Conventional Membrane Processes Research Articles

Dual-stage forward osmosis/pressure retarded osmosis process for hypersaline solutions and fracking wastewater treatment

Hypersaline solution with high TDS is not suitable for direct treatment by the conventional membrane and thermal processes. The current study proposes a dual-stage FO/PRO process for hypersaline solution treatment and power generation. The treatment process reduces the concentration of saline wastewater and hence renders it suitable for disposal directly to sea or treatment by the conventional membrane and thermal processes. The draw and feed solutions in the FO process were the hypersaline solutions and wastewater effluent, respectively. Five concentrations were evaluated for the process treatment with different concentrations ranging from 53g/L to 157g/L. The performance of FO membrane was estimated using pre-developed computer software. The results showed that a higher power can be generated from the PRO-FO system than from the FO-PRO system without compromising the concentration of hypersaline solution after dilution. The study also showed that although increasing the flow rate of draw solution resulted in an increase in the permeate flow rate, it caused a reduction in the dilution of draw solution. On the other hand, the study showed a negligible improvement in the performance of FO membrane upon increasing the feed solution flow rate. Finally, the simulation results showed that the concentration of diluted draw solution was suitable for the conventional membrane and thermal treatments or discharge to seawater after the dual-stage FO membrane treatment.

Impact of spacer thickness on biofouling in forward osmosis

Forward osmosis (FO) indirect desalination systems integrate wastewater recovery with seawater desalination. Niche applications for FO systems have been reported recently, due to the demonstrated advantages compared to conventional high-pressure membrane processes such as nanofiltration (NF) and reverse osmosis (RO). Among them, wastewater recovery has been identified to be particularly suitable for practical applications. However, biofouling in FO membranes has rarely been studied in applications involving wastewater effluents. Feed spacers separating the membrane sheets in cross-flow systems play an important role in biofilm formation. The objective of this study was to determine the influence of feed spacer thickness (28, 31 and 46 mil) on biofouling development and membrane performance in a FO system, using identical cross-flow cells in parallel studies. Flux development, biomass accumulation, fouling localization and composition were determined and analyzed. For all spacer thicknesses, operated at the same feed flow and the same run time, the same amount of biomass was found, while the flux reduction decreased with thicker spacers. These observations are in good agreement with biofouling studies for RO systems, considering the key differences between FO and RO. Our findings contradict previous cross-flow studies on particulate/colloidal fouling, where higher cross-flow velocities improved system performance. Thicker spacers reduced the impact of biofouling on FO membrane flux.

A pulse electrochemical deposition method to prepare membrane electrode assemblies with ultra-low anode Pt loadings through in situ construction of active core–shell nanoparticles on an electrode

Ultra-low Pt loading membrane electrode assemblies (ULP MEAs) are prepared through in situ construction of core–shell Ir@Pt nanoparticles (Ir/Vulcan XC-72R as the core) on the surface of an electrode via a pulse electrochemical deposition (PED) approach. The core material is coated on a membrane with a conventional catalyst-coated membrane process prior to the deposition of the shell metal (Pt in this case). The ULP MEAs are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The effects of a number of preparation parameters on cell performance are investigated in detail. The performance of the ULP MEA, in which the anode loadings of Pt and metals are ∼0.012 mg cm−2 and 0.044 mg cm−2(0.012 mg cm−2 Pt + 0.032 mg cm−2 Ir) respectively, is found to be competitive with that of an MEA prepared with an anode Pt loading of 0.1 mg cm−2 (commercial Pt/C catalyst from Johnson Matthey), manifesting the solid advantage of this in situ PED method.

Influence of Organic Matters on Forward Osmosis Membrane Performance

Forward osmosis is an emerging membrane technology with potential applications in desalination and wastewater reclamation, osmotic pressure gradient cross the FO membrane is used to generate water flux. In contrast with conventional pressure-driving membrane process, the advantage of FO is significant: energy saving, high solute rejection and low fouling propensity. In this study, alginic acid (AA), boving serum albumin (BSA), humic acid (HA) and tannic acid (TA) were used to investigate the influence of organic fouling. The flux changed obviously, the rejection was approving and the absorption of organics was observed in the study. Ultrasonic oscillation was employed to wipe the organics off the fouling membranes, which was intend to study the quality of absorption of organic matters.

