A review of nanoparticle-enhanced membrane distillation membranes: membrane synthesis and applications in water treatment

Membrane distillation (MD) is a thermally driven process that uses low-grade energy to operate and has been extensively explored as an alternative cost-effective and efficient water treatment process compared to conventional membrane processes. MD membranes are synthesized from hydrophobic polymers, e.g. polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or polypropylene (PP), using various methods including phase inversion and electrospinning techniques. Recent literature on MD membranes clearly shows their important role in surface water/wastewater treatment and seawater desalination. Modification of MD membranes with nanoscale materials significantly improves their performance, preventing wetting and fouling. This review presents a critical assessment of the progress on the use of nanomaterials for the modification of MD membranes. The techniques commonly used to synthesize MD membranes, the modifications that have been adopted for the incorporation of nanomaterials onto membranes, and the unique properties these nanomaterials impart on the membranes are discussed. The use of modified membranes in different MD configurations and their application in groundwater, surface water, wastewater, brackish water and seawater treatment is reviewed. Finally, cost implications, commercial viability, environmental sustainability, and future prospects of MD are also discussed to elucidate promising approaches for a future and successful implementation of MD at an industrial scale. © 2019 Society of Chemical Industry     

Evaluation of Zosteric Acid for Mitigating Biofilm Formation of Pseudomonas putida Isolated from a Membrane Bioreactor System

This study provides data to define an efficient biocide-free strategy based on zosteric acid to counteract biofilm formation on the membranes of submerged bioreactor system plants. 16S rRNA gene phylogenetic analysis showed that gammaproteobacteria was the prevalent taxa on fouled membranes of an Italian wastewater plant. Pseudomonas was the prevalent genus among the cultivable membrane-fouler bacteria and Pseudomonas putida was selected as the target microorganism to test the efficacy of the antifoulant. Zosteric acid was not a source of carbon and energy for P. putida cells and, at 200 mg/L, it caused a reduction of bacterial coverage by 80%. Biofilm experiments confirmed the compound caused a significant decrease in biomass (−97%) and thickness (−50%), and it induced a migration activity of the peritrichous flagellated P. putida over the polycarbonate surface not amenable to a biofilm phenotype. The low octanol-water partitioning coefficient and the high water solubility suggested a low bioaccumulation potential and the water compartment as its main environmental recipient and capacitor. Preliminary ecotoxicological tests did not highlight direct toxicity effects toward Daphnia magna. For green algae Pseudokirchneriella subcapitata an effect was observed at concentrations above 100 mg/L with a significant growth of protozoa that may be connected to a concurrent algal growth inhibition.     

Experimental Study and Design of a Submerged Membrane Distillation Bioreactor

A hybrid process incorporating membrane distillation in a submerged membrane bioreactor operated at elevated temperature is developed and experimentally demonstrated in this article. Since organic particles are rejected by an ‘evaporation’ mechanism, the retention time of non‐volatile soluble and small organics in the submerged membrane distillation bioreactor (MDBR) is independent of the hydraulic retention time (mainly water and volatiles). A high permeate quality can be obtained in the one‐step compact process. The submerged MD modules were designed for both flat‐sheet membranes and tubular membrane configurations. The process performance was preliminarily evaluated by the permeate flux stabilities. The module configuration design and air sparging used in the MDBR process were tested. Flux declines were observed for the thin flat‐sheet hydrophobic membranes. Tubular membrane modules provided more stable permeate fluxes probably due to the turbulent condition generated from air sparging injected inside the tubular membrane bundles. The experiments with the submerged tubular MD module gave stable fluxes of approximately 5 L/m² h over 2 weeks at a bioreactor temperature of 56 °C. The total organic carbon in the permeate was consistently lower than 0.7 mg/L for all experiments.     

