Feed Flow Velocity Research Articles

Performance of capacitive deionizing membrane distillation (CDIMD) process for the organic sewage treatment and how operating parameters can affect it

To solve the fouling issue of traditional membrane distillation (MD) technique, a newly-designed hybrid purification system integrating capacitive deionization (CDI) with MD technology was established for the organic sewage treatment in this study, namely capacitive deionizing membrane distillation (CDIMD) technology. Complexes formation via cross-linking among protein, divalent cations, and polysaccharide, an archcriminal inducing MD fouling, was remarkably alleviated in the CDIMD system considering that negatively-charged organics were clearly divided away from those divalent cations in an electric field circumstance. The CDIMD performance was deeply explored in this study focusing on the impact mechanisms of core operational parameters. An appropriate increment of feed temperature (60–65 °C) and feed flow velocity (15.72–17.82 mm/s) contributed to the anti-fouling performance of CDIMD. Considering the side reactions at voltage >1.2 v, setting working voltage at around 1.2 v seemed to be optimal for CDIMD operation. With an overall consideration of pure water production and anti-fouling performance, a properly thicker CNTs layer (40–60 μm) efficiently enhanced the fouling mitigation of CDIMD. A frequent switching of electric field direction (9/1 min) facilitated the timely regeneration of electrode and composite membranes, accordingly promoting a reliable purification of organic wastewater by CDIMD technique.

Application of capacitive deionizing membrane distillation (CDIMD) system for seawater desalination: Emphasizing on the impacts of operating parameters

Although membrane distillation (MD) is highly regarded as a promising technique for seawater desalination, membrane scaling induced by the accumulation of crystals is the crucial obstacle for real application of MD. Capacitive deionization (CDI), another novel desalination technology, is mainly applied in the desalination of hyposaline water, and its desalination efficiency is inferior to MD. Even so, the electro-absorption desalination mechanism of CDI is a novel enlightenment for alleviating MD scaling. Hence, we developed a new-type desalination technique by integrating CDI with traditional MD system to retard MD scaling, namely capacitive deionizing membrane distillation (CDIMD) technique. In the CDIMD system, the anions and cations were respectively separated by the activated carbon fiber felt (ACFF) electrodes and lab-made electrically conductive membranes (CNTs-PTFE), accordingly alleviating the combination of salt ions and the subsequent membrane scaling development. The influences of crucial operation parameters of CDIMD on the desalination efficiency were deeply researched. The results revealed that feed temperature of around 65 °C, feed flow velocity of 15.72 mm/s, operating mode of forward-CDIMD, input voltage of 1.2–1.6 v, CNTs thickness of 40–60 μm, and a short time-set of ion-adsorption/desorption phases (9/1 min and 17/3 min) might contribute to the CDIMD desalination.

Electro mitigation of calcium carbonate and calcium sulfate scaling in an optimized thermal conductive membrane distillation process

Desalination technology can obtain fresh water from brine to alleviate the pressure of global water scarcity. Membrane distillation (MD) is a promising technology for desalination, especially for hypersaline brine. Although the emergence of novel processes enhances the competitiveness of MD in desalination, membrane-based separation technology inevitably leads to membrane fouling, thereby decreasing flux and thermal efficiency. Herein, we prepared an electroactive membrane and using it in an optimized thermal conductive membrane distillation process. Optimizing the thermal conducting layer can improve the desalination performance. Aiming to the typical membrane scaling of calcium carbonate and calcium sulfate, we elucidated the influence of the thermal conducting layer temperature, porosity, and feed velocity on the formation of the foulants. Results showed that the increase in porosity of the thermal conducting layer, the decrease in temperature, and the increase in feed flow velocity were conducive to alleviating the scaling of calcium carbonate and calcium sulfate. Regular electro-cleaning effectively alleviated calcium carbonate scaling, whereas continuous application of a potential to the membrane mitigated the calcium sulfate scaling. The mechanism of electrochemical mitigation of calcium carbonate and calcium sulfate scaling included forming an electric double layer, generating electrostatic repulsion to inhibit the formation of crystals, and changing the pH to dissolve the crystals.

