Membrane fouling in osmotically driven membrane processes: A review

Comparing membrane and spacer biofouling by Gram-negative Pseudomonas aeruginosa and Gram-positive Anoxybacillus sp. in forward osmosis

Bacteria of different Gram-types have inherently different outer cell structures, influencing cell surface properties and bacterial attachment. Dynamic biofouling experiments were conducted over four days in a bench-scale forward osmosis (FO) system with Gram-negative Pseudomonas aeruginosa or Gram-positive Anoxybacillus sp. Biofouling resulted in ∼10% decline in FO permeate water flux and was found to be significant for Anoxybacillus sp. but not for P. aeruginosa. Additionally, a stronger permeate water flux decline for P. aeruginosa in experiments with a superhydrophilic feed spacer demonstrated that mitigation methods require testing with different bacterial Gram-types. It was found that although permeate water flux decline can be affected by bacterial Gram-type the stable performance under enhanced biofouling conditions highlights the potential of FO for wastewater reclamation.

Decontamination of radioactive wastewater: State of the art and challenges forward

Radioactive substances have been widely used in many industrial sectors, e.g. nuclear power station, biomedical engineering, etc. With increasing applications of nuclear technology, more and more radioactive wastewater is being generated via different channels, which indeed is posing an emerging challenge and threat to the environment and human health. Given such a situation, this review attempts to offer a holistic view with regard to the state of the art of technology for decontamination of radioactive wastewater as well as shed lights on the challenges forward. Different from reclamation of other types of wastewaters, the most challenging issue in decontamination of radioactive wastewater is the effective stabilization and solidification of soluble radioactive nuclides present in wastewater, which are critical for final disposal. Moreover, the potential risk of human exposure to wastewater radiation needs to be carefully assessed, and this issue should also be taken into consideration in the selection, design and operation of the radioactive wastewater treatment process. These clearly differentiate the treatment principle of radioactive wastewater from those of traditional industrial and municipal wastewaters. Lastly, the challenges from the perspectives of technology development, environmental and human health impacts and possible solutions forward are also elucidated.

Comparison of performance and biofouling resistance of thin-film composite forward osmosis membranes with substrate/active layer modified by graphene oxide

In this study, the influence mechanisms of graphene oxide (GO) on the membrane substrate/active layer for improving the water flux and anti-biofouling ability of thin-film composite (TFC) membranes in forward osmosis (FO) were systematically investigated. We fabricated a pristine TFC membrane, a TFC membrane in which the substrate or polyamide active layer was modified by GO (TFN-S membrane or TFN-A membrane), and a TFC membrane in which both the substrate and active layer were functionalized by GO (TFN-S + A membrane). Our results showed that the TFN-S membrane possesses a higher water flux (∼27.2%) than the TFN-A because the substrate that contained GO could improve the porous structure and porosity, while the TFN-A membrane exhibited a lower reverse salt flux and higher salt rejection than the TFN-S membrane, indicating that the surface properties played a more important role than the substrate for the salt rejection. Regarding the biofouling experiment, the TFN-A and TFN-S + A membranes facilitated a higher antifouling performance than the TFN-S and TFC membranes after 72 h of operation because of the greater hydrophilicity, lower roughness and facilitated higher bactericidal activity on the GO-modified surface. In addition, the biovolume and biofilm thickness of the TFN-A and TFN-S + A membranes were found to follow the same trend as flux decline performance. In conclusion, the substrate modified by GO could greatly improve the water flux, whereas the GO-functionalized active layer is favorable for salt rejection and biofouling mitigation. The advantage of TFN-A in biofouling mitigation suggests that the antibacterial effect of GO has a stronger influence on biofouling control than the changes of hydrophilicity and roughness.

The substrate modified by GO could greatly improve water flux, whereas the GO-functionalized active layer is favorable for biofouling mitigation.