新型硅橡胶膜生物反应器用于有机废水处理的膜传质动力学

用中空纤维型硅橡胶管构造了管束式和卷绕式两种膜器,将它们结合进一个生物反应器系统,用于对废水中的挥发性有机化合物（VOC）进行生物降解处理。本文以甲苯为对象,研究了VOC在这种系统中穿过膜的传质问题。基于液-膜-液的串联阻力概念和质量平衡,构造了一个关于膜总传质系数的简单指数模型,用于传质实验的分析。将甲苯溶于水中模拟有机废水,配制适合于甲苯降解细菌生长的培养液,进行了甲苯从废水穿过膜到培养液中的传质实验,并将细菌移植进培养液进行了生物降解条件下的传质实验。对培养液中细菌存在和不存在两种情况下的甲苯传质实验进行了分析。结果表明,总传质系数的指数模型基本上与实验条件符合,所得到的甲苯的总膜传质系数具有10-6m·s-1数量级,卷绕膜器的总传质系数较管束型的稍高,生物反应条件下的总传质系数又较细菌不存在时的稍高。     

Biofouling alleviation and flux enhancement of electrospun PAN microfiltration membranes by embedding of para‐aminobenzoate alumoxane nanoparticles

Membrane bioreactor (MBR) as a hybrid technology for wastewater treatment is becoming more popular for wastewater treatment. However, membrane fouling has hindered the widespread application of MBRs. Many efforts have been done for fouling mitigation. In this study, high flux and antifouling microfiltration membranes with unique surface structure, high surface porosity, and permeability were prepared by electrospinning technique. Initially, the optimum thickness of electrospun polyacrylonitrile (PAN) membranes was determined and then, electrospun PAN membrane at optimum thickness were prepared by embedding para‐aminobenzoate alumoxane (PABA) nanoparticles at different concentrations. The effect of PABA nanoparticles on membrane performance was investigated. To investigate the characterization of the prepared membranes Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy, and water contact angle measurement were employed. The flux recovery ratio results revealed that the antifouling properties of the electrospun PAN membrane were enhanced by modification. The 3 wt % electrospun PABA embedded PAN had the best permeability, hydrophilicity, and antifouling properties among the fabricated membranes and showed remarkable reusability during filtration. The results obtained suggested that the high flux and antifouling electrospun PAN membranes embedded PABA nanoparticles could be used as MBR membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45738.     

Behavior of Membrane Scaling During Crossflow Filtration in the Anaerobic MBR System

Abstract

Fouling of membrane bioreactor (MBR) has been studied intensively. Because of the high concentration of carbonates, scaling can be a serious problem in anaerobic bioreactor, which attracts little attention. In this study, the wastewater was treated with an anaerobic process followed by either a submerged or a side‐stream aerobic membrane reactor. The wastewater was spiked with calcium to investigate the effect of scaling on membrane filtration. Very little scaling was detected in the external membrane system (the side‐stream MBR). Results from chemical cleaning of internal membrane system indicated that the flux decline caused by membrane scaling was far more severe than that by membrane fouling. However, the flux decline from membrane scaling can be effectively recovered by the chemical cleaning of EDTA and NaOCl.     

Treatment of metal‐containing wastewaters with a novel extractive membrane reactor using sulfate‐reducing bacteria

This work reports a novel system for the treatment of acidic metal‐containing wastewaters, the Extractive Membrane Bioreactor–Sulfate‐Reducing Bacteria (EMB‐SRB) system. In this system, hydrogen sulfide is produced in the bioreactor by the sulfate‐reducing bacteria, transfers through a dense phase membrane, and precipitates metal ions in the wastewater. The non‐porous membrane prevents the SRB from having direct contact with the toxic metals, extremes of pH, or high salinity in the wastewater. Silicone rubber, which is permeable to H₂S but virtually impermeable to ionic species in the system, was used as a membrane. The rate of mass transfer of H₂S across the membrane was studied and found to be well described by a resistances‐in‐series model. k_ov values vary in the range 5 × 10⁻⁶ –10 × 10⁻⁶ ms⁻¹ 1 depending on the membrane thickness. A continuous EMB–SRB system was operated and more than 90% (w/v) of the Zn²⁺ present in a wastewater was removed. A film of metal precipitate was found to build up on the inside (wastewater) side of the membrane, and became the dominant resistance contributing to the overall mass transfer coefficient during operation. © 2001 Society of Chemical Industry     