Modelling and analysis of hydrodynamics and flow phenomena of fluid with formic acid as pollutant in the reactive area of a flat plate photocatalytic reactor with top and bottom turbulence promote

The inadequate mixing of pollutant and its low mass transfer in the reactive surface reduces the efficiency of photocatalytic reactor. A computational model is developed, and numerical analysis is conducted to examine the effect of top and bottom baffles on the mass transfer and hydrodynamic performance of the reactor compared to reactor without baffle in this study. The hydrodynamic flow phenomena such as local streamlines, velocity, turbulence characteristic, pressure-drops, and wall shear stress were investigated. The experiment was done in a lab-scale flat-plate photocatalytic reactor using Formic Acid as pollutant in feed water for model validation. The FA concentration versus feed flow rate and velocity as a function of time showed good agreement between simulation and experimental results (only about 5 % variation). From the simulation, it was found that the pressure drops increase with increase in baffle height and the lowest was found to be 0.1 kPa and 0.4 kPa when the baffle height was 5 mm at velocity of 0.15 m/s and 0.5 m/s respectively. The highest turbulent kinetic energy and the dissipation was found 0.215 m2/s2 and 46 m2/s3 respectively when the baffle height was 12 mm in the present simulation. Baffles significantly changes the hydrodynamic performance such as turbulence, velocity, mass of pollutant and the pressure drops. The velocity magnitude also increases and the highest was found to be 9.2 times of the free stream velocity when 12 mm top baffle was used. Similar trends were found for bottom baffles. The highest magnitude of turbulent kinetic energy was found to be four times higher than the plain reactor without baffle. Therefore, baffle will significantly promote turbulence and improve the hydrodynamic performance thus enhance the photocatalytic rector performance.

Microflow precipitation of barium sulfate nanoparticles from mineral barium sulfide black ash

Microflow precipitation reaction is an effectively method for preparing high quality nanoparticles. In this study, BaSO4 nanoparticles were successfully prepared from BaS black ash in a simple capillary microreactor. Two important microflow parameters, feed flow velocity and residence time, on morphology, structure, component, average particle size (dav) and coefficient of variation (CV) of the as-synthesized product are investigated. The results show that well-dispersed ellipsoidal nanoparticles of BaSO4 with purity >99 wt% can be prepared using this novel method. High flow velocity is beneficial for producing small particles with low CV, and short residence time is also good for slightly small particles but with high CV. The dav and CV values are in the range of 33.8∼53.5 nm and 0.32∼0.39, respectively. In addition, the preparation of the BaSO4 product by this new method is compared with those by precipitation in other typical reactors. Combined with the simplicity of the microchannel structure, continuity of process operation and atomic economy of the raw materials, this proposed method is effective for preparing high quality BaSO4 nanoparticles with narrow particle size distribution.

Numerical Study of the Flow of Pollutants during Air Purification, Taking into Account the Use of Eco-Friendly Material for the Filter—Mycelium

To improve air quality, it is customary to apply technological measures to isolate or retain pollutants by influencing the polluted stream in various ways to effectively remove the pollutants. One of the most commonly used measures is a filter, in which the air flow passes through a porous aggregate. A variety of filter materials allows very selective and precise cleaning of the air flow in non-standard or even aggressive microclimate conditions. In this paper, the environmental aspect of the used materials is discussed, and a theoretical model of an adapted mycelium is proposed as an alternative to the use of filter materials to predict air flow purification. In the created numerical model of an idealized filter, several cases are considered when the pore size of the mycelial fillers reaches 1.0, 0.5 and 0.1 mm, and the feed flow velocity reaches 1–5 m/s. Moreover, in the mycelium itself, the flow velocity can decrease and approach the wall to a value of 0.3 m/s, which is estimated for additional numerical studies of interaction with the surface. These preliminary studies are aimed at establishing indicative theoretical parameters for favorable air flow movement in the structure of the mycelium.

