Extractive Membrane Bioreactor Research Articles

Membrane biofouling mitigation via immobilizing AgNPs@ZIF-8 microcapsules on membrane surface for extractive membrane bioreactor

During the extractive membrane bioreactor (EMBR) process, the membrane mass transfer efficient would be significantly reduced due to the biofilm aggregation on the membrane surface. In order to mitigate the membrane biofouling, the microcapsules developed by encapsulating silver nanoparticles (AgNPs) into the zeolitic imidazolate framework-8 (ZIF-8), were immobilized on the membrane surface for the first time. The AgNPs@ZIF-8 microcapsules could ensure the well compatibility between the micromaterials and membrane surface, avoid direct exposure of AgNPs to biomass, as well as slowly release the silver ions on the membrane surface. Compared to the unmodified membrane #M0 (declined to 55% of its initial value) and ZIF-8 modified membrane #M1 (declined to 80% of its initial value), the AgNPs@ZIF-8 microcapsules-coated membrane #M2 displayed the best anti-biofouling performance with a stabilized phenol mass transfer coefficient of 31.04 × 10–7 m/s (96% of its initial value) after 14-days EMBR testing. Its excellent anti-biofouling property should be attributed to the electrostatic repulsion between membrane surface and microorganisms, antibacterial effects from ZIF-8, improved phenol affinity of the membrane, reduced membrane hydrophobicity, stable released silver ions, broad-spectrum bactericidal properties of the silver ions and reactive oxygen species.

Mitigation of membrane biofouling via immobilizing Ag-MOFs on composite membrane surface for extractive membrane bioreactor

The extractive membrane bioreactor (EMBR) combines an extractive membrane process and bioreactor to treat highly saline recalcitrant organic wastewater, in which the organic contaminations diffuse through a semi-permeable polydimethysiloxane (PDMS) composite membrane from the feed wastewater to the receiving biomedium. During the long-term EMBR operation, membrane biofouling is an inevitable phenomenon, which is one of the main obstacles impeding its wide applications. The excessive biofilm deposited on membrane surface could significantly reduce the organic mass transfer coefficient of composite membranes by more than 40%. Therefore, in this work, the silver (Ag)-metal organic frameworks (MOFs) were synthesized and immobilized on the PDMS surface of nanofibrous composite membranes to mitigate the membrane biofouling. The robustness of Ag-MOFs coating on membrane surface was well demonstrated by ultrasonic treatment. In addition, the silver nanoparticles (AgNPs) were coated on the PDMS surface of composite membranes for comparison. In contrast with the unmodified composite membrane #M0, the AgNPs-coated (#M1) and Ag-MOFs modified (#M2) composite membranes possessed less hydrophobic and negatively charged surfaces due to the coating layers. Although the modified membranes exhibited lower phenol mass transfer coefficients (k0’s) in the aqueous-aqueous extractive membrane process due to these additional modification layers, both #M1 and #M2 displayed better long-term performance in the 12-days continuous EMBR operations due to their excellent anti-biofouling properties. Moreover, #M2 exhibited the most stable EMBR performance among the composite membranes developed in this work and other reported membranes with a finally stabilized k0 of 33.0 × 10–7 m/s (89% of initial k0). The least amounts of proteins, polysaccharides and total suspended solids (TSS) on the surface of tested #M2 also demonstrated its outstanding biofouling resistance. This excellent anti-biofouling performance should be attributed to the stable, controlled and long-lasting Ag+release from Ag-MOFs, as well as its less hydrophobic and negative charged surface properties, which made #M2 undergo the k0’s increasing and gradual stabilization stages in the long-term EMBR operations.