Selection of performance reference compound (PRC) for passive sampling of pharmaceutical residues in an effluent dominated river

A passive sampling device, a polar organic chemical integrative sampler (POCIS), was used to monitor 13 pharmaceuticals and 8 transformation products in upstream and downstream wastewater treatment plant effluent. A POCIS laboratory calibration study was performed to determine uptake behavior and the effect of water flow on the sampling rate. Most compounds showed a linear accumulation, and the sampling rate values ranged from 0.031 to 0.559 L/day. The developed POCIS samplers were used in field experiments in a wastewater-impacted river. Using the calculated sampling rates, the time-weighted average concentration values were measured by three different approaches: (1) laboratory calibration sampling rates (2) performance reference compound (PRC) correction sampling rates and (3) field calibration sampling rates. Nine deuterated compounds (acetaminophen-d₃, antipyrine-d₃, sulfamethoxazole-d₄, carbamazepine-d₁₀, diclofenac acid-d₄, clofibric acid-d₄, bezafibrate-d₆, ibuprofen-d₃ and naproxen-d₃) were studied as PRCs. Antipyrine-d₃ was successfully tested as a PRC for sulfamethoxazole, ibuprofen, 2-hydroxy ibuprofen, diclofenac acid, 4-hydroxydiclofenac acid, carbamazepin, carbamazepin 10,11-epoxide, sulfadiazine, 1-naphthol, antipyrine, naproxen and 4-chlorobenzoic acid. Finally, the POCIS was used to monitor target compounds in river water and measure their attenuation. For most compounds, the POCIS attenuation results were not significantly different from those of the spot samples, which demonstrated that a POCIS with a PRC correction can determine the attenuation of organic micropollutants in rivers.

Thin Film Composite Membrane for Oily Waste Water Treatment: Recent Advances and Challenges

Oily wastewater discharge from various industry processes and activities have caused dramatic impacts on the human and environment. Treatment of oily wastewater using membrane technology has gained worldwide attention due to its efficiency in removing the amount and concentration of oil and grease as well as other specific pollutants in order to be reused or to fulfill stringent discharge standard. The application of thin film composite (TFC) membrane in reverse osmosis (RO) and forward osmosis (FO) for oily wastewater treatment is an emerging and exciting alternative in this field. This review presents the recent and distinctive development of TFC membranes to address the issues related to oily wastewater treatment. The recent advances in terms of TFC membrane design and separation performance evaluation are reviewed. This article aims to provide useful information and strategies, in both scientific knowledge advancement and practical implementation point of view, for the application TFC membrane for oily wastewater treatment.

Improved Anti-Biofouling Performance of Thin -Film Composite Forward-Osmosis Membranes Containing Passive and Active Moieties

Forward osmosis (FO) has gained increasing attention in desalination, wastewater treatment, and power generation. However, biofouling remains a major obstacle for the sustainable development of the FO process. Both passive and active strategies have been developed to mitigate membrane biofouling. A comprehensive understanding of different strategies and mechanisms has fundamental significance for the antifouling membrane development. In this study, thin-film composite (TFC) FO membranes were modified with polydopamine (PDA) coating as a passive antibacterial moiety and silver nanoparticles (Ag NPs) as an active antibacterial moiety. Their anti-biofouling performances were investigated both in static and dynamic conditions. In static exposure, the PDA-coated membranes exhibited great passive anti-adhesive property, and the Ag-NP-generated membranes presented both of excellent passive anti-adhesive properties and active antibacterial performance. While in dynamic cross-flow running conditions, Ag NPs effectively mitigated the membrane water flux decline due to their inhibition of biofilm growth, the PDA coating failed because of its inability to inactivate the attached bacteria growth. Moreover, Ag NPs were stable and active on membrane surfaces after 24 h of cross-flow operation. These findings provide new insights into the performances and mechanisms of passive and active moieties in the FO process.