Performance analyses on a novel evacuated U-tube solar collector powered direct contact membrane distillation hybrid system for seawater desalination

Short lifespan and low thermal efficiency are two key hindering factors for the development of solar desalination system. Herein, a novel hybrid system model of a direct contact membrane distillation (DCMD) desalination system powered by a durable and efficient evacuated U-tube solar collector (EUSC) is proposed. The models of both EUSC and DCMD are mathematically formulated and validated. The permeate flux, energy efficiency and exergy efficiency of the proposed system are deduced as performance indicators. The performance of the proposed system is predicted under the weather conditions of Ningbo city, China. Under the typical weather condition, the maximum permeate flux, energy efficiency and exergy efficiency of the proposed system are 4.45kgm- 2h- 1, 25.47 % and 4.73 %, respectively. The freshwater yields of August and total year of 2021 in Ningbo city, China are presented. Additionally, the long-term performance with past 41 years is also studied. The effects of solar irradiance, environment temperature, feed flow velocity, feed water Reynold number, permeate liquid temperature, permeate flow velocity, porosity and average pore radius of DCMD membrane are investigated via parametric studies. The proposed EUSC/DCMD coupling system may provide a promising alternative to stand-alone, small-scale desalination systems for freshwater generation.

Treatment of 2-Mercapto-5-methyl-1,3,4-thiadiazole (MMTD) wastewater by bipolar membrane electrodialysis: MMTD migration, process factors and implications

2-Mercapto-5-methyl-1,3,4-thiadiazole (MMTD), an important intermediate of widely used cefazolin and cefazedone antibiotics, was hardly decyclized during conventional wastewater treatment, raising a great risk to the environment. In this study, a new strategy for treating MMTD wastewater at the source by bipolar membrane electrodialysis (BMED) was proposed, realizing a material closed loop in the processes of MMTD production. Meanwhile, a laboratory-scale BMED system was set up for exploring MMTD migration, process factors, and technology implications. The results revealed that MMTD in the feed compartment may migrate into the acid/base compartment by electromigration and diffusion, the electromigration process of MMTD microspecies was controlled by its ionization, and the diffusion process of MMTD microspecies was influenced by its chemical potential on both sides of the membranes and the types of membranes. The analysis of the BMED process factors showed that these factors such as the initial pH of the feed solution, current density, flow velocity, and initial acid/base concentration affected the acid/base concentration, MMTD leakage, current efficiency, energy consumption, electric field intensity, ion flux, electrical resistance, head loss, and proton leakage. Based on these effects of the BMED process factors, some new strategies were proposed to optimize BMED process. Besides, the implications of BMED technology were affirmed by surveying the feasibility of BMED product recycling. Furthermore, this type of new strategy could be applied to the treatment of other similar wastewater at the source, realizing a closed loop in its production.

Analytical and numerical investigations of mixing fluids in microchannel systems of different geometrical configurations

AbstractThis work presents theoretical and numerical studies related to micromixing phenomena using two different shapes of microchannel systems (i.e., X‐ and Y‐shaped, respectively). In this study, we consider a system that consists of a primary fluid, an aqueous phase (Fluid A), and a secondary fluid (distributed phase), Rhodamine B, in water (Fluid B). In this study, a two‐dimensional closed‐form generalized analytical model is developed and solved using the method of separation variables to understand the fluid flow mixing behaviour under the influence of a convective–diffusive mass transport process. In addition, numerical simulations are also performed by solving the continuity, momentum, and mass transport equations for the two proposed microchannel systems under different flow conditions to understand the relative effects on micromixing phenomena resulting from the convection and diffusion mass transport. Results obtained from the numerical simulations evaluate the mixing performance by varying the inlet flow velocity of the secondary fluid stream (Fluid B: Rhodamine B in water). The numerical result in terms of the radial concentration distribution profile as a function of channel width based on the operating Reynolds number by varying inlet feed flow velocity (Fluid B) shows that more effective mixing has been carried out by the X‐shaped microchannel compared to the Y‐shaped microchannel. Moreover, the proposed generalized analytical model was validated with the obtained numerical results in terms of the normalized concentration distribution as a function of the normalized channel width. A good agreement between the analytical and obtained numerical results ( for both shapes of microchannel systems has been observed.