Improvement of phenol separation and biodegradation from saline wastewater in extractive membrane bioreactor (EMBR)

Extractive membrane bioreactor (EMBR) is a promising technology for phenol saline wastewater treatment. In this work, an electrospun polydimethylsiloxane/polymethyl methacrylate/multi-walled carbon nanotubes (PDMS/PMMA/MWCNTs) membrane was firstly used in EMBR. To address low phenol transmembrane mass transfer issue, effects of wastewater condition (1.3–5.5 L/h circulation rate, 1000–4000 mg/L phenol), biomass addition (without/with pre-acclimated activated sludge) and biofilm formation (50.5–120.7 μm) were investigated. Membrane characterizations confirmed that biofilms on membrane surface gradually developed under increasing phenol concentrations, with simultaneously increased thickness and extracellular polymeric substances (EPS) excretion. Results showed phenol transmembrane mass transfer rates with activated sludge and formed biofilm increased 21.6–31.7% compared to those without activated sludge. Finally, 100% removal of permeated phenol and 99.96% rejection of salt were achieved under wastewater circulation rate of 4.4 L/h with 1000–4000 mg/L phenol and 10 g/L sodium chloride. Relevant findings are of significance in promoting the EMBR application in organic-inorganic composite wastewater treatment.

Extractive membrane bioreactor to detoxify industrial/hazardous landfill leachate and facilitate resource recovery

Landfill leachate is a highly polluted and toxic waste stream harmful to the environment and human health, its biological treatment, even if challenging, offers the opportunity of recovering valuable resources. In this study, we propose the application of an extractive membrane bioreactor equipped with a polymeric tubing, made of Hytrel, as an innovative device able to remove specific organic toxic compounds of the leachate and, at the same time, to produce an effluent rich in valuable chemicals suitable for recovery. The leachate treatment consists in a two-step process: the extraction of specific toxic compounds through the polymeric tubing based on the affinity with the polymer, and their subsequent biodegradation in controlled conditions in the bulk phase of the extractive membrane bioreactor, thus avoiding the direct contact of the microbial consortium with the toxic leachate. Three synthetic streams simulating leachates produced by landfills of typical industrial/hazardous waste, mixed municipal and industrial solid waste, and oil shale industry waste, whose toxic fraction is mainly constituted by phenolic compounds, have been tested. Successful performance was achieved in all the tested conditions, with high removal (≥98%) and biodegradation efficiencies (89–95%) of the toxic compounds. No mass transfer limitations across the tubing occurred during the operation and a marginal accumulation (in the range of 4–7%) into the polymer has been observed. Furthermore, volatile fatty acids and inorganic compounds contained in the leachates were fully recovered in the treated effluent. Feasibility study confirmed the applicability of the proposed bioreactor as a powerful technology able to achieve high toxic removal efficiency in leachate treatment and facilitate resource recovery.

Extractive membrane bioreactor (EMBR): Recent advances and applications

Combining bioreactor and membrane, known as a membrane bioreactor (MBR), has been considered as an attractive strategy to solve the limitations of conventional activated sludge process, such as biological instability, poor sludge quality, and low concentration of mixed liquor suspended solid. Unlike the other MBRs, extractive membrane bioreactor (EMBR) focuses on enhancing the efficiency of wastewater treatment through toxic compounds extraction by using a selective membrane. Even though EMBR has been successfully demonstrated in wastewater and waste gas treatment by several studies, it still faces some obstacles such as biofilm formation and low selectivity of the membrane towards a specific component. Appropriate biofilm formation control strategies and membrane with high selectivity are needed to solve those problems. This paper reviews EMBR including its potential applications in wastewater treatment, denitrification process, and waste gas treatment. In addition, challenges and outlook of EMBR are discussed.

