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© 2020 Elsevier B.V. Membrane distillation (MD) is an alternative membrane technology that offers the capacity to treat highly saline water including industrial wastewater, seawater, brine water from other processes, and oil-gas field produced water. However, conventional hydrophobic membranes suffer fast wetting and severe fouling especially when low surface tension chemicals exist in saline water, which compromises the performance of MD. Recent advances in material science and nanomaterials research have led to the incorporation of special wetting properties on membrane surfaces. Membranes with special wettability can achieve high resistance against membrane fouling and wetting, as well as overcome the trade-off between membrane permeability and selectivity. This review summarizes the progress and recent development of studies on MD membranes with special wettability. Firstly, the fundamental concepts pertaining to membrane surface wettability including insights of their benefits and potential issues are highlighted in this review. Secondly, fabrication methods and applications of membranes utilizing various special wettability are discussed in detail, along with their challenges. Finally, this review concludes the advantages of membranes with special wettability and demonstrates potential solutions to the above-mentioned challenges for future research in high saline wastewater treatment.

© 2017 Elsevier B.V. Membrane distillation (MD) is an attractive technology for seawater reverse osmosis (SWRO) brine treatment. Submerged MD (S-MD) offers an additional advantage of a compact system compared to cross-flow MD. This study evaluated the performances of three different S-MD configurations; submerged direct contact membrane distillation (S-DCMD), submerged vacuum direct contact membrane distillation (S-VDCMD) and submerged vacuum membrane distillation (S-VMD) for SWRO brine treatment. A 13–77% higher water flux was obtained by S-MDs with vacuum incorporation (S-VMD and S-VDCMD) compared to S-DCMD, attributed to higher driving force. Evaluation on the influence of feed concentration and permeate temperature revealed that S-MD with high vacuum was significantly affected by feed concentration. Meanwhile S-DCMD was more severely affected by feed temperature losses, based on the tendency of membrane pore crystallization formation. The crystallization tendency on the membrane surface was influenced by the presence of vacuum pressure. A repeated cycle of S-DCMD with membrane air-backwashing was effective for flux recovery and to reduce membrane crystallization, enabling to concentrate SWRO brine by 2.8 times of volume concentration factor.

© 2014 Elsevier Ltd. In this study gravity-driven membrane (GDM) ultrafiltration is investigated for the pretreatment of seawater before reverse osmosis (RO). The impacts of temperature (21±1 and 29±1°C) and hydrostatic pressure (40 and 100mbar) on dynamic flux development and biofouling layer structure were studied. The data suggested pore constriction fouling was predominant at the early stage of filtration, during which the hydrostatic pressure and temperature had negligible effects on permeate flux. With extended filtration time, cake layer fouling played a major role, during which higher hydrostatic pressure and temperature improved permeate flux. The permeate flux stabilized in a range of 3.6L/m2h (21±1°C, 40mbar) to 7.3L/m2h (29±1°C, 100mbar) after slight fluctuations and remained constant for the duration of the experiments (almost 3 months). An increase in biofouling layer thickness and a variable biofouling layer structure were observed over time by optical coherence tomography and confocal laser scanning microscopy. The presence of eukaryotic organisms in the biofouling layer was observed by light microscopy and the microbial community structure of the biofouling layer was analyzed by sequences of 16S rRNA genes. The magnitude of permeate flux was associated with the combined effect of the biofouling layer thickness and structure. Changes in the biofouling layer structure were attributed to (1) the movement and predation behaviour of the eukaryotic organisms which increased the heterogeneous nature of the biofouling layer; (2) the bacterial debris generated by eukaryotic predation activity which reduced porosity; (3) significant shifts of the dominant bacterial species over time that may have influenced the biofouling layer structure. As expected, most of the particles and colloids in the feed seawater were removed by the GDM process, which led to a lower RO fouling potential. However, the dissolved organic carbon in the permeate was not be reduced, possi