Biological treatment of saline wastewater using a salt-tolerant microorganism

Biological aerobic treatment of saline wastewater provides the material of this study. A salt-tolerant microorganism (Staphylococcus xylosus) was isolated from a vegetable pickled plant containing about 7.2% salt. Selection, identification and characterization of the microorganism were carried out. The isolated microorganism was used as inoculum for biodegradation. An activated sludge reactor operated in a fed-batch mode was used for the treatment of synthetic saline wastewater using three different microbial cultures namely: activated sludge (100%), a mixture of Staphylococcus supplement by activated sludge (1:1) and pure S. xylosus (100%) at different salt concentrations ranging from 0.5 to 3% NaCl. The results obtained showed that at low NaCl concentration (1%), the removal efficiency of chemical oxygen demand (COD) using different microbial cultures were almost the same (80-90%). However, increasing the NaCl concentration to 2% and using Staphylococcus-supplemented mixture by activated sludge and S. xylosus alone improved the treatment performance as indicated by COD removal rates which reached 91% and 93.4%, respectively, while the system performance started to deteriorate when activated bacterial culture was used alone (74%). Furthermore, the increase in NaCl concentration up to 3% and with the inclusion of Staphylococcus-supplemented mixture by activated sludge increased the COD removal to 93%, while the use of S. xylosus alone further improved the COD removal rate up to 94%. Also, the use of S. xylosus alone proved to be capable for biological treatment of a real case study of a vegetable pickled wastewater containing 7.2% salinity; the removal efficiency of COD reached 88% at this very high concentration of NaCl.     

Evaluation of the antifouling and photocatalytic properties of novel poly(vinylidene fluoride) membranes with a reduced graphene oxide–Bi2WO6 active layer

Immobilization of reduced graphene oxide (RGO)–Bi₂WO₆ is an ideal method for obtaining antifouling membranes for membrane distillation (MD) processes. Poly(vinylidene fluoride) membranes modified with RGO–Bi₂WO₆ were successfully obtained with a double‐layer coating method through non‐solvent‐induced phase separation. The water contact angle was improved by about 30° by RGO–Bi₂WO₆; this indicated that the surface modification obviously increased the membrane hydrophobicity. The high desalination rate proved that all of the prepared membranes were appropriate for the MD process. The RGO–Bi₂WO₆‐modified membranes achieve 26.26%–59.95% removal rates in 10 mg/L aqueous ciprofloxacin under visible light for 7.5 h. It was possible to erase strongly bound foulants and recover the prepared membrane's permeation flux by 3 h of visible‐light irradiation. The RGO–Bi₂WO₆‐modified membrane with a high hydrophobicity, fouling mitigation, and photocatalytic capability presents huge potential for the treatment of high‐salt antibiotic wastewater use in the MD process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45426.     

Surface modifications of polypropylene membranes used for blood filtration

The surface of two commercial meltblown polypropylene (PP) membranes, used for the filtration of blood products, were modified by wet chemistry treatments (carbodiimide, tosyl chloride and trihalogeno-triazines) in the case of the oxygen-plasma treated membrane (O₂-PP), and by photochemistry using molecular clips in the case of the native PP membrane. The most efficient technique uses trifluoro-triazine reagent for the activation of both hydroxyl- and carboxyl-functions of O₂-PP. It enables the fixation of amine-terminated molecules with high degrees of derivatization (∼700 pmol/cm²), without inducing modification of the membrane morphology nor cytotoxicity. Only a weak decrease of surface hydrophilicity was measured after the treatments and steam-sterilization. This method was applied for the grafting of peptides (Gly-Gly-Gly-Gly-Gly, Gly-Arg-Gly-Asp-Ser, home-made modified Leu-Asp-Val) on O₂-PP membranes incorporated into multi-layer filter devices. These modified filters showed improved properties of leukocyte depletion in blood filtration experiments, principally due to the wetting properties of the membranes.     

Bacterial Community Structure on Membrane Surface and Characteristics of Strains Isolated from Membrane Surface in Submerged Membrane Bioreactor

Abstract

In order to investigate the bacterial community structure and the characteristics of bacteria on the membrane surface, a submerged membrane bioreactor treating municipal wastewater was continuously operated under two different conditions. Bacterial community structures were examined by PCR‐denaturing gradient gel electrophoresis and PCR cloning of 16S rRNA genes. Bacterial strains isolated from membrane surface were identified and their growth curve, EPS concentration and hydrophobicity were measured. The structures of bacterial communities in the suspended solids and on the membrane surface were obviously different, and γ‐Proteobacteria more selectively adhere and grow on the membrane surface than other microorganisms. Most of the membrane isolates grew slowly as compared with the strains isolated from the suspended solids. Also, the membrane isolates were higher cell surface hydrophobicities, higher EPS concentrations, and higher ratios of protein to carbohydrate within the EPSs than the isolates from suspended solids.     