High-performance electrospinning-phase inversion composite PDMS membrane for extractive membrane bioreactor: Fabrication, characterization, optimization and application

This study introduced a facile approach for high-performance electrospinning-phase inversion composite membrane, aiming at solving the low mechanical property, low mass transfer and salt leakage in extractive membrane bioreactor (EMBR) for phenol saline wastewater treatment. Composite membrane was fabricated through coating polydimethylsiloxane (PDMS) on electrospun PDMS membrane via dry phase inversion. Its surface was similar to that of phase inversion membrane while the cross section was uniformly distributed electrospun fibers in phase inversion layer, forming interconnected pore. The loose porous structure and high porosity were suitable for phenol permeation, and hydrophobic surface could reject the salt invasion. The tensile strength and elongation at break of composite membrane (56.5 μm thickness) were 1.7 MPa and 60.0%, making it stably operated in EMBR. Effects of different process variables were investigated, including membrane thickness, phenol concentration and wastewater flow rate. Remarkable performance of phenol biodegradation and salt rejection was achieved during EMBR operation, where the maximal phenol removal rate and conductivity variation in microorganism side were 508.9 mg L−1 d−1 and <0.1 ms cm−1, respectively. The highest phenol mass transfer coefficient of 8.8 × 10−7 m s−1 was achieved. It is reasonable to believe that this study fabricate a promising alternative membrane for EMBR application.

Novel external extractive membrane bioreactor (EMBR) using electrospun polydimethylsiloxane/polymethyl methacrylate membrane for phenol-laden saline wastewater

Phenol-laden saline wastewaters can adversely affect water, groundwater, soil, organisms and ecosystems. Given that frequently-used biodegradation process is generally inhibited by salinity, this work aims to solve the problem through a novel configuration of external extractive membrane bioreactor (EMBR) for the objective of simultaneous phenol permeation, salt rejection and biodegradation. Contact angles of 160.9 ± 2.2° (water) and 0.0° (phenol) were observed on the electrospun polydimethylsiloxane/polymethyl methacrylate (PDMS/PMMA) membrane, suggesting this superhydrophobic/superorganophilic membrane was suitable for separating phenol from water-soluble salt. Phenol ranging from 14.1 ± 2.7 to 290.7 ± 10.4 mg/L (stages 1 to 8) was continuously permeated and completely biodegraded in external EMBR under a hydraulic retention time (HRT) of 24 h, which corresponded with detoxification performance improving from 6.3% to 70.5%. After phenol exposure of 8 stages, Proteobacteria and Saccharibacteria became the main phyla for microorganisms. Enumeration of functional genes (phe, amoA, narG, nirS) confirmed that phenol was mainly consumed by denitrifiers and other heterotrophs as the sole carbon and energy source via oxidation and ring cleavage. As bacterial responses, these genes’ proliferation was promoted under low phenol concentrations but inhibited under high phenol concentrations. Meanwhile, results of extracellular polymeric substances revealed that protein was the key substance in toxicity resistance, phenol adsorption and transfer.

Operational behavior of a hydrogen extractive membrane bioreactor (HEMB) during mixed culture acidogenic fermentation

Fermentative hydrogen production requires a continuous products-removal and effective upgrading steps to improve its general performance. Therefore, implementation of new technologies capable of achieving both requirements is essential. We present the operational behavior of a new process concept based on integration of membranes for gas separation and fermentation technology. This process, which we term as hydrogen extractive membrane bioreactor consists of coupling two dense polymeric membranes to a hydrogen producing culture. The process automatization of this system was essential to maintain the proper operational pressures in the membrane module and in the bioreactor-gas-phase. This system was able to extract and partially separate the hydrogen and carbon dioxide generated. The hydrogen partial pressure was reduced from 55.5 to 49 KPa, which means an increase of hydrogen yield of 16.3% (1.1–1.28 mol-H2/mol-glucose). Simultaneously, the implemented system generated a final hydrogen stream 13% (v/v) more concentrated than a conventional process.

The biological treatment of synthetic fracking fluid in an extractive membrane bioreactor: Selective transport and biodegradation of hydrophobic and hydrophilic contaminants.

