Membrane Filtration Flux Research Articles

Submerged membrane adsorption hybrid system using four adsorbents to remove nitrate from water.

Nitrate contamination of ground and surface waters causes environmental pollution and human health problems in many parts of the world. This study tests the nitrate removal efficiencies of two ion exchange resins (Dowex 21K XLT and iron-modified Dowex 21K XLT (Dowex-Fe)) and two chemically modified bio-adsorbents (amine-grafted corn cob (AG corn cob) and amine-grafted coconut copra (AG coconut copra)) using a dynamic adsorption treatment system. A submerged membrane (microfiltration) adsorption hybrid system (SMAHS) was used for the continuous removal of nitrate with a minimal amount of adsorbents. The efficiency of membrane filtration flux and replacement rate of adsorbent were studied to determine suitable operating conditions to maintain the effluent nitrate concentration below the WHO drinking standard limit of 11.3mg N/L. The volume of water treated and the amount of nitrate adsorbed per gramme of adsorbent for all four flux tested were in the order Dowex-Fe>Dowex>AG coconut copra>AG corn cob. The volumes of water treated (L/g adsorbent) were 0.91 and 1.85, and the amount of nitrate removed (mg N/g adsorbent) were 9.8 and 22.2 for AG corn cob and Dowex-Fe, respectively, at a flux of 15L/(m2/h).

Pre‐ultrafiltration or pre‐ozonation for EDCs removal in a combined ultrafiltration and ozonation process

AbstractBACKGROUNDUltrafiltration (UF) coupled with ozonation (O3) may be a promising process for removing endocrine disrupting chemicals (EDCs) from secondary effluent. One key point in employing this process is whether the UF unit should be set in front of or after the O3 unit. So, in this paper, two systems with reversing series of UF and O3 units were developed and operated to assess which one is better.RESULTSResults showed that the O3‐UF process exhibited 13% higher UV adsorption removal efficiency than the UF‐O3 process. EDCs concentration and estrogenicity removal efficiency of the O3‐UF process was 2–7% and 10%, respectively, greater than that of the UF‐O3 process. In addition, the O3‐UF process achieved higher membrane filtration flux (28.9 LMH) than that (25.6 LMH) of the UF‐O3 process. A pilot scale O3‐UF reactor was designed to treat a real secondary effluent and achieved effective EDCs removal (average 75.2%) and estrogenicity removal (average 84.3%).CONCLUSIONSThis study indicated that the O3‐UF process can effectively remove EDCs from secondary effluent and produced weaker membrane fouling than the UF‐O3 process; therefore, it was suggested for treating EDCs‐containing secondary effluent. © 2016 Society of Chemical Industry

Enhancement of Lutein Yield from Coagulated Chlorella sp. ESP-6 with Sodium Hypochlorite

Applying coagulant such as polyaluminum chloride (PACl) or chitosan can improve harvesting efficiency of microalgae from broth. However, the coagulant molecules have affinity to lutein molecules, so coagulation reduces the lutein yield. This work proposed the addition of NaOCl with coagulant for enhancing lutein recovery from Chlorella sp. ESP-6 cells. Adding PACl or chitosan largely enhanced membrane filtration flux but had no effects on residual solid contents of filter cake. NaOCl released insoluble substances from the biomass matrix and deteriorated soluble lutein in water. When both NaOCl and coagulant were presented, the NaOCl helped to release the lutein out of the biomass, while the PACl and chitosan molecules assisted in capturing the OCl– ions. A practical harvest scheme including applying both PACl and NaOCl to optimize coagulation and maximum yield from Chlorella sp. ESP-6 biomass was discussed.