3D CFD study and optimisation of static mixer type feed spacer for reverse osmosis

Innovative designs of feed spacers for various applications of membrane-based separation processes are required to be identified. We proposed the static mixer type flat sheet of feed spacer and studied the shear stress and mass transfer around it in the flow channel. The enhanced mass transfer could be obtained by increasing the feed flow velocity at the expense of increased pressure drop. Box-Behnken design (BBD) of response surface methodology (RSM) along with desirability function analysis was used for the optimisation of the geometry with the average mass transfer at the membrane surfaces, pressure drop along the flow direction and channel Reynolds number as the optimisation parameters. The optimum geometry found corresponds to (lh) = 0.5 and θ = 45° at the channel Reynolds number of 78. The spacer configuration efficacy of the optimised geometry was found to be 20.7 × 10−6, which is in line with the reported data. However, the variation in the values of the average Sherwood number with the power number is slower than the commercial as well as other state-of-the-art geometries reported, opening up an opportunity to operate the system at lower Re, thereby increasing the permeate recovery at the same operating pressure.

Separation of Drugs by Commercial Nanofiltration Membranes and Their Modelling.

Pharmaceutical drugs have recently emerged as one the foremost water pollutants in the environment, triggering a severe threat to living species. With their complex chemical nature and the intricacy involved in the removal process in mind, the present work investigates the performance of commercially available polyamide thin-film composite tubular nanofiltration (NF) membranes (AFC 40 and AFC 80) in removing polluting pharmaceutical drugs, namely caffeine, paracetamol and naproxen. The structural parameters of the NF membranes were estimated by water permeability measurements and retention measurements with aqueous solutions of organic, uncharged (glycerol) solutes. The effect of various operating conditions on the retention of solutes by the AFC 40 and AFC 80 membranes, such as applied transmembrane pressure, tangential feed flow velocity, feed solution concentration and ionic strength, were evaluated. It was found that the rejection of drugs was directly proportional to transmembrane pressure and feed flow rate. Due to the size difference between caffeine (MW = 194.9 g/mol), naproxen (MW = 230.2 g/mol) and paracetamol (MW = 151.16 g/mol), the AFC 40 membrane proved to be efficient for caffeine and naproxen, with rejection efficiencies of 88% and 99%, respectively. In contrast, the AFC 80 membrane proved to be better for paracetamol, with a rejection efficiency of 96% (and rejection efficiency of 100% for caffeine and naproxen). It was also observed that the rejection efficiency of the AFC 80 membrane did not change with changes in external operating conditions compared to the AFC 40 membrane. The membrane performance was predicted using the Spiegler–Kedem model based on irreversible thermodynamics, which was successfully used to explain the transport mechanism of solutes through the AFC 40 and AFC 80 membranes in the NF process.

The Impact of Operational Parameters on Polypropylene Membrane Performance during the Separation of Oily Saline Wastewaters by the Membrane Distillation Process

In the present study, membrane distillation (MD) was applied for the treatment of oily saline wastewaters produced on ships sailing the Baltic Sea. For comparison purposes, experiments were also carried out with model NaCl solutions, the Baltic Seawater and oil in water emulsions. The commercial Accurel PP V8/2 membranes (Membrana GmbH, Germany) were used. In order to investigate the impact of the operational parameters on the process performance, the experiments were conducted under various values of the feed flow velocity (from 0.03 to 0.12 m/s) and the feed temperature (from 323 to 343 K). The obtained results highlight the potential of PP membranes application for a stable and reliable long-term treatment of oily wastewater. It was demonstrated that the permeate flux increased significantly with increasing feed temperature. However, the lower temperature ensured the limited scaling phenomenon during the treatment of oily wastewaters. Likewise, increasing the feed flow velocity was beneficial to the increase in the flux. Moreover, it was found that performing a cyclic rinsing of the module with a 3% HCl solution is an effective method to maintain a satisfactory module performance. The present study sheds light on improving the MD for the treatment of oily wastewaters.