The biodegradation of selected organic constituents present in hydraulic fracturing wastewater were examined in an extractive membrane bioreactor (EMB) operating with Hytrel™ 3548 tubing. Synthetic hydraulic fracturing wastewater was generated via an extensive literature review and contained high concentrations (1000 mg L-1) of contaminant compounds of varied hydrophobicity, viz. methyl ethyl ketone, benzene, phenol and acetic acid, as well as 30-120 g L-1 of Cl- at low pH. This hostile wastewater was circulated through the polymeric tubing, selectively transporting the organic compounds through the membrane for biological degradation by an enriched bacterial consortium. 16S rDNA analysis revealed the presence of five dominant microbial strains within the consortium, including: Pseudomonas sp., Comamonas sp., Achromobacter sp., Lysinibacillus sp., and Oxalobacter sp. EMBs in batch operation achieved 99% removal of methyl ethyl ketone, benzene, and phenol after 72 h and effectively removed acetic acid up to its ionization point. Continuous EMB operation provided 99% removal of benzene and phenol, 96% removal of methyl ethyl ketone, and 53% of acetic acid. The treatment of synthetic hydraulic fracturing fluid demonstrated the effectiveness of carefully selected amphiphilic polymers in EMBs for treating the hydrophilic and hydrophobic organic profile found in hydraulic fracturing wastewaters.

Characterization of transport through polymers for fracking fluid treatment and organic acid concentration in extractive membrane bioreactors

AbstractBACKGROUNDThe water‐intensive practice of hydraulic fracturing produces wastewater containing a variable matrix of organic and inorganic compounds, including ions and ionizable organic compounds. Extractive membrane bioreactors (EMBs) operating with tailored polymer membranes can selectively sequester and/or transport these solutes for biological treatment. Four grades of Hytrel™ tubing were compared for their suitability in EMB systems, based on the polymers' thermodynamic affinity for solutes and their ability to transport or speciate ionic wastewater constituents.RESULTSOf the four Hytrel™ grades compared, high water content types (30% and 54% equilibrated water content) facilitated the transport of ionic species through the tubing, with all monovalent species being transported through both high‐water content grades, and lack of transport through the low‐water content tubing (3% and 5%). Undissociated organic acids were transported through all tubing types and dissociated acids were able to permeate only high‐water content grades. Using this differential ability to transport/not transport an organic acid depending on its dissociation state, a low‐water content Hytrel™ grade of tubing was able to concentrate a dilute butyric acid solution by 220% after 48 h.CONCLUSIONThe use of polymeric tubing for EMB applications for the treatment of hydraulic fracturing wastewater requires knowledge of both solute affinity and water content for complex waste streams, both of which affect the capability to transport organic and ionic species. © 2018 Society of Chemical Industry

Effects of internal concentration polarization and membrane roughness on phenol removal in extractive membrane bioreactor

Recent studies have proved the advantages of novel composite membranes in the extractive membrane bioreactor (EMBR) for recalcitrant organic wastewater treatment. However, more systematic research into membrane properties and mass transfer effects are required. This study investigates the role of internal concentration polarization (ICP), including concentrated and diluted ICP, in an aqueous-aqueous extractive process, and the coupled effects of membrane roughness and hydrodynamic conditions on membrane performance in both cross-flow EMBR (CF-EMBR) and submerged EMBR (S-EMBR) processes. To study these factors, a nanofibrous composite membrane with a four-tiered structure, consisting of a dense polydimethylsiloxane (PDMS) selective layer, a polyvinylidene fluoride (PVDF) nanofibrous sublayer, a non-woven mechanical support and a rough micro/nano-beaded layer, has been developed for the EMBR by electrospinning and spray-coating.A diluted ICP, which occurred when the selective layer faces receiving water (SL-Rw), was less severe than a concentrated ICP in the selective layer facing feed (SL-F) orientation. It resulted in higher overall membrane mass transfer coefficients (k0's) in the SL-Rw mode during the aqueous-aqueous extractive tests. In addition, less biofilm was observed on the smooth PDMS surface after 14-days CF-EMBR and S-EMBR operations in the selective layer facing biomedium (SL-Rbio) mode. In contrast, in the SL-F mode during EMBR operations, the ridges and valleys on the membrane surface were able to provide a more favourable micro-environment for microorganisms and protect them from external stresses. The mature micro-colonies that developed in the SL-F mode clogged the membrane support and enhanced concentrated ICP, resulting in a significant reduction of k0's by more than 58%. Moreover, as the shear force on the membrane surface due to up-flow of air bubbles in the S-EMBR could mitigate the biofilm attachment, the most effective biofilm control strategy found in this study was to operate the nanofibrous composite membrane in the S-EMBR configuration with a smooth selective layer facing the biomedium. This effectively decreased the amounts of protein by 86%, polysaccharides by 88% and total suspended solids (TSS) by 89% in the biofilms on membrane surface, and achieved the highest stable k0 of 7.0 × 10−7 m/s.