Continuous production and recovery of itaconic acid in a membrane bioreactor

This study presents the fermentative production of the platform chemical itaconic acid using the fungus Ustilago maydis. The innovative aspect here is that the fermentation is run continuously with integrated cell retention and product recovery using membranes. Unlike conventional membrane processes, we use the recently introduced "reverse-flow diafiltration" which prevents performance loss by periodically reversing the flow direction. Results show that filtration stability can be (1) significantly improved compared to conventional membrane processes and (2) product recovery was constantly high at highly dynamic conditions. This is especially remarkable when taking into account the complex nature of fungi cells which tend to block surfaces rapidly.

Selective Separation of Similarly Sized Proteins with Tunable Nanoporous Block Copolymer Membranes

An integral asymmetric membrane was fabricated in a fast and one-step process by combining the self-assembly of an amphiphilic block copolymer (PS-b-P4VP) with nonsolvent-induced phase separation. The structure was found to be composed of a thin layer of densely packed highly ordered cylindrical channels with uniform pore sizes perpendicular to the surface on top of a nonordered sponge-like layer. The as-assembled membrane obtained a water flux of more than 3200 L m(-2) h(-1) bar(-1), which was at least an order of magnitude higher than the water fluxes of commercially available membranes with comparable pore sizes, making this membrane particularly well suited to size-selective and charge-based separation of biomolecules. To test the performance of the membrane, we conducted diffusion experiments at the physiological pH of 7.4 using bovine serum albumin (BSA) and globulin-γ, two proteins with different diameters but too close in size (2-fold difference in molecular mass) to be efficiently separated via conventional dialysis membrane processes. The diffusion rate differed by a factor of 87, the highest value reported to date. We also analyzed charge-based diffusive transport and separation of two proteins of similar molecular weight (BSA and bovine hemoglobin (BHb)) through the membrane as a function of external pH. The membrane achieved a selectivity of about 10 at pH 4.7, the isoelectric point (pI) of BSA. We then positively charged the membrane to improve the separation selectivity. With the modified membrane BSA was completely blocked when the pH was 7.0, the pI of BHb, while BHb was completely blocked at pH 4.7. Our results demonstrate the potential of our asymmetric membrane to efficiently separate biological substances/pharmaceuticals in bioscience, biotechnology, and biomedicine applications.

A review of draw solutes in forward osmosis process and their use in modern applications

Forward osmosis (FO) is one of the emerging membrane technologies which has gained renewed interest recently as a low energy desalination process. The central to FO process is the draw solution (DS) and the membrane because both play a substantial role on its performance. Hence, the selection of an appropriate DS is crucial for the process efficiency. Many DS have been tested so far for a wide range of modern applications and this paper aims to review the various aspects of the DS in the process performance and provides valuable information regarding the selection criteria of suitable DS. Several general DS properties such as the osmotic pressure and the water solubility can affect the process performance. Other intrinsic properties to specific novel DS such as the emerging magnetic nanoparticles (MNPs) can also have an impact on the process efficiency and have to be evaluated. Separation and recovery of the DS are one of the major challenges facing the development of FO process. The recovery process should not be energy intensive, otherwise the FO process cannot be comparable with other pressure-driven processes. Thermolytic solutions such as ammonia carbonates are considered as the promising DS for desalination applications; however, their recovery process efficiency relies on the availability of low-grade heat. MNPs are emerging and effective DS for desalination and can be readily recovered by a magnetic field or conventional membrane processes. However, the aggregation of MNPs due to their magnetic properties has been issued. The vast numbers of studies on the use of NaCl as DS for the treatment of impaired water open up the possibilities of using seawater or reverse osmosis brine streams as suitable DS for such purpose. Fertilisers were also suggested as DS for seawater and wastewater treatment when the diluted DS can be used directly for irrigation. The development of an adequate and efficient DS coupled with a low-cost energy recovery system is crucial to the performance of the process and to achieve success for the large scale of FO.

