD system followed the order Mg(CH₃COO)₂ > CH₃COONa > CaCl₂ > MgCl₂ > NaCl. More than 90% removal of chemical oxygen demand (COD), NH₄ ⁺-N, and PO₄ ^3--P was achieved in the permeate for each salt because of the dual barriers of high-retention membranes i.e., forward osmosis and MD.