高盐有机废水处理技术研究新进展

  随着工业的发展,大量排放的高盐有机废水对环境产生非常不利的影响。本文对传统的物理化学方法处理高盐废水进行总结,重点论述了膜分离技术在高盐有机废水处理中的应用。同时指出生物法（好氧生物法、厌氧生物法和好氧/厌氧组合工艺）被广泛地用于高盐有机废水的处理,其处理性能主要取决于嗜盐微生物的培养和驯化。在综合分析的基础上,指出高效能氧化剂的研制、性价比优良膜的制备、嗜盐菌的快速驯化和新型生物反应器的开发是高盐有机废水处理技术中的热点研究问题,物理化学法和生物法的组合工艺是高盐有机废水处理的研究方向。     

Fouling control in activated sludge submerged hollow fiber membrane bioreactors

The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid—liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH₄)₂SO₄ as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mg/L. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.     

Polypropylene surface with antibacterial property by photografting 1-vinylimidazole and subsequent chemical modification

The surface of polypropylene (PP) fiber was modified by UV-induced graft polymerization of 1-vinylimidazole (Vim), followed by quaternization with iodomethane, sulfonation with chlorosulfonic acid, or loading of silver (Ag) nanoparticles to endow the surface with antibacterial properties. The modified PP fibers were characterized by FT-IR, SEM, and surface charge analyses. The antibacterial activity of the modified PP fibers was assessed against the Gram-negative and Gram-positive bacteria, Escherichia coli (E. coli), and Staphylococcus aureus (S. aureus), respectively. The PP-g-Vim was greatly improved by loading of Ag nanoparticles (≥99.9%), quaternization (98.9–99.2%), or sulfonation (≥99.9%).     

Exploring the spinning and operations of multibore hollow fiber membranes for vacuum membrane distillation

Hollow fiber membranes with a multibore configuration have demonstrated their advantages with high mechanical strength, easy module fabrication, and excellent stability for membrane distillation (MD). In this work, the microstructure of multibore fibers was optimized for vacuum MD (VMD). A microstructure consisting of a tight liquid contact surface and a fully porous cross‐section is proposed and fabricated to maximize the wetting resistance and VMD desalination performance. The new membrane exhibited a high VMD flux of 71.8 L m^?2 h^?1 with a 78°C model seawater feed. Investigations were also carried to examine various effects of VMD operational conditions on desalination performance. The 7‐bore membrane showed higher flux and superior thermal efficiency under the VMD configuration than the direct contact MD configuration. Different from the traditional single‐bore hollow fiber, the VMD flux of multibore membrane at the lumen‐side feed configuration was higher than that of the shell‐side feed due to the additional evaporation surface of multibore geometry. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1078–1090, 2014     

Biocidal Activities of Cationic Surface Active Starch and Its Transition Metal Complexes Against Different Bacterial Strains

Starch alkyl triethanolammonium chloride derivatives and their metal complexes (Cu²⁺, Co²⁺ and Fe³⁺) were prepared and characterized using elemental analysis, FTIR, and ¹H-NMR spectra. The synthesized compounds were evaluated as antimicrobial agents against different microorganism including bacteria (gram +ve and gram −ve) and fungi. The effect of the chemical structure of the targeted cationic surfactants was discussed based on the surface parameters including surface tension and critical micelle concentration (CMC). Also, the effect of the structure of these surfactants and their metal complexes of Cu²⁺, Co²⁺ and Fe³⁺ on the cell membrane is discussed as well as their potent action on the targeted bacteria and fungi.     

Enhanced the antifouling and antibacterial performance of PVC/ZnO-CMC nanoparticles ultrafiltration membrane