Conductive Fe3O4/PANI@PTFE membrane for high thermal efficiency in interfacial induction heating membrane distillation

Conventional membrane distillation (MD) undergoes interfacial temperature polarization and thus may suffer from a reduced thermal efficiency when using the hot saline water as the primary thermal driver. To address this issue, this study employed a conductive Fe3O4/polyaniline (PANI) coated polytetrafluoroethylene (Fe3O4/[email protected]) membrane to achieve local interfacial heating under electromagnetic induction and promote the thermal efficiency of direct-contact MD (DCMD). Induction-responsive Fe3O4 nanoparticles were dispersed in a conductive PANI polymer matrix that binds to the hydrophobic porous PTFE membrane by spray coating. Dispersing Fe3O4 nanoparticles in a conductive PANI polymer matrix doubled the heating efficiency (2.0 °C s−1) than directly dispersing Fe3O4 nanoparticles onto PTFE without PANI (1.1 °C s−1). This enhanced heating efficiency is ascribed to the formation of multiple conductive pathways or eddy current channels via the conductive polymer networks. A parametric study of the DCMD performance revealed that the permeate flux increased from 0.7 to 3.4 L m−2 h−1 with the increase of the coolant flow velocity (1.4–22.9 cm min−1) and induction power (0.9–3.6 kW). However, increasing the feed (3.5 wt% NaCl solution) flow velocity (1.4–8.6 cm min−1) significantly reduced the permeate flux from 5.0 to 1.6 L m−2 h−1 due to the insufficient time of water/membrane contact for mass transfer. Moreover, thermal and mass transport processes at the induction-heated membrane interface were analyzed by finite element analysis (FEA), which matched well the experimental results and determined the thermal efficiency up to 88% as opposed to the reported levels (20–58%) for the conventional DCMD. Our study laid additional foundation for induction-heating DCMD by devising new composite membrane materials and new interfacial thermal and mass transfer mechanisms.

Direct contact membrane distillation (DCMD) process for simulated brackish water treatment: An especial emphasis on impacts of antiscalants

Membrane distillation (MD) has been considered as a promising technique for brackish water desalination, while the membrane fouling issue, especially the membrane scaling, have been the main obstacle for the widespread application of MD system. Antiscalant, as an economical tool for scaling control, has been widely applied to other membrane separation processes, like RO and UF. Therefore, three types of typical antiscalants, including PBTCA, DTPMPA, and HPMA, were applied in this work to investigate their anti-scaling performances during the MD desalination of brackish water. Additionally, the impacts of antiscalants on fouling layer development as well as the desalination efficiency of MD system were also deeply researched in this study. Compared to DTPMPA, PBTCA and HPMA performed better scaling inhibition in MD system, resulting in remarkable mitigation of flux decline. With the usage of PBTCA, these mineral substances were largely distributed in feed solutions with the dissolved state, partly facilitating the biofilm formation. Differently, these salts mainly existed in the form of distorted slags with the presence of HPMA, and the biofilm development was notably retarded by the deposited slags. These loose slags could be easily removed from the MD membrane by increasing the feed flow velocity, thus it can be summarized that HPMA was more suitable for the long-period MD desalination of brackish water. The application of DTPMPA should be strictly restricted in MD desalination units considering the risk of pore wetting.

Seawater Desalination Based on a Bubbling and Vacuum-Enhanced Direct Contact Membrane Distillation

A Bubbling and Vacuum-enhanced direct contact membrane distillation (BVDCMD) is proposed to improve the water production rate of the direct contact membrane distillation (DCMD-)based seawater desalination process. Its heat and mass transfer mechanism are theoretically analyzed, and a CFD model is established, which is verified by the published data. Four types of the noncondensable gas, “O2,” “air,” “N2,” and “H2,” are adopted as the bubbling gas, and their process enhancements under different pressure of permeate side, temperature, and NaCl concentration of feed side and flow velocities are investigated. The results show that the permeate flux increased remarkably with the decrease in the viscosity of the bubbling gas, and hence, “H2” is the best option for the bubbling gas, with the permeate flux being enhanced by 144.11% and the effective heat consumption being increased by 20.81% on average. The effective water production rate of BVDCMD is predicted to be 42.38% more than that of DCMD, proving its feasibility in the seawater desalination.