Submerged Osmotic Processes: Design and Operation to Mitigate Mass Transfer Limitations

Submerged forward osmosis (FO) is of high interest for bioreactors, such as osmotic membrane bioreactor, microalgae photobioreactor, food or bioproduct concentration where pumping through pressurized modules is a limitation due to viscosity or breakage of fragile components. However, so far, most FO efforts have been put towards cross flow configurations. This study provides, for the first time, insights on mass transfer limitations in the operation of submerged osmotic systems and offer recommendations for optimized design and operation. It is demonstrated that operation of the submerged plate and frame FO module requires draw circulation in the vacuum mode (vacuum assisted osmosis) that is in favor of the permeation flux. However, high pressure drops and dead zones occurring in classical U-shape FO draw channel strongly disadvantage this design; straight channel design proves to be more effective. External concentration polarization (ECP) is also a crucial element in the submerged FO process since mixing of the feed solution is not as optimized as in the cross flow module unless applying intense stirring. Among the mitigation techniques tested, air scouring proves to be more efficient than feed solution circulation. However, ECP mitigation methodology has to be adapted to application specificities with regards to combined/synergetic effects with fouling mitigation.

Dopamine Incorporated Forward Osmosis Membranes with High Structural Stability and Chlorine Resistance

The degradation and detachment of the polyamide (PA) layer for the conventional thin-film composite (TFC) membranes due to chemical disinfectants cleaning with chlorine and material difference of PA layer and substrate are two major bottlenecks of forward osmosis (FO) technology. In this study, a new type of FO membranes was first prepared by controlling dopamine (DA) as the sole amine in the aqueous phase and the reaction with trimesoyl chloride (TMC) as the acyl chloride during interfacial polymerization (IP) process. The influence of membrane synthesis parameters such as monomer concentration, pH of the aqueous phase, IP reaction time and IP temperature were systematically investigated. The optimized membrane showed both improved structure stability and chlorine resistance, more so than the conventional TFC membrane. In general, novel DA/TMC TFC membranes could be an effective strategy to synthesize high-performance FO membranes with excellent structural stability and chlorine resistance.

Combined Organic Fouling and Inorganic Scaling in Reverse Osmosis: Role of Protein-Silica Interactions

We investigated the relationship between silica scaling and protein fouling in reverse osmosis (RO). Flux decline caused by combined scaling and fouling was compared with those by individual scaling or fouling. Bovine serum albumin (BSA) and lysozyme (LYZ), two proteins with opposite charges at typical feedwater pH, were used as model protein foulants. Our results demonstrate that water flux decline was synergistically enhanced when silica and protein were both present in the feedwater. For example, flux decline after 500 min was far greater in combined silica scaling and BSA fouling experiments (55 ± 6% decline) than those caused by silica (11 ± 2% decline) or BSA (9 ± 1% decline) alone. Similar behavior was observed with silica and LYZ, suggesting that this synergistic effect was independent of protein charge. Membrane characterization by scanning electron microscopy and Fourier transform infrared spectroscopy revealed distinct foulant layers formed by BSA and LYZ in the presence of silica. A combination of dynamic light scattering, transmission electron microscopy , and energy dispersive X-ray spectroscopy analyses further suggested that BSA and LYZ facilitated the formation of aggregates with varied chemical compositions. As a result, BSA and LYZ were likely to play different roles in enhancing flux decline in combined scaling and fouling. Our study suggests that the coexistence of organic foulants, such as proteins, largely alters scaling behavior of silica, and that accurate prediction of RO performance requires careful consideration of foulant-scalant interactions.

Resistance of a multiple-isolate marine culture to ultraviolet C irradiation: inactivation vs biofilm formation

Ultraviolet (UV) irradiation is an emerging strategy for controlling the formation of undesired biofilms in water desalination facilities using reverse osmosis (RO). However, most studies examining these pretreatments are limited as they have been conducted on single-species cultures, while biofilms are composed of multiple-species communities. The goal of this study was to investigate the effect of UV-C irradiation on a model community composed of six environmental isolates from a marine biofilm formed in RO seawater desalination plant. There was a high variance in the susceptibility of the single-isolate cultures to UV-C, from no response (isolate Eryth23) to complete inactivation (isolate Vib3). The most active wavelength was around 260 nm, resulting in a loss of viability of single-isolate cultures and loss of vitality of the mixed-isolate cultures. With respect to biofilm formation, the activity of this wavelength was completely different compared to its activity on planktonic suspension. Irradiation with 260 nm did not inhibit the total biofilm formation by the six-isolate culture; moreover, isolates such as the resistant Eryth23 or the susceptible Pseudoalt17, even gained abundance in the mixed isolate biofilm. The only decrease in total biofilm was obtained from irradiation at 280 nm, which was less active against the planktonic culture. These results indicate that the complexity of the biofilm-forming microbial community may contribute to its resistance to UV-C irradiation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study examined the resistance of a multiple-isolate native marine culture to UV-C irradiation, in terms of viability, vitality and the ability to form biofilm. Results of this study showed that even though most of the cells were inactivated both in single-isolate and in multiple-isolate cultures, still the multiple-isolate cultures manages to form biofilms, surprisingly with higher biomass than without irradiation. The significance of the study is in its conclusion that studies on UV-C irradiation of biofilm-forming model micro-organisms are not always applicable to natural multiple-species communities.