Coagulation–Membrane Filtration of Chlorella vulgaris at Different Growth Phases

Coagulation and membrane filtration separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was studied at different growth stages of algal cells using chitosan as the coagulant and a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane as the filter medium. Three samples were collected and tested: sample A in a logarithmic growth phase, sample B in a late stage of the growth phase, and sample C in a stationary phase. Sample A revealed efficient autocoagulation capability and samples B and C had poor settleability. The coagulation efficiency of algal suspension was increased with increasing chitosan dosage, reaching 99.7% removal rate at 200 mg L−1 chitosan for sample A, 99.5% removal rate at 50 mg L−1 chitosan for sample B, and 99.0% removal rate at 100 mg L−1 chitosan for sample C. Sample A, coagulated with 50 mg L−1 chitosan, had a membrane filtration flux of 10–14 m3/m2-min after a 5-min test. Samples B and C had poor filterability with membrane flux of less than 1.0 m3/m2-min after a 5-min test. Chitosan coagulation could incrementally enhance the filterability of samples B and C. Conversely, the solid contents in filtered cake from original samples A, B, and C were 26.8, 31.9, and 33.7%, respectively. That is, a long cultivation time led to a dry filtered cake after membrane filtration. Adding chitosan slightly decreased the solids content of the filtered cake from sample A, largely reduced the solids content from sample B, and first increased and then decreased the solids content of the filtered cake of sample C. Low water–solid binding energy corresponded to a dry cake after membrane filtration. Selection of the appropriate harvesting time and the required chitosan dose relies on the cost of membrane operation, coagulation operation, and subsequent drying steps. Supplemental materials are available for this article. Go to the publisher's online edition of Drying Technology to view the free supplemental file.

Chitosan coagulation–membrane filtration of Chlorella vulgaris

Filtration separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was studied using a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane. Coagulation using chitosan effectively removed turbidity at >100 mg l−1 chitosan. The membrane filtration flux at 1 bar was increased with chitosan dose. The filtered cake at the end of filtration tests peaked in solid content at 100 mg l−1 chitosan, reaching 30.5% w/w, about 50% higher than that of the original suspension. Coagulation using 100 mg l−1 chitosan followed by PTFE membrane filtration at 1 bar is a feasible process to harvest C. vulgaris from the algal froth.

Coagulation-membrane filtration of Chlorella vulgaris

Filtration-based separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was investigated using a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane. Coagulation using polyaluminum chloride (PACl) attained maximum turbidity removal at 200mgL−1 as Al2O3. The membrane filtration flux at 1bar increased as the PACl dose increased, regardless of overdosing in the coagulation stage. The filtered cake at the end of filtration tests peaked in solid content at 10mgL−1 as Al2O3, reaching 34% w/w, roughly two times that of the original suspension. Differential scanning calorimetry (DSC) tests demonstrate that the cake with minimum water–solid binding strength produced the driest filter cake. Coagulation using 10mgL−1 PACl as Al2O3, followed by PTFE membrane filtration at 1bar, is an effective process for harvesting C. vulgaris from algal froth.

Simulation of Countercurrent Operation of Two-Stage Hybrid PAC-Submerged Membrane System for Trace Organics Removal

A countercurrent two-stage hybrid powdered activated carbon-submerged membrane (PAC-SM) system for atrazine removal was simulated numerically in the present work. The simulation of the system performance at different operating conditions confirms that the adsorption capacity of the powdered activated carbon (PAC) can be further utilized and a stable product water quality can be maintained in the countercurrent two-stage mode as compared with the concurrent single-stage operations. For instance, the utilization of the PAC adsorption capacity was enhanced by 28% in the countercurrent two-stage operation at a flux of 60 L/m2h, and 21% of enhancement was obtained at a flux of 100 L/m2h by more frequent PAC replacement. Therefore, the adsorption capacity utilization is also dependent on the membrane filtration flux. Moreover, if the final effluent concentration was controlled at a higher level (e.g., C2*=0.1 instead of C2*=0.05), a further 5% of the PAC adsorption capacity can be utilized. In addition, reducing the replacement rate (RR) will make the operation similar to a system with continuous PAC dosing (pseudo-steady-state) by presenting nearly constant product water quality. This study sheds some light on the performance of a countercurrent multistage hybrid PAC-SM system for its further applications and system optimization.