Membrane fouling in direct contact membrane distillation for liquid desiccant regeneration: Effects of feed temperature and flow velocity

Membrane fouling is a major challenge of membrane distillation when employed as a regenerator in liquid desiccant air-conditioning systems. The present work investigated the impacts of feed temperature and flow velocity on the occurrence of membrane fouling using a bench-scale direct contact membrane distillation (DCMD) system to regenerate a 27.5 wt% of lithium chloride (LiCl) solution. The membranes used at different operating conditions were characterized and compared by scanning electron microscopy and water contact angle measurement. The results showed that increasing feed inlet temperature significantly improved the DCMD regeneration capacity but reduced the membrane hydrophobicity. The DCMD operated at a higher cross flow velocity exhibited a higher propensity of membrane fouling. Membrane fouling tended to accumulate from loose LiCl crystals to a dense scaling layer with an increase in both feed inlet temperature and cross flow velocity. Membrane cleaning with deionized water was an effective mitigation strategy to remove the LiCl deposition from the membrane surface. It can effectively restore the DCMD regeneration performance and increase the hydrophobicity of the fouled membrane by 10.6%. However, using the post-cleaning membrane increased the risk of membrane wetting in the DCMD regeneration process.

Decontamination of uranium contained low-level radioactive wastewater from UO2 fuel element industry with vacuum membrane distillation

The rapid development of nuclear industry has generated large quantities of low-level radioactive wastewater (LLRW) to pose a potential threat globally. In this study, the feasibility of vacuum membrane distillation (VMD) process for the decontamination of uranium contained LLRW from UO2 fuel element production has been studied using commercial PTFE hollow fiber membrane. The effects of operation conditions, such as feed temperature/pH, vacuum pressure and feed flow velocity were investigated and optimized with artificial UO2(NO3)2 solution. The real process wastewater from the UO2 fuel element factory were then treated by VMD process under the optimized conditions for 1400 min with the concentration factor up to 9. No clear evidence of membrane fouling or wetting were noticed during the VMD operation nor the membrane autopsy studies. With an average permeate flux of 7.3 L m−2 h−1, it exhibited excellent retention towards all major contaminates such as uranium, COD, and NH4+-N to meet the Integrated Wastewater Discharge Standard of China (GB 8978-1996) for direct discharge.

Textile dye wastewater treatment by direct contact membrane distillation: Membrane performance and detailed fouling analysis

The treatment of textile dye solution is considered one of the most challenging wastewater treatments, representing a major concern for the ecosystem. This study investigates the efficiency of direct contact membrane distillation (DCMD) for the treatment of synthetic textile solution in lab test membrane cells. The effect of the feed temperature and feed flow rate on the MD fouling were investigated at feed water temperatures of 40 °C, 60 °C, 80 °C and feed flow rates of 15 L/h, 30 L/h and 45 L/h. Results show that (i) negligible fouling was observed at a feed temperature of 40 °C, (ii) the increase in temperature impacted the process performance, leading to severe flux decrease (~70%) and to the formation of a thick fouling layer (240 μm) at a feed temperature of 80 °C, (iii) fouling thickness was reduced with increasing feed flow velocity, (iv) the fouling increased toward the inlet side of the membrane cell due to the variation of the driving force along the module. In-situ non-invasive fouling monitoring allowed evaluating the fouling spatial distribution on the membrane, and linking the MD process performance to the fouling accumulation, indicating a linear correlation between the flux decrease and the fouling deposition.