Forward Osmosis Application in Manufacturing Industries: A Short Review

Forward osmosis (FO) is a membrane technology that uses the osmotic pressure difference to treat two fluids at a time giving the opportunity for an energy-efficient water and wastewater treatment. Various applications are possible; one of them is the application in industrial water management. In this review paper, the basic principle of FO is explained and the state-of-the-art regarding FO application in manufacturing industries is described. Examples of FO application were found for food and beverage industry, chemical industry, pharmaceutical industry, coal processing, micro algae cultivation, textile industry, pulp and paper industry, electronic industry, and car manufacturing. FO publications were also found about heavy metal elimination and cooling water treatment. However, so far FO was applied in lab-scale experiments only. The up-scaling on pilot- or full-scale will be the essential next step. Long-term fouling behavior, membrane cleaning methods, and operation procedures are essential points that need to be further investigated. Moreover, energetic and economic evaluations need to be performed before full-scale FO can be implemented in industries.

Application of forward osmosis technology in crude glycerol fermentation biorefinery-potential and challenges

Forward osmosis (FO) is a low energy-intensive process since the driving force for water transport is the osmotic pressure difference, Δπ, between the feed and draw solutions, separated by the FO membrane, where π_draw > π_feed. The potential of FO in wastewater treatment and desalination have been extensively studied; however, regeneration of the draw solution (thereby generating clean water) requires application of an energy-intensive process step like reverse osmosis (RO). In this study, the potential of applying FO for direct water recirculation from diluted fermentation effluent to concentrated feedstock, without the need for an energy-intensive regeneration step (e.g. RO), has been investigated. Butanol production during crude glycerol fermentation by Clostridium pasteurianum, has been selected as a model process and the effect of cross-flow velocity and the dilution of draw solution on the water flux during short-term experiments (200 min), were investigated. Statistical analysis revealed that the dilution of the draw solution is the most influential factor for the water flux. Subsequent modelling of an integrated FO-fermentation process, showed that water recoveries could lead to substantial financial benefits, although the integrated FO-fermentation process demonstrated lower water flux than expected. FTIR analyses of the membrane surface implied that the decrease in water flux was due to the presence of proteins, polysaccharides and other extracellular polymeric substances on the membrane active layer, indicating the presence of a fouling layer. Based on these findings, possible fouling alleviation strategies and future research directions are discussed and proposed.

Concentrating molasses distillery wastewater using biomimetic forward osmosis (FO) membranes

Treatment of sugarcane molasses distillery wastewater is challenging due to the presence of complex phenolic compounds (melanoidins and polyphenols) having antioxidant properties. Due to zero liquid discharge regulations, Indian distilleries continue to explore effective treatment options. This work examines the concentration of distillery wastewater by forward osmosis (FO) using aquaporin biomimetic membranes and magnesium chloride hexahydrate (MgCl₂.6H₂O) as draw solution. The operational parameters viz. feed solution and draw solution flow rate and draw solution concentration were optimized using 10% v/v melanoidins model feed solution. This was followed by trials with distillery wastewater. Under the conditions of this work, feed and draw flow rates of 1 L/min and draw solution concentration of 2M MgCl₂.6H₂O for melanoidins model solution and 3M MgCl₂.6H₂O for distillery wastewater were optimal for maximum rejection. Rejection of 90% melanoidins, 96% antioxidant activity and 84% COD was obtained with melanoidins model feed, with a corresponding water flux of 6.3 L/m²h. With as-received distillery wastewater, the rejection was similar (85-90%) to the melanoidins solution, but the water flux was lower (2.8 L/m²h). Water recovery from distillery wastewater over 24 h study period was higher with FO (70%) than reported for RO (35-45%). Repeated use of the FO membrane over five consecutive 24 h cycles with fresh feed and draw solutions and periodic cleaning showed consistent average water flux and rejection of the feed constituents.