Modeling cake filtration under coupled hydraulic, electric and osmotic effects

Pore blocking is considered to dominate the dewatering efficiency in filtration processes. Various engineering measures were adopted to promote the permeate flux of membrane filtration, e.g. electro-osmosis, flocculation and aggregation, membrane flush and pressure adjustment. A new model was proposed to address the coupling effect of hydraulic, electric and osmotic fields on cake filtration on the basis of thorough review on relevant researches. A moving boundary was configured to evaluate the time-dependent cake growth behavior. An instant mass balance was assumed valid at the cake–slurry interface, which was shown to reflect the experimental facts. The coupled governing equations were solved numerically by finite element method (FEM), and were validated by comparing with experimental results. The nonlinear constitutive behaviors of the filter cake under varied pressure head were further included in the models. FEM analysis indicates that the hydraulic conductivity and electro-osmotic coefficient of the formed cake are critical for the permeation flux. Correspondingly the pressure head and electrical potential gradient applied to the filtration system largely determine the separation efficiency. The filter cake (FC) formed in front of membrane filter contributes a lot to the reduction in solvent flux under certain dewatering conditions. Measures to improve the flocculation behavior of dispersible sludge were explained by the new model. Modifying the surface charge of sludge with polyelectrolyte is found to benefit the dewatering only within a limited time/leachate range, which was reported for the first time. Suggestions on cake filtration were provided according to our numerical simulations.

The difference in characteristics of foulants in submerged MBRs caused by the difference in the membrane flux

The main obstacle for a wider use of membrane bioreactors (MBRs) for wastewater treatment is membrane fouling, which increases operating costs. For a more efficient control of membrane fouling in MBRs, an understanding of the mechanisms of membrane fouling is important. We conducted two separate pilot-scale experiments using real municipal wastewater to investigate the influence of the membrane flux in MBRs on the characteristics of foulants, which were analyzed by Fourier transform infrared (FTIR) spectra, 13C nuclear magnetic resonance (NMR) spectra, monosaccharide composition and amino acid analyses. In each experiment, two identical membrane modules were submerged in the same MBR tank and were operated under different membrane fluxes. The results obtained in this study indicated that the membrane filtration flux significantly influenced membrane fouling in MBRs. Membrane fouling in the module operated with the higher flux was much greater than that of the other on the basis of the volume of filtered mixed liquor suspension. Analyses of the foulants desorbed from the fouled membranes revealed that the nature of the foulants significantly differed depending on the membrane flux despite the fact that the two modules filtered the same mixed liquor suspension at the same time. The difference in characteristics of the foulants caused by the difference in the membrane flux was similar in the two separate experiments, indicating that reproducibility of the data was sufficient. It was thought that different fractions of the mixed liquor suspension were transported to the surfaces of the membranes depending on the membrane flux and subsequently caused membrane fouling to different extents. The foulant desorbed from the membrane operated with a higher flux seemed to cause severer fouling than the foulant desorbed from the other membrane.

Membrane Fouling in Pilot-Scale Membrane Bioreactors (MBRs) Treating Municipal Wastewater

The main obstacle for wider use of membrane bioreactors (MBRs) for wastewater treatment is membrane fouling (i.e., deterioration of membrane permeability),which increases operating costs. For more efficient control of membrane fouling in MBRs, an understanding of the mechanisms of membrane fouling is important. However, there is a lack of information on membrane fouling in MBRs, especially information on features of components that are responsible for the fouling. We conducted a pilot-scale experiment using real municipal wastewater with three identical MBRs under different operating conditions. The results obtained in this study suggested that the food-microorganisms ratio (F/M) and membrane filtration flux were the important operating parameters that significantly influenced membrane fouling in MBRs. Neither concentrations of dissolved organic matter in the reactors nor viscosity of mixed liquor, which have been thought to have influences on fouling in MBRs, showed clear relationships with membrane fouling in this study. Organic substances that had caused the membrane fouling were desorbed from fouled membranes of the MBRs at the termination of the operation and were subjected to Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (NMR) analyses. These analyses revealed that the nature of the membrane foulant changes depending on F/M. It was shown that high F/M would make the foulant more proteinaceous. Carbohydrates were dominant in membrane foulants in this study, while features of humic substances were not apparent.