© 2014. Biofilm formation, one of the primary causes of biofouling, results in reduced membrane flux or increased transmembrane pressure and thus represents a major impediment to the wider implementation of membrane bioreactor (MBR) technologies for water purification. Most studies have focused on the role of bacteria in membrane fouling as they are the most dominant and best studied organisms present in the MBR. In contrast, there is limited information on the role of the archaeal community in biofilm formation in MBRs. This study investigated the composition of the archaeal community during the process of biofouling in an MBR. The archaeal community was observed to have lower richness and diversity in the biofilm than the sludge during the establishment of biofilms at low transmembrane pressure (TMP). Clustering of the communities based on the Bray-Curtis similarity matrix indicated that a subset of the sludge archaeal community formed the initial biofilms. The archaeal community in the biofilm was mainly composed of Thermoprotei, Thermoplasmata, Thermococci, Methanopyri, Methanomicrobia and Halobacteria. Among them, the Thermoprotei and Thermoplasmata were present at higher relative proportions in the biofilms than they were in the sludge. Additionally, the Thermoprotei, Thermoplasmata and Thermococci were the dominant organisms detected in the initial biofilms at low TMP, while as the TMP increased, the Methanopyri, Methanomicrobia, Aciduliprofundum and Halobacteria were present at higher abundances in the biofilms at high TMP.

© 2014, © 2014 Taylor & Francis. Biofouling, the combined effect of microorganism and biopolymer accumulation, significantly reduces the process efficiency of membrane bioreactors (MBRs). Here, four biofilm components, alpha-polysaccharides, beta-polysaccharides, proteins and microorganisms, were quantified in MBRs. The biomass of each component was positively correlated with the transmembrane pressure increase in MBRs. Proteins were the most abundant biopolymer in biofilms and showed the fastest rate of increase. The spatial distribution and co-localization analysis of the biofouling components indicated at least 60% of the extracellular polysaccharide (EPS) components were associated with the microbial cells when the transmembrane pressure (TMP) entered the jump phase, suggesting that the EPS components were either secreted by the biofilm cells or that the deposition of these components facilitated biofilm formation. It is suggested that biofilm formation and the accumulation of EPS are intrinsically coupled, resulting in biofouling and loss of system performance. Therefore, strategies that control biofilm formation on membranes may result in a significant improvement of MBR performance.

The heat and mass transfer resistances of fouling layers can cause a significant flux decline in a membrane distillation (MD) process. In addition, the hydrophilicity and microporous nature of a fouling layer can affect the driving force and correspondingly the flux in MD via curvature effects on the vapor pressure as described by the Kelvin equation. This study explores the effect of the hydrophilicity of the sludge on the particle size, vapor pressure and pore-size distribution (PSD) in the biofouling layer and on the permeation flux in cross-flow MD. Two sets of hydrophilic sludge cultures were selected via the Microbial-Adhesion-to-Hydrocarbon method. Cross-flow MD experiments conducted with these two sludges displayed a 60% reduction in the flux relative to using a Milli-Q water feed. However, there was no significant difference in the fluxes for the two sludges. Characterization of the pore-size distribution of the two sludges using evapoporometry, a novel technique based on the vapor-pressure depression caused by small pores, indicated a vapor-pressure depression of 31% and 21% for the more- and less-hydrophilic sludges, respectively. However the effect of the 10% difference in vapor-pressure depression, when combined with the effect of the biofouling layer on the heat- and mass-transfer resistances, could not be detected within the experimental error in this study. Nevertheless, a major conclusion is that the vapor-pressure depression caused by a biofouling layer, or other foulants, could cause a significant reduction in the driving force for MD. © 2013 Elsevier B.V.

Pseudomonas aeruginosa PAO1 wild type and a mucoid derivative (FRD1) which over produces alginate were used to foul reverse osmosis (RO) membranes. When operated at a constant flux, biofilm formation on the RO membrane resulted in a slow rise in transmembrane pressure (TMP) of 22% for the initial four days of operation, followed by a sharp increase of 159% over the following two days. The initial slow increase in TMP was probably due to the formation of a biofilm on the membrane surface, which then accelerated the rate of biofouling through the effect of concentration polarization. At later stages of operation, most of the bacterial biomass consisted of dead cells. The amount of extracellular polymeric substances appeared to correlate positively with the number of dead cells. The results indicate that prolonging the initial stage of slow TMP increase and avoiding the latter stage of accelerated TMP increase would provide a sustainable operation of the RO system. These results suggest that nutrient limitation could reduce biofilm accumulation and delay the increase in TMP. © 2013 Copyright Taylor and Francis Group, LLC.