Development of a simulation program for the forward osmosis and reverse osmosis process

Forward osmosis (FO) is an osmotic process that uses a semi-permeable membrane to effect separation of water from dissolved solutes by an osmotic pressure gradient. Unlike RO, FO does not require high pressure for separation, allowing low energy consumption to produce water. Therefore FO, a potential alternative to conventional membrane process, has been considered a novel technology for seawater desalination. There is no forward osmosis (FO) process simulation program yet, though. Therefore, the main objective of this paper is to develop such computer program based on the solution-diffusion model modified with the film theory for simulating and optimizing the FO, RO, and FO-RO hybrid process. The effect of concentration polarization on FO and RO process efficiency was also considered in the model. A MATLAB-based graphical user interface (GUI) program was used to develop the simulation program. Using the program, the effects of various factors, including the draw solution concentration, feed concentration...

Organic fouling of forward osmosis membranes: Fouling reversibility and cleaning without chemical reagents

The recently resurgent forward osmosis (FO) membrane process has the potential to become a sustainable alternative to conventional membrane processes. However, the fouling and cleaning behavior of FO membranes remains largely unknown. There is a need to fully understand the fouling phenomena in FO in order to take advantage of this emerging technology. In this study, we used alginate as a model organic foulant to examine FO membrane fouling and cleaning behavior with the ultimate goal of determining the underlying FO fouling/cleaning mechanisms. Results showed that alginate fouling in FO is almost fully reversible, with more than 98% recovery of permeate water flux possible after a simple water rinse without any chemical cleaning reagents. We also studied the role of applied hydraulic pressure in membrane fouling and cleaning by performing fouling tests in FO (without hydraulic pressure) and RO (with hydraulic pressure) modes. Flux recovery in the FO mode was much higher than that in the RO mode under similar cleaning conditions, although the rate of membrane flux decline was similar in the two modes. The fouling reversibility of FO was attributed to the less compact organic fouling layer formed in FO mode due to the lack of hydraulic pressure. Our results suggest that operating in FO mode may offer an unprecedented advantage in reducing or even eliminating the need for chemical cleaning. AFM force measurements were used to elucidate the impact of membrane materials (cellulose acetate versus polyamide) on membrane fouling and cleaning behavior. Adhesion force data revealed that a small percentage of relatively adhesive sites on the membrane surface play an important role in increasing membrane fouling potential and decreasing cleaning efficiency. This finding implies that using average adhesion force to predict membrane fouling potential is inadequate. Extensive long-range adhesion forces are observed for the polyamide membrane in the presence of alginate and calcium ions. The long-range interactions are attributed to calcium bridging of alginate molecules between the AFM probe and the adhesive sites on the polyamide membrane surface.

Membrane process opportunities and challenges in the bioethanol industry

Increasing oil prices and growing environmental concerns in recent years have driven the development of renewable biofuels. Until now, most of the bioethanol production concepts are based on sugar and starch crops as feedstock, while research on second generation of bioethanol concepts is investigating the use of cellulosic biomass such as straw, wood, etc. as feedstock. The first part of the paper will review membrane opportunities in the present bioethanol production concepts, while the second part will provide an outlook on the future potentials of membrane technologies in the second generation concepts. For both production concepts, application opportunities for conventional membrane processes such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) as well as the emerging membrane processes pervaporation (PV) and vapour permeation (VP) will be presented. Overall, this paper demonstrates that membrane technology as a highly selective and energy-saving unit operation has a great potential in the bioethanol industry of today and in future. Hence, membrane technology will contribute to solving future energy and environmental problems.

A hybrid microfiltration–granular activated carbon system for water purification and wastewater reclamation/reuse