Long-Term Stability of Low-Pressure Reverse Osmosis (RO) Membrane Operation—A Pilot Scale Study

Reverse osmosis (RO) elements operating at a low pressure (LP) or a low energy (LE) are generally called “LPRO” or “LERO”, and the nomenclature “LP” and “LE” are convertible due to the interrelated features of the pressure and the energy in the RO process. Not only can LPRO be operated at lower pressures, which enables energy saving, but also at the standard operating pressure with an enhanced permeate flux. In this study, the feasibility of the LPRO element was evaluated in the face of high fouling potential feed water. The commercially available standard RO and LPRO were chosen, and the membrane properties including the fouling susceptibility and the surface characteristics were thoroughly evaluated. The variations of various performance parameters were monitored during an 872 h operation in a pilot system, which was operated in a constant flux mode. Then, the used membranes were analyzed to further verify the fouling load localization and the fouling intensities. The average flux variation of the individual RO elements in a vessel and the economic feasibility of LPRO were also evaluated through a simulation study using an RO system design software. This study showed that the localization of fouling load within a pressure vessel of an LPRO system caused about 20% higher flux decline and almost 2-times higher salt passage than those of a standard RO membrane system. Furthermore, the simulation study predicted that average operating pressure difference ratio (%) between two RO membranes decreased from 24.4% to 17.8% and a substantial quantity of LPRO elements (83.3%) must be replaced to meet the designated water criteria only after 2 years’ operation.

Synthetic polymer materials for forward osmosis (FO) membranes and FO applications: a review

Forward osmosis (FO) has played an important role in alleviating the problems caused by freshwater shortage and water contamination in recent years. However, issues of low water permeability, reverse solute diffusion, concentration polarization and membrane fouling are still widely present in FO processes. These challenges are the current research focus in exploring novel FO membranes. Fabricating FO membranes from chemically modified commercial polymers is a relatively novel approach and has proven effective in obtaining appropriate FO membranes. This paper focuses on the progress of FO membranes made specially from chemically modified polymer materials. First of all, a brief overview of commercial polymers commonly used for FO membrane fabrication is provided. Secondly, the chemical modification strategies and synthesis routes of novel polymer materials as well as the resultant FO membrane performance are presented. The strengths and weaknesses of chemical modifications on polymer materials are assessed. Then, typical FO applications facilitated by the FO membranes made from modified polymer materials are exemplified. Finally, challenges and future directions in exploring novel polymers through chemical modifications for FO membrane fabrication are highlighted. This review may provide new insights into the future advancement of both novel membrane materials and FO membranes.

Porous nanocomposite membranes based on functional GO with selective function for lithium adsorption

An inorganic–organic composite membrane based on functional GO nanosheet for selective lithium adsorption from compound has great potential.

Synthetic draw solutes for forward osmosis: status and future

Forward osmosis (FO) has developed rapidly over the past decade. The development of draw solutes, a key component of FO processes, has also progressed remarkably. A wide range of synthetic draw solutes have been explored in recent years. Synthetic draw solutes exhibit superiority over the conventional draw solutes obtained commercially in terms of lower reverse solute fluxes and less energy consumption in draw solute recycling. However, there are still some big challenges for synthetic draw solutes, such as complicated synthetic procedures, low water fluxes, severe concentration polarization (CP) and decreased water recovery efficiency when recycled draw solutes are reused in FO. These challenges are also the current research focus on the exploration of novel draw solutes. This article aims to review the recent progress especially on synthetic draw solutes. Their design strategies, synthesis routes and FO performance are assessed. Some representative applications involving the synthetic draw solutes-facilitated FO processes are exemplified. The advantages and disadvantages of the existing synthetic draw solutions are evaluated. The challenges and future directions in exploring novel draw solutes are highlighted.