Design, development and evaluation of nanofibrous composite membranes with opposing membrane wetting properties for extractive membrane bioreactors

Extractive membrane bioreactors (EMBRs) are promising wastewater treatment processes combining an aqueous-aqueous extractive membrane process and biodegradation. The target contaminants diffuse through an extractive membrane and are metabolized by the active biofilm attached on the downstream membrane surface and microorganisms in the bioreactor. The benefit of EMBRs is that the biomass is not exposed to the potentially hostile feed conditions (high salinity, pH extremes etc.). The physicochemical properties of membrane surfaces on the receiving side facing the bioreactor are critical in controlling the extent and nature of the membrane-attached biofilm. In this work, novel nanofibrous composite membranes with a superhydrophobic surface (coded as NC) or a superhydrophilic surface (coded as M-NC) on the receiving side have been designed, developed and evaluated in EMBRs. Compared to commercial polydimethysiloxane (PDMS) tubular membranes, both NC and M-NC possessed 10 times higher phenol extraction efficiency in an aqueous-aqueous extractive membrane process. The uncontrolled biofilm growth on the membrane surface after 12 days of cross flow EMBR (CF-EMBR) operation resulted in 62% reductions of overall mass transfer coefficients (k0) of both NC and M-NC. However, both membranes exhibited better performance in a submerged EMBR (S-EMBR) configuration due to the presence of air bubbles scouring on the membrane surface. Moreover, the fouling-releasing fluoro-polymeric surface of the hydrophobic NC was able to attenuate the tendency of microbial attachment and encourage biofilm scouring from the membrane surface in the S-EMBR. In contrast, more polysaccharides were present in the biofilm on the poly (ethylene glycol) (PEG)-modified M-NC surface, which acted as adhesives to tightly immobilize the biofilm on the membrane surface. Lastly, the NC which exhibited a higher stable k0 of 5.7 × 10−7m/s in 12 days of S-EMBR operation, has been tested in a pilot S-EMBR to treat actual industrial wastewater. It showed a stable and competitive k0 of 6.5 × 10−7m/s in 31 days operation, demonstrating its feasibility for hostile industrial wastewater treatment.

Phenol biodegradation and microbial community dynamics in extractive membrane bioreactor (EMBR) for phenol-laden saline wastewater

An extractive membrane bioreactor (EMBR) for phenol-laden saline wastewater was set up in this study to investigate the variations of phenol removal, extracellular polymeric substance (EPS) release and microbial community dynamics. The gradual release of phenol and the total separation of salt were achieved by silicon rubber tube membrane. Only phenol (55.6–273.9mg/L) was extracted into microorganism unit from wastewaters containing 1.0–5.0g/L phenol and 35.0g/L NaCl. After 82d of EMBR operation, maximal 273.9mg/L of phenol was removed in EMBR. Low concentration of phenol in wastewater (2.5g/L) played a favorable effect on the microbial community structure, community and dynamics. The enumeration of Proteobacteria (30,499 sequences) significantly increased with more released EPS (82.82mg/gSS) to absorb and degrade phenol, compared to the virgin data without phenol addition. However, high concentration of phenol showed adverse effects on EPS release, microbial abundance and biodiversity.