Microfiltration (MF) does not remove color, natural organic matter (NOM) or synthetic organic chemicals (SOCs). It must be combined with other conventional technologies such as activated carbon adsorption to overcome some of these limitations. The effects of granular activated carbon (GAC) addition on MF performance in terms of quality (dissolved organic carbon) and quantity (permeate flux) were investigated. For a water purification experiment, MF showed preferential rejection of UV 260 (about 30%) compared to dissolved organic carbon (DOC) (about 10%), indicating that the hydrophobic (aromatic) NOM fraction is more efficiently eliminated. In the hybrid MF membrane system, the removal efficiency of UV 260 was about 60% compared to 30% by MF alone, and the decreasing rate of membrane permeability was much less than that of a conventional MF membrane process (about 70 days without GAC and 130 days with GAC). This may result from the reduced organic loading to the membrane due to the adsorption of NOM on the GAC. Using MF alone, the average removal efficiency of specific UV absorbance (SUVA, UV 260/DOC) was only 20%, but GAC addition increased SUVA removal efficiency up to 50–60%. In conclusion, the addition of GAC resulted in a decrease of hydrophobic NOM and trihalomethane precursors. For the wastewater reclamation/reuse experiment, removal efficiencies of DOC, chemical oxygen demand, total nitrogen, total phosphorus and turbidity were in the range of 42%, 53%, 15%, 13%, and 100% with the MF–GAC hybrid membrane system whereas 25–30%, 20–25%, 5–10%, 5–8% and 100% with the MF membrane alone, respectively. The hybrid process of membrane filtration and GAC was more effective in treatment efficiency than the single process.

Photovoltaic powered water purification — challenges and opportunities

One third of the world population does not have access to clean water sources and most of these people are not connected to the electrical grid at the same time. Therefore, photovoltaic (PV) powered water purification suggests itself to be one of the solutions in areas with high sun radiation like India or the MENA (Middle East and North Africa) region. Furthermore, the environmental impact of the process can be reduced substantially as no fuel supply is required. The paper presents a concept of combining a membrane filtration plant with PV power supply only. As PV is a fluctuating energy source and the conventional membrane process needs a constant power input to maintain pressure and flow on the membranes to guarantee their lifetime, some challenges in the system design need to be addressed. Mere coupling of off-the-shelf components does not do the job. A full-scale system for sustainable water purification has been designed and tested in the lab and a pilot location. The results are presented in the paper. Beyond the environmental benefits, the system also competes with standard systems on the market. Based on the experimental results, a cost model has been derived, the main cost factors for the system will be established and a design strategy for a small-scale PV powered system, able to supply a farm or village with safe potable water, is presented.

Elimination of steroidal sex hormones by conventional water treatment and membrane processes

According to date from the literature, steroidal sex hormones are present in water environments in very low concentrations, about 1 ng/l (yet for organisms they are physiologically active). Estradiol and ethinylestradiol were also found in drinking water samples at concentrations of up to 2.1 ng/l and 0.5 ng/l, respectively. Consequently, producing drinking water from hormone-contaminated surface water calls for processes that completely remove these compounds. Therefore, there is a need to develop a method for hormone removal to reduce risk to both humans and the environment. Nanofiltration (NF) is a promising membrane technique with a large number of applications in the field of process water, drinking water or wastewater treatment. NF membranes can separate small organic micropollutants and multivalent ions from liquid streams. Previously the rejection properties of NF membranes for THMs, PAHs and phthalates were examined, and it was found that higher desalting membranes can effectively reject many hazardous organic pollutants. This paper discusses elimination of natural and synthetic steroidal sex hormones by conventional water treatment and membrane techniques from the aqueous phase. The efficiency of coagulation and adsorption on a granulated activated carbon process were not good enough to remove these compounds completely from water. As a second stage of water treatment, NF and coagulation–NF integrated systems were proposed. The application of NF in the second step of water treatment made it possible to remove the estrogens to a high degree: (1) >63%, NF and (2) >81.5% coagulation–NF.

Concentration of Inorganic Salts in the Permeate during Nano- or Ultrafiltration Promoted by Water-Soluble Polyelectrolytes in the Feed Solution

Nano- or ultrafiltration of inorganic salts in the presence of a polyelectrolyte in the feed solution is investigated in this work. The membranes are completely impermeable to the polyelectrolyte. At low concentrations of polyelectrolyte, a gel layer on the membrane surface is not formed. At such polyelectrolyte concentrations, the concentration of inorganic salt in the permeate stream can be higher than that in the feed solution. This salt concentration effect is the reverse of what is obtained with conventional membrane processes, where the permeate salt concentration is lower than, or equal to, the salt concentration in the feed solution. It is shown that, in the nano- or ultrafiltration of inorganic salts in the presence of a polyelectrolyte, the ratio of the salt concentration in the permeate to that in the feed is improved when the initial salt concentration in the feed solution is low. Concentration polarization has a negative impact on this concentrating effect. A theory that elucidates the observed phenomenon is presented, together with experimental data for potassium chloride solutions and N,N-dimethyl-N-2-propenyl-2-propen-1-aminium chloride homopolymer filtered on an ultrafilter with a pore size of 5 nm.