Nanofiltration of solutions containing surfactants—prediction of flux decline and modelling of mass transfer

Nanofiltration (NF) membranes are capable of separating surfactants from aqueous solutions with very high retentions. For the anionic surfactant sodium dodecylether sulfate (SDES) retentions exceeding 99.9% referring to the feed concentration have been found. The decrease of the permeate flux compared to the pure water flux in membrane filtration of solutions with surfactants is difficult to predict. In order to simplify membrane selection for a separation problem, an attempt is made to correlate flux decline due to adsorption to the contact angle measured on UF/NF membranes. The vague dependence shown cannot replace membrane screening. In the second part of the paper, a mass transfer model for NF of surfactant solutions based on the extended Nernst—Planck equation is presented. Convective mass transfer of the solute is included in the model, as well as the influence of adsorption of surfactant and concentration polarisation.

304 膜分離技術を用いた浄水場内排水回収システムの改善

This paper describes an experimental study for the purpose of water quality improvement on wastewater (e. g. rapid sand filter backwashing drainage) recycling system in water purification plant, combined roughing filter and tank-submerged ceramic membrane filtration. Consequently, in this system, it was stably demonstrated that high removal rate of suspended solid and metal, such as iron, manganese aluminum and so on. And, membrane process could perform stable operation with membrane filtration flux 0.8m^3/m^2/day. Moreover, by arranging a sludge sedimentation zone at the bottom of membrane tank, the sludge concentration with the surroundings of the membrane was kept low, and cake accumulation on membrane surface was reduced. In the result, about 4∿5% of concentrated sludge was able to be obtained stably.

Influence of shear on flux in membrane filtration of integrated pulp and paper mill circulation water

Different ultrafilters and membranes were tested with ground wood mill circulation water from an integrated pulp and paper mill. Both the CR 200/1 (cross rotational, CR-filter™) and the VSEP ® L (vibratory shear enhanced processing) laboratory modules and the CR 1000/10 pilot plant module were investigated. In the pilot plant filtration the effects of the rotor speed, volume reduction factor and pressure were tested. According to the measurements, the lower the pressure and the higher the rotational frequency (CR 200/1) or the vibration amplitude (VSEP L), the less fouling occurred. For the CR-modules the best short time fluxes were obtained with PA 50H and Desal JX membranes, and for the VSEP-module with the PA 50H and C 30F membranes. The C 30F, PA 50H and PES 50H membranes were chosen for the pilot plant filtrations. In the pilot tests at the mill it was observed that the hydrophilic C 30F membranes fouled very little and had fluxes close to 400 l/(m 2h). The more hydrophobic PA 50H and PES 50H membranes were fouled badly, and cleaning only restored flux for a short time. A concentration factor between 10 and 30 did not influence the flux very much, but inside the equipment the membranes handling the highest concentration had a lower flux. Also in the mill site experiments it was shown that the flux should be kept as close to the critical flux as possible and that this could be achieved with a high cross-flow velocity and the lowest pressure possible for the equipment.