Preparation of Polydimethylsiloxane–Polyvinylidene Fluoride Composite Membranes for Phenol Removal in Extractive Membrane Bioreactor

The extractive membrane bioreactor (EMBR) system combining a membrane process and a biological process has been developed to extract and biodegrade recalcitrant organic pollutants in wastewater. Removal of the organics such as phenol by EMBR requires an effective membrane to selectively extract the organic compounds while rejecting water and other harsh inorganic components. In this work, novel composite membranes consisting of a highly porous substrate, made by tiered polyvinylidene fluoride (PVDF) nanofibers with ultrafine nanofibers on top (61 ± 12 nm in diameter), and a dense polydimethylsiloxane (PDMS) selective layer have been fabricated. We have investigated (1) the effect of the pore size of PVDF nanofibrous substrates, (2) the effect of PDMS preparation method, and (3) the effect of prewetting agent on the resultant composite membranes’ morphologies, mechanical properties, and phenol removal performance. Compared with the symmetric substrate with a nanofiber diameter of 129 ± 13 nm, the tiered su...

Controlling biofilm development in the extractive membrane bioreactor

ABSTRACTThe extractive membrane bioreactor can be used as a treatment of difficult organics in hostile wastewater. In this study, it was applied to phenol-contaminated saline water, where phenol is extracted from the feed stream through a dense membrane to the bioprocess, which is principally a biofilm on the downstream side of the membrane. Our study shows that uncontrolled biofilm growth (after 14 days of crossflow operation) can result in 42% reduction in phenol mass transfer. Biofilm control strategies such as reducing the inorganic loading rate and adopting a submerged aerated configuration to encourage membrane scouring were assessed in this study and limited the phenol mass transfer reduction to 13%.

Composite hollow fiber membranes with different poly(dimethylsiloxane) intrusions into substrate for phenol removal via extractive membrane bioreactor

Due to its toxicity to ecosystem, phenol removal from industrial wastewater before discharge is a priority concern. Extractive membrane bioreactor (EMBR), a novel wastewater treatment process combining aqueous–aqueous extractive membrane process and biodegradation, has shown potential in treating phenol in wastewater. In this paper, composite hollow fiber membranes with different levels of poly(dimethylsiloxane) (PDMS) intrusion were prepared by coating a layer of PDMS on a Polyetherimide (PEI) hollow fiber substrate. Their applicability to EMBR for phenol removal was studied. The prepared membranes were characterized by microscopy and gas permeation test, and their performances were evaluated in aqueous–aqueous extractive membrane processes and EMBR process. The overall mass transfer coefficient for phenol, or k0, was found to be significantly affected by the level of PDMS intrusion in the composite membranes. This is because the penetration of PDMS into the porous substrate results in a denser membrane structure, which consequently increases the membrane resistance. A slight penetration of PDMS into the substrate was found to be necessary for the composite membranes to achieve high k0 while maintaining low inorganic flux across the membranes. Wilson-plot analysis suggests that membrane resistance dominated over liquid boundary layer resistances. After more than 250h of EMBR operation, significant biofilm growth was observed on the composite membranes and the k0 was dropped but stabilized at around 7.5×10−7m/s. This k0 was 7.5 times higher than commercial PDMS tubular membranes (without biofilm development) reported in previous studies, confirming the superiority of thin film composite membranes prepared in this work. It was also found that process optimization to control biofilm thickness is important in order to enhance phenol removal rate in EMBR.

Drinking Water Denitrification Using Membrane-Based Technologies

In many countries, nitrate concentrations in surface and ground water have exceeded the concentrations set by drinking water regulations. Hence, several strategies for management, control and the treatment of drinking water resources have been developed in recent years. Although several physicochemical treatment alternatives are in use, they have high construction and operational costs. Also, the secondary brine or concentrated waste is generated after physicochemical treatment processes. Hence, biological denitrification can be considered as an alternative for drinking water treatment. However, the contamination risk of the drinking water by microorganisms and the organic/inorganic nutrients during the denitrification process is the major concern and the biological treatment of drinking water may attract the negative public reaction. In order to eliminate or minimize the risks, membrane-based biological denitrification technologies, including both autotrophic and heterotrophic processes have been developed for drinking water treatment. In this review, membrane-based bioprocesses have been presented together with their advantages/disadvantages and the selection criteria. In this context, heterotrophic membrane bioreactor (MBR), extractive MBR, hydrogen-based membrane biofilm reactor (MBfR), and the autotrophic sulfur-based MBR processes have been comparatively discussed. Keywords: Autotrophic denitrification, denitrification, drinking water, heterotrophic denitrification, membrane biofilm reactor, membrane bioreactor, sulfur based denitrification.