Pore Assembled Multilayers of Charged Polypeptides in Microporous Membranes for Ion Separation

In this study, highly permeable ion-selective membranes are prepared via immobilization of polyelectrolyte multilayer networks within the inner pore structure of a microporous (pore size = 0.2 microm) support. Electrostatic layer-by-layer assembly is achieved through alternate adsorption of cationic and anionic polyelectrolytes under convective flow conditions. To initiate pore assembly, the first layer consists of covalently bound charged polypeptides (poly(L-glutamic acid) (PLGA) or poly(L-lysine) (PLL)) establishing a charged support for subsequent adsorption. Nonstoichiometric immobilization of charged multilayers within a confined pore geometry leads to an enhanced volume density of ionizable groups in the membrane phase. This overall increase in the effective charge density allows for Donnan exclusion of ionic species (especially divalent co-ions) using microporous materials characterized by permeability values that exceed conventional membrane processes. Multilayer assemblies are fabricated using both PLGA/PLL and synthetic polyelectrolytes (poly(styrenesulfonate)/poly(allylamine)) in an attempt to compare the level of adsorption and separation properties of the resulting materials. The role of salt concentration in the carrier solvent on overall polyelectrolyte adsorption was examined to determine its effect on both solute (Cl-, SO4(2-), As(V)) and water transport. Constriction of the pore size induced by multilayer propagation was monitored through permeability measurements and dextran rejection studies at each stage of the deposition process.

Membrane application to water purification process in Japan – development of hybrid membrane system

This paper deals with two recent developments made by the authors about the hybrid membrane systems applicable to the water purification. The performance of a hybrid MF membrane system with circulating powdered activated carbon and condensed sludge has been studied using a pilot plant. The powdered activated carbon was intermittently dosed to the system for adsorbing mainly the humic substances. Manganese ions and ammonia nitrogen were biologically oxidized by the iron-oxidizing bacteria and ammonia oxidizing bacteria inhibiting the condensed sludge. In the hybrid MF membrane system, decreasing rate of the permeability was much less than that of a conventional MF membrane process. This may result from the reduced organic loading to the membrane due to the adsorption of humic substances onto the powdered activated carbons. A novel UF membrane process was also developed, where the nitrifying bacteria are fixed on the surface of the rotating disk membranes. With this membrane process, the simultaneous performance of the strict solid-liquid separation and the biological ammonia oxidation are possible. In order to increase the washing efficiency, a small quantity of the sponge particles were introduced into the membrane chamber and then the disk rotational speed was increased. This membrane washing method using sponge particles was so effective that the filtration resistance due to the accumulated cake was completely cancelled.

Removal of soluble organics and manganese by a hybrid MF hollow fiber membrane system

For the removal of turbidity, natural organic matter, manganese and ammoniannitrogen from river water, the performance of a hybrid MF membrane system with circulating powdered activated carbon (PAC) and sludge has been studied using a pilot plant. The PAC was intermittently added to the system for adsorbing the natural organic matter, mainly humic substances. Manganese ions and ammonia nitrogen were biologically oxidized by the iron-oxidizing bacteria and ammonia oxidizing bacteria inhibiting the sludge. While raw water temperatures were higher than 5°C, removal efficiency of soluble manganese and ammonia were almost 100%. However, removal efficiency decreased with decreasing water temperature. The removal efficiency of E260 was about 70% compared to 35% by the MF membrane filtration alone. In the hybrid MF membrane system, the decreasing rate of membrane permeability was much less than that of a conventional MF membrane process. This may result from the reduced organic loading to the membrane due to the adsorption of humic substances on the PAC.