Integration of Forward Osmosis Membrane Bioreactor (FO-MBR) and Membrane Distillation (MD) units for water reclamation and regeneration of draw solutions

In the current lab scale study, the two treatment technologies of FO (Forward osmosis) and DCMD (Direct contact membrane distillation) were used in combination to create a continuous treatment system for water reclamation using, inorganic NaCl, surfactant (Tetraethyl ammonium bromide, TEAB) and polyelectrolyte (Polydiallyldimethylammonium chloride, PDAC) as FO draw solutes with both DI water (FO-MD), and monoculture municipal synthetic wastewater with Bacillus subtillis inoculum as feed (FOMBR-MD).Each of the units was optimized separately at bench scale, and then combined to form a Forward Osmosis Membrane Bioreactor – Membrane Distillation (FOMBR-MD) hybrid for water reclamation from wastewater. In this hybrid system, the diluted draw solution was fed to the MD unit for reconcentration. The MD unit was tested at various operating temperatures; for FO-MD, a temperature difference of 15 °C was chosen, with a feed temperature of 35 °C and a permeate temperature of 20 °C. For the FOMBR, the temperature difference was increased to 25 °C. When the cross flow velocity was kept constant, the MD flux increased significantly with increasing temperature. Low grade waste heat from industry can potentially be utilised for the FO-MD process. The increase in flux was higher for NaCl and TEAB (60–80 %) when compared to PDAC (20–50 %), as the temperature difference increased to 35 °C. A greater feed flow velocity increased the turbulence in the flow channel, and increased the MD flux. Up to a 60 % increase in flux was observed when the feed velocity was increased from 0.12 to 0.17 m/s, while the increase in flux was not as high when the flow was increased from 0.17 to 0.21 m/s and thus 0.17 m/s was chosen as the cross- flow velocity for MD. Higher feed concentrations tended to reduce vapour pressures and hence decreased the MD water fluxes.The flux for FO-MBR and MD were well balanced for lower molecular weight draw solutes, but lower FO fluxes were observed for higher molecular weight draw solutes (TEAB, PDAC). This greater imbalance reflected their lower diffusivities and greater tendencies toward concentration polarization. Reverse solute transport (RST) values leading to salinity or toxicity were not reflected by the observations, and therefore it was feasible to run an FOMBR-MD Hybrid for extended times. However, a greater decline in flux versus time was observed for NaCl than for TEAB. PDAC showed the lowest but most stable flux, and a lesser fouling tendency compared to that of TEAB. Overall, The FO-MD hybrid enabled pure water production and a non-volatile component rejection of nearly 99 %, with an RST of <0.1 GMH for the draw solutions back to the FO feed and a much lower solute transport from the MD feed to the permeate. NaCl and other low molecular weight solutes are recommended when high fluxes and system stability are priorities and where high reverse solute transport (RST), leading to salinity or solute toxicity in the MBR feed tank, is not an issue. Higher molecular weight solutes, such as TEAB or PDAC, are recommended when high flux is less critical and when the sensitivity of the microbial consortium to RST and solute toxicity is a concern. In all cases, some degree of process control is recommended in order to bring the systems more quickly to a stable operating state; periodic membrane cleaning is deemed necessary to maintain this state.

Comparison of Polypropylene and Ceramic Microfiltration Membranes Applied for Separation of 1,3-PD Fermentation Broths and Saccharomyces cerevisiae Yeast Suspensions.

In recent years, microfiltration (MF) has gained great interest as an excellent technique for clarification of biological suspensions. This paper addresses a direct comparison of efficiency, performance and susceptibility to cleaning of the ceramic and polymeric MF membranes applied for purification of 1,3-propanediol (1,3-PD) fermentation broths and suspensions of yeast Saccharomyces cerevisiae. For this purpose, ceramic, titanium dioxide (TiO2) based membranes and polypropylene (PP) membranes were used. It has been found that both TiO2 and PP membranes provide sterile permeate during filtration of 1,3-PD broths. However, the ceramic membrane, due to the smaller pore diameter, allowed obtaining a better quality permeate. All the membranes used were highly susceptible to fouling with the components of the clarified broths and yeast suspensions. The significant impact of the feed flow velocity and fermentation broth composition on the relative permeate flux has been demonstrated. Suitable cleaning agents with selected concentration and duration of action effectively cleaned the ceramic membrane. In turn, the use of aggressive cleaning solutions led to degradation of the PP membranes matrix. Findings of this study add to a growing body of literature on the use of ceramic and polypropylene MF membranes for the clarification of biological suspensions.