Novel MBRs for the removal of organic priority pollutants from industrial wastewaters: a review

AbstractOrganic pollutants which are commonly discharged by the 21 industrial groups identified by the US EPA are regulated under the toxic and priority pollutants list. Novel membrane bioreactor (MBR) systems developed in the last two decades, such as the high‐retention MBRs (HR‐MBRs) and extractive MBRs (EMBRs), could be applied in the retention/extraction of targeted organics from point‐source industrial wastewater to meet stringent regulatory requirements. This paper combines previous reviews and studies conducted on the individual novel MBRs to discuss the potential in applying these technologies in the removal of targeted organic pollutants from industrial wastewater by providing a summary of the technologies and discussing the research gaps that currently hamper their commercialization. Future research should focus on long‐term operation with real industrial wastewaters to identify membrane, operational and biodegradation limitations for further optimization. This includes advances in microbiology and the application of novel membranes to boost the biodegradation and removal capabilities of these novel MBR systems. Energy and economic analyses of the MBRs operated at the pilot/demo scale are required to compare their benefits with conventional treatment systems. © 2015 Society of Chemical Industry

Mathematical modeling of a time-dependent extractive membrane bioreactor for denitrification of drinking water

A mathematical model was developed for a two-dimensional transient nitrate transport through an extractive membrane bioreactor (MBR) with a hollow-fiber membrane module which is used in the denitrifying system of drinking water. Denitrification takes place on the shell side of the membranes, creating a driving force for a mass transfer. The presented CFD model formulates and solves the couples of fundamental mass and momentum balance equations using numerical techniques. Simulation results showed that with an increase in feed flow rate, MBR efficiency decreases. Moreover, MBR efficiency increases as the feed concentration rises. In addition, when the effect of membrane structural parameters was investigated; it was shown that the restrictive factor, Kr, has a distinctive effect on MBR efficiency. Besides, using three correlations to estimate the tortuosity as a function of porosity, the effect of porosity was examined and it demonstrated that MBR efficiency was affected by a low value of 2.8% difference in the standard deviations of these three correlations. Finally, the simulation results demonstrate that the model is a good predictive one, especially from the hydrodynamics point of view. Comparing the simulation results with the experimental data, a reasonable conformity with deviations of smaller than 8.00% was achieved.

Biological treatment of toluene contaminated wastewater by Alcaligenese faecalis in an extractive membrane bioreactor; experiments and modeling

Conventional wastewater treatment methods are not efficient in treating wastewaters contaminated with volatile hydrocarbons such as benzene, toluene and xylenes (BTX). The aim of this study is to enhance the efficiency of an extractive membrane bioreactor (EMBR) in treating toluene contaminated wastewater by usage of pure culture of Alcaligenese faecalis. Toluene was used as a model of toxic contaminant because of its wide presence in wastewaters contaminated with petrol derivatives. The Haldane kinetic model adequately described the dynamic behavior of the toluene biodegradation by the strain of A. faecalis over a wide range of initial toluene concentrations (50-1,000 mg L(-1)) with kinetic constants micro(max) = 0.066 h(-1), k(s) = 91.7 mg/L and k(I) = 278.2. Overall mass transfer coefficient has been measured and described as resistance in the series model. No biofilm formed on the exterior surface of the membrane; however in previous works the layer of the biofilm on the exterior surface of the membrane acts as a mass transfer resistance. A mathematical model was developed to predict the pollutant concentration profile along the tube side of the membrane modules.