The integration of forward osmosis (FO) and biological process, known as the osmotic membrane bioreactor (OMBR), may be viewed as beyond the state of the art for used water treatment and water reclamation. While it is known that the OMBR is able to produce good product water quality in terms of total organic carbon (TOC) removal, limited information is available on the removal of organic micro-pollutants in relation to process performance under the concentrated environment. In this study, a novel OMBR system was continuously operated over 73 days, during which pharmaceuticals were dosed on two occasions into the system. It was found that while pharmaceutical removal was high (>96%), other process parameters in the form of TOC, mixed liquor suspended solids (MLSS) and extracellular polymeric substances (EPS) were unmistakably affected. The major portion of TOC that permeated the FO membrane was found to be low-molecular weight neutral compounds which were associated with the impaired biological process. Microbiological analysis confirmed shifts in microbial populations occurred due to the increased salinity and dosage of the pharmaceuticals. The study demonstrated the importance of the biological process for optimal OMBR system performance, and paves the way for further research in this direction. © 2012 Copyright Taylor and Francis Group, LLC.

Biofouling has been traditionally described as biofilm development on the membrane surface and leads to an increase in the required trans-membrane pressure (TMP). This study focuses on the impact of the feed channel spacer on the extent and nature of biofouling on the membrane. Experiments were conducted under conditions of constant flux with different hydrodynamics and biofouling was measured by TMP rise. In addition, biofilm development in the spacer-filled channel was monitored by confocal laser scanning microscope (CLSM) to both correlate the increase in TMP with the amount of biofilm development as well as to compare biofilm development on the feed channel spacer and the membrane. Faster TMP rise was observed under higher flux, lower crossflow, and higher salinity conditions. The presence of the feed channel spacer had a positive impact in terms of reduction of TMP rise, and no significant increase in channel pressure drop was observed during the experiments. In order to reconcile these observations with other studies that emphasize the role of spacer fouling, the scenarios likely to lead to predominance of membrane fouling or spacer fouling are discussed. © 2012 Elsevier B.V.

Decentralized wastewater treatment has the potential to provide sanitation that meets criteria for sustainable urban water management in a manner that is less resource intensive and more cost effective than centralized approaches. It can facilitate water reuse and nutrient recovery and can potentially reduce the ecological risks of wastewater system failure and the community health risk in a wastewater reuse scheme. This paper examines the potential role of membrane technology in sustainable decentralized sanitation. It is argued that the combination of membrane technology within decentralized systems can satisfy many of the criteria for sustainable urban water management. In particular, the role of membranes as a dependable barrier in the wastewater treatment process can increase system reliability as well as lowering the latent risks due to wastewater reuse. The modular nature of membranes will allow plant size to range from single dwellings, through clusters to suburb size. It is concluded that realization of the potential for membrane-based technologies in decentralized wastewater treatment will require some progress both technically and institutionally. The areas where advances are necessary are outlined. © IWA Publishing 2005.

The orientation of hollow fibres (vertical or transversal) is of interest for the design of submerged hollow fibre modules. The purpose of this paper is to assess the effect of fibre orientation on performance for the filtration of biomass. A crossflow fibre cell was built to hold hollow fibres in well-controlled transverse or axial orientation. Two sizes of polypropylene hollow fibre, 0.65 and 2.7mm (o.d.) were tested. A microscope and video-camera system was used to monitor particle deposition on the fibres. Filtration experiments with and without bubbling were carried out using yeast as model particles. The experiments showed that the effect of fibre orientation on the filtration process depends on the system conditions (with or without bubbling, fibre diameter, etc.). For filtration without bubbling, the transverse flow resulted in about 50% enhancement in filtration performance for 0.65mm fibres but the benefits was insignificant for 2.7mm fibres. The different filtration behaviour between 0.65 and 2.7mm fibres in the filtration of biomass with transverse flow was attributed to the effect of wall shear around the transverse fibres, fibre movement, vortex formation, and inertial impaction. On the other hand, for filtration with bubbling, around 5-15% lower flux declines occurred with axial orientation for both 0.65 and 2.7mm fibres. Comparing the results obtained with and without bubbling, the effect of fibre orientation on filtration with the smaller fibre decreased with injection of air. This implies that for filtration with bubbling the process tends to be dominated by the turbulence caused by the two-phase flow. However, axial bubble flow, rather than transverse does promise better performance in the membrane filtration of biomass. © 2002 Elsevier Science B.V. All rights reserved.