Membrane filtration of surface water in the presence of ozone

The preliminary study investigated the effect of pre-ozonation of synthetic raw water (bentonite and humic acid) on membrane fouling. The results showed that humic acid, not bentonite, was the dominant factor in membrane fouling. When the synthetic raw water was pre-treated using ozone and activated carbon, stable operation was possible at twice the flux of membrane filtration without pre-treatment. Thus, ozone and activated carbon reduced the concentration of organic matter (humic acid), leading to an increase in flux. Secondly, an MF membrane filtration device with ozone tolerance was attached downstream of the ozone reactor so that residual ozone could reach the membrane surface. When water was treated with MF membrane filtration in the presence of ozone, the flux was stable at 4 m/d. The membrane filtration resistance increased when ozone was not injected, and decreased when it was injected. This phenomenon was repeatable. In the presence of ozone, organic matter that could accelerate fouling as decomposed and converted to less fouled materials, resulting in a suppression of fouling as well as facilitating removal of the fouling layer during back washing.

Advanced water treatment system using ozone and ozone resistant microfiltration module

In order to achieve an efficient and economical advanced drinking water system, the relationship between operating conditions, membrane filtration flux and water qualities was examined by using a pilot plant consisting of ozonation facility, ozone resistant microfiltration (MF) module and granular activated carbon (GAC) tower. It was found that keeping residual ozone of more than 0.3 mg/L on the membrane surface is necessary in order to obtain a high membrane filtration flux. Withy ozone dosage of 3 mg/L by ejector and filtration by dead-end mode, this new system provided a high membrane filtration flux of more than 5 m3/m2/day. Quality of the produced water from the GAC tower was meeting the drinking water standard.

Factors influencing critical flux in membrane filtration of activated sludge

Membrane filtration of biomass is usually accompanied by significant flux decline due to cake-layer formation and fouling. Crossflow filtration with flux controlled by pumping the permeate can produce stable fluxes if a ‘critical flux’ is not exceeded. Below critical flux the transmembrane pressure is typically very low and increases linearly with imposed flux. Above the critical flux the transmembrane pressure rises rapidly signifying cake-layer formation which is usually accompanied by a continued rise in transmembrane pressure and/or a drop in delivered flux. A range of microfiltration and ultrafiltration membranes with pore sizes from 0.22 to 0.65 µm and molecular weight cut-off of 100 kDa was used. The feed was an activated sludge mixed liquor with concentration in the range of 3–10 g dm−3. The results show that the critical flux depends on feed concentration and crossflow velocity, being higher for higher crossflow velocity or lower feed concentration. Critical flux was also dependent on membrane type, being lower for hydrophobic membranes. Although the transmembrane pressure was higher for the larger pore size membrane, no significant difference in critical flux was observed among different pore size membranes. © 1999 Society of Chemical Industry

The Effect of Operating Conditions on Critical Flux in Membrane Filtration of Latexes

In microporous membrane filtration, formation of a cake of solids results influx decline. Pumping the permeate can remove the deposited layer and improve the flux. This technique allows operation at low transmembrane pressure and provides stable flux if a ‘critical flux’ is not exceeded. Slow fouling can occur in time if the initial flux is beyond the critical value. Critical flux is dependent on the factors that influence concentration polarization, such as nature and concentration of the feed and shear rate, being higher for higher crossflow velocity and lower concentration. These effects have been observed for activated sludge biomass. However, the complexity of the biomass can affect the dependency of critical flux on operating conditions. Well characterized polystyrene latex particles were used to explain the factors influencing critical flux in a colloidal suspension without taking into account the complex nature of the feed. The main difference between these feeds was that the pumped permeate flux was significantly lower in the activated sludge than in the pure water flux. In the latex suspension the same flux was obtained for the feed and for the pure water. However, the same trend for factors affecting critical flux was observed in the activated sludge biomass and latex suspension.

An Investigation of the Mechanism of Critical Flux in Membrane Filtration Using Electron Microscopy

The critical fluxes for colloidal latex suspensions of 1.0 µm and 0.1 µm and their mixture were measured. The similar fluxes were observed for latex suspensions and pure water. Electron microscopy was used as a tool for critical flux mechanism investigation.