Inorganic nanoparticles (NPs) have been employed in modification for polyvinyl chloride (PVC) membrane intrinsic hydrophobicity. Carboxymethyl chitosan (CMC), a natural organic matter, was used to relieve the agglomeration of zinc oxide (ZnO) NPs in the membrane matrix. In this paper, ZnO-CMC NPs were successfully prepared via co-precipitation approach, blended with PVC membranes, and the effect of ZnO-CMC NPs for the membrane properties was studied. The SEM and EDX confirmed excellent dispersion of ZnO-CMC NPs on the membrane surface. The enhanced hydrophilicity, porosity and inter-connected finger-like strcture of modified membranes confirmed by water contact angle and SEM. In addition, pure water flux of PVC/ZnO-CMC composite membrane was 107.36 L m⁻² h⁻¹ (PVC/ZnO-CMC (0.25 wt%)), which was higher than that of neat PVC membrane (83.11 L m⁻² h⁻¹). Importantly, the modified membranes exhibits lower static BSA adsorbtion because of the improved hydrophilicity, and a higher flux recovery rate (>90%) after three sequential filtration cycles. The antibacterial behavior of PVC/ZnO-CMC membrane was tested simply using Escherichia coli, and the results indicated that all composite membranes possess excellent antibacterial properties. Our work presents PVC/ZnO-CMC NPs composite membrane a promising future in wastewater treatment and antibacterial application.     

厌氧膜生物反应器在污水处理中的研究进展

综述了厌氧膜生物反应器中的微生物种群与分布特点、厌氧膜生物反应器在污水处理中的应用情况,讨论了影响厌氧膜生物反应器性能的主要参数、膜的污染预防与控制等,最后探讨和展望了厌氧膜生物反应器的应用前景,并指出了该领域今后的研究方向。     

Characterization of microbial communities in a fluidized-pellet-bed bioreactor for wastewater treatment

In order to make clear the microbiological characteristics of the fluidized-pellet-bed bioreactor (FPB) which is a newly developed wastewater treatment device to perform coagulation, particle pelletization, biological degradation and solid-liquid separation in a single unit, the method of denaturing gradient gel electrophoresis (DGGE) was applied in this study paying attention to the microbial diversity of the granular sludge. Spread plate method was also used for enumeration of aerobic bacteria in unit weight of granular sludge. As a result, slight difference was found between the total aerobic bacteria at the bottom, middle, and top sections though the dissolved oxygen (DO) concentration decreased from about 3.5 mg/L at the bottom inlet to 0.23 mg/L at the top of the FPB bioreactor. From the DGGE finger printing, 17 common species were identified from all these sections, and certain specific species were also identified from each section. The comparability of the microbial communities in the three sections was 83.1%, indicating a very stable structure of the microbial communities. The 16 S rRNA sequence analysis results revealed that the 18 operational taxonomic units (OTUs) obtained all belong to Eubacteria. Among them 11 are Proteobacteria, 3 are Actinobacteria, 2 are low G + C gram-positive bacteria and the remaining 2 belong to other bacteria branches. The dominant microbial communities are typical aerobes or facultative anaerobes commonly encountered in conventional activated sludge.     

Investigation of the Efficiencies of Bioaerosol Samplers for Collecting Aerosolized Bacteria Using a Fluorescent Tracer. II: Sampling Efficiency and Half-Life Time

Using uranine as a physical tracer, this study assessed the sampling efficiencies of four bioaerosol samplers (Andersen 6-stage impactor, all glass impinger “AGI-30,” OMNI-3000, and Airport MD8 with gelatin filter) for collecting Gram-positive bacteria (Enterococcus faecalis), Gram-negative bacteria (Escherichia coli and Campylobacter jejuni), and bacteria without cell wall (Mycoplasma synoviae) which were aerosolized in a HEPA isolator. In addition, the half-life times of these bacteria in aerosols were estimated. The uranine concentrations collected by the samplers were used for calculating the physical efficiencies, and the bacteria/uranine ratios were used for calculating the biological efficiencies. The results show the Airport MD8 had the highest physical efficiency. Compared with the Airport MD8, the physical efficiencies of the AGI-30 and the OMNI-3000 were 74% and 49%, respectively. A low physical efficiency of the Andersen impactor (18%) was obtained, but it was mainly caused by the incomplete recovery of uranine when handling the air samples, so could not be ascribed to the sampler efficiency. Both the Andersen impactor and the AGI-30 showed high biological efficiencies for all four bacterial species. The biological efficiencies of the OMNI-3000 for C. jejuni (1%) and of the Airport MD8 for E. coli (38%) and C. jejuni (2%) were significantly lower than 100%, indicating that their sampling stresses inactivated the bacterial culturability. The half-life times at 21–23°C temperature and 80–85% relative humidity were 43.3 min for E. faecalis, 26.7 min for M. synoviae, 21.2 min for E. coli, and 4.0 min for C. jejuni in the air.