Feasibility of membrane processes for the recovery and purification of bio-based volatile fatty acids: A comprehensive review

Volatile fatty acids (VFAs) can be produced from fermentation/anaerobic digestion of wastes and are a valuable substrate for numerous applications, such as those related to the food, tanning, petrochemicals, pharmaceuticals, cosmetics, and chemicals industry. They are also inexpensive raw materials for developing alternative sources of energy. However, the separation and purification of VFAs produced from fermented wastewaters are not straightforward goals, due to the low concentration of these compounds in the fermentation broths and owing to the complexity of these mixtures. Cost-effective and sustainable technologies must be developed to recover VFAs efficiently and allow their beneficial use. In this paper, a comprehensive review of VFAs recovery/purification methods is provided, with focus on membrane-based processes. First, the VFAs production methods, application, and conventional processes (distillation, precipitation, adsorption, and extraction) for their recovery are briefly reviewed. Then, the ability of various membrane-based techniques to separate and purify VFAs are evaluated and discussed in detail. This discussion includes the processes of microfiltration/ultrafiltration, nanofiltration, reverse osmosis, forward osmosis, membrane distillation, electrodialysis, membrane contractor, and pervapo- ration. Extensive background and examples of applications are also provided to show the effectiveness of membrane processes. Finally, challenges and future research directions are highlighted

Loose nanofiltration membranes functionalized with in situ-synthesized metal organic framework for water treatment

In this study, modified loose nanofiltration membranes were prepared by in-situ decoration with Zeolitic Imidazolate Framework-7 (ZIF-7) on the surface of porous polyethersulfone substrates functionalized with co-deposited sulfobetaine methacrylate (SBMA) zwitterion (ZW) and polydopamine (PDA). With the aid of ZW/PDA active layer co-deposition under mild conditions, ZIF-7 metal organic framework (MOF) nanocrystals were successfully formed and anchored onto the membrane surface via both non-covalent and covalent bonds to simultaneously achieve the desired selectivity and productivity of the loose nanofiltration membranes. The characterization results confirmed the successful deposition of the ZW/PDA active layer and the consequent decoration with ZIF-7 nanocrystals. The average water contact angle decreased notably from 81.4 to 51.43 degrees upon the formation of ZIF-7. This membrane showed high rejection (~99.9%) of methyl blue and Congo red dyes and high water flux with dye solutions (around 40 L m-2h-1) at a very low applied pressure of 1.5 bar. Moreover, the filtration experiments revealed that functionalized membranes exhibited a significant reduction in fouling and biofouling propensity. Notably, the MOF-SBMA/PDA membrane displayed favorable antifouling behavior associated with a significant ability to recover flux upon simple physical cleaning. The combination of these two properties is possibly the most promising feature of the membrane proposed in this study

Functionalized polyamide membranes yield suppression of biofilm and planktonic bacteria while retaining flux and selectivity

Biofouling is a major challenge for desalination, water treatment, and water reuse applications using polymer-based membranes. Two classes of novel silver-based metal azolate frameworks (MAF) are proposed to decorate polyamide (PA) forward osmosis membranes and to improve numerous aspects of fouling and transport. Membranes functionalized with two concentrations of each MAF are compared with a pristine control material, with results that clearly highlight their tunability and bio-inhibitory effects. We report for the first time PA membranes yielding near complete suppression of a robust biofilm-forming bacterium (Pseudomonas aeruginosa) and inactivation of planktonic bacteria, while maintaining high selectivity. These features improve the long-term water flux performance of the membranes, tested during 24 h of accelerated biofouling and organic fouling conditions, and showing lower than 10% and 20% decline in water flux. These enhancements were achieved with only 0.03–0.06% mass of additives and little generation of hazardous waste products, indicating that low-cost and environmentally benign functionalization can prevent biofouling growth while maintaining selectivity and transport for high-performance desalination, water treatment and reuse

Recent advances in functionalized polymer membranes for biofouling control and mitigation in forward osmosis

Forward osmosis (FO) is an osmotically driven process widely studied for water desalination, wastewater treatment, and water reuse, as well as dilution and concentration of aqueous streams. However, its application is still hampered by the lack of ideal draw solutes, high-performance membranes, and fouling/biofouling. Biofouling is particularly challenging when FO is applied for seawater desalination and wastewater treatment. Over the last decade, many attempts have been made to exploit advances in materials science to obtain membranes with anti-biofouling properties to prevent or to reduce the detrimental effects of this phenomenon. In this review, we address the various approaches of membrane surface functionalization for biofouling control and mitigation. Recent developments in surface modification of thin-film composite and asymmetric membranes using surface coating, surface functionalization, and incorporation of tailored materials for biofouling control in FO are critically discussed. The future perspectives of anti-biofouling materials and FO membranes are reviewed to shed light on the future research directions for developing the true potential surface modification approach for the FO process

Improved antifouling and antibacterial properties of forward osmosis membranes through surface modification with zwitterions and silver-based metal organic frameworks

This study investigates the effect of surface functionalization of a thin-film composite forward osmosis membrane with zwitterions and silver-based metal organic frameworks (Ag-MOFs) to improve the antifouling, anti-biofouling, and antimicrobial activity of the membrane. Two types of zwitterions, namely, 3-bromopropionic acid and 1,3-propane sultone, are chemically bonded, with and without incorporation of Ag-MOFs, over the surface of a polyamide membrane. Spectroscopy measurements indicate successful grafting of the modifying agents on the membrane surface. Contact angle measurements demonstrate a notable improvement in surface wettability upon functionalization. The performance of the membranes is evaluated in terms of water and salt fluxes in forward osmosis filtrations. The transport data show demonstrably increased water flux of around 300% compared to pristine membranes, with similar or slightly reduced salt reverse flux. The antifouling and anti-biofouling properties of the modified membranes are evaluated using sodium alginate and E. coli, respectively. These experiments reveal that functionalized membranes exhibit significant antifouling and anti-biofouling behavior, with high resilience against flux decline