Microfiltration Membrane System Research Articles

Modelling of particle deposition in a submerged membrane microfiltration system

In this study, microfiltration of a concentrated suspension of kaolin clay was performed in an aerated tank with submerged flat sheet membranes. Particle deposition was correlated with cake resistance based on experimental results. The effects of air flow rate and permeate flux on transmembrane pressure (TMP) and on membrane resistance were studied. The experimental results show that the filtration resistance due to cake formation plays a dominant role in the total filtration resistance. An increase in permeate flux caused higher TMP development due to an increased amount of particle deposition. Conversely, an increase in air flow rate reduced TMP by detaching deposited layers back into suspension. The particle deposition under different filtration flux and air flow rates was correlated to establish an empirical formula. Based on the experimental results, a general relationship between the cake resistance, permeate flux and particle deposition was derived as Rc=1.01×1012J·wc that suggests that the cake resistance is proportional to the multiplication of flux and cake deposition. Moreover, the effect of air flow on cake porosity was observed to be more significant at low permeate flux.

Application Research of Microfiltration Membrane Pilot Test in Water Treatment

Lake water is used as the raw water. The water carries the following characteristics: high organic content in individual sessions, high-algae and odor in summer. At present, the conventional treatment process is unable to cope with. The application of microfiltration system in the pilot test is studied. Filter effluent and air flotation effluent are used as the microfiltration influent. Membrane flux are 80L/m2/h, 90L/m2/h, 100L/m2/h.Water quality is stable. The average turbidity is 0.1NTU. Total coliform and total bacteria in effluent are not detected. The recovery of water is greater than 96.1%.Potassium permanganate preoxidation + powder carbon dosing + conventional treatment + microfiltration membrane system can effectively solve organics, high algae and odor problems. It also can improve the coping capacity to respond mutation of the water quality.

A study on enhancing physical cleaning effectiveness in microfiltration membrane system

Fouling control is generally taken by selective pre-treatments, proper membrane operation conditions, and various membrane cleaning methods. The compactness and growth of cake layer on the membrane surface should be timely controlled by mechanical force or hydraulic action. In this work, the sequence of physical cleaning method was strategically introduced by changing cross-flow velocity (CFV), backwash intensity, and backwash waste discharge method from membrane housing. Intensive backwash flush was automatically applied when delta TMP obtained after backwash events was more than 2%. It provided higher pressure on the permeate side of the membrane compared to the normal backwashing, resulting in the reduction of sharp increase of TMP during several operation modes. In addition, the variation of CFV from 0 to 16 m/d based on the membrane fouling index caused turbulence on the membrane fiber, resulting in the discharge of particles accumulated on the membrane surface from membrane module. Finally, flushing mode followed by filtration was more effective in maintaining the TMP stable rather than discharging mode. Flushing effect could induce another shear force to the suspended solids in the bulk and remove cleaning wastes effectively from membrane housing. Large particulates and colloidal matters could be controlled by the proper sequence of physical cleaning based on the TMP monitoring. Furthermore, the strategic physical cleaning could sufficiently reduce not only TMP increase but also the damage of membrane, which is resulted from the more frequent and aggressive chemical cleanings.

Microspheroidization treatment of macroporous TiO2 to enhance its recycling and prevent membrane fouling of photocatalysis–membrane system

Patterned porous (PP)-TiO2/calcium–alginate (CA) microspheres with an average diameter of 3 mm were prepared by immobilizing PP-TiO2 into CA balls to improve their recycling and photoactivity. The microspheres demonstrate higher degradation activity on methylene blue (MB) than Degussa P-25 nanoparticle/CA (P25-TiO2/CA) spheres, freely suspended PP-TiO2, and P25-TiO2 fine particles. Furthermore, the microspheres can be easily recycled. Meanwhile, the energy cost in the recycling of PP-TiO2 is 1.23 × 108 J per gram PP-TiO2. The PP-TiO2/CA microsphere combined polyacrylonitrile (PAN) microfiltration membrane system was established to dispose of the MB wastewater. Compared with the PP-TiO2 catalyst–membrane system, the PP-TiO2/CA microsphere–membrane system can achieve almost 90% degradation ratio of MB. The permeation flux for the combined system is approximately the same as that of the PAN membrane and remains at 90 L/m2 h. However, the permeation flux decreases to 70 L/m2 h when freely suspended PP-TiO2 is used as photocatalyst. The reason is that with the operation going on, the PP-TiO2 cake layer is formed by a growing number of suspended PP-TiO2 particles depositing on the membrane surface. The deposition induces membrane fouling and inhibits the photocatalysis activity of PP-TiO2 in the solution, whereas PP-TiO2/CA microspheres remain suspended in the solution under gentle stirring. Moreover, the sum of drag force FD and buoyancy Fb (FD + Fb = 1.552 × 10−4 N) imposed on the microsphere was calculated to be comparable with the gravity G (1.566 × 10−4 N) of the PP-TiO2/CA microsphere. This result further reveals that the microspheres are suspended in the dye solution, thereby preventing membrane fouling. We believe that the microspheroidization of PP-TiO2 and the combined microsphere–membrane system provide a new idea for practical wastewater treatment.

Functionalized electrospun nanofibrous microfiltration membranes for removal of bacteria and viruses

A novel nanofibrous microfiltration membrane system, fabricated from surface functionalized polyacrylonitrile (PAN) electrospun nanofibers, was demonstrated for the effective removal of bacteria and viruses from contaminated water. For membrane modification, dual-vinyl and tri-vinyl monomers were polymerized on the surface of the PAN electrospun nanofibers, which also improved the membrane mechanical properties due to the formation of a cross-linked. Meanwhile, the dual-vinyl monomer with an imidazolium cation resulted in positively charged electrospun PAN nanofibers, allowing the membrane to create not only 2–3 times higher permeation flux or lower pressure drop, but also 99.9999% retention of bacteria (e.g., Escherichia coli) and 99.99% retention of bacteriophage (e.g., MS2) during microfiltration when compared with commercial microfiltration membranes (e.g., 90% retention of MS2).

The Optimization of Operation Parameters of Microfiltration Membrane System

The sustainable flux in dead-end mode of MF membrane filtration was confirmed in this study. Analytic results show that when flux above which an irreversible deposit (fouling) appears. The sustainable flux is dependent on the hydrodynamics and system properties (pH, ionic strength, membrane characteristics, particle characteristics, etc) and position along the membrane. Below the sustainable flux, tiny fouling is observed. In addition, the optimal pre-coagulation condition was found based on the maximum turbidity and organic remove rate.

Strategies for the recovery of nutrients and metals from anaerobically digested dairy farm sludge using cross-flow microfiltration

This work reports on the recovery of nutrients and metals from anaerobically digested manure sludge using a pilot scale microfiltration membrane system. Soluble nitrogen (N), phosphorous (P) and metals are valuable commodities which exist in high concentration in anaerobically digested manure sludge. The typical disposal of sludge on farmland can cause serious harm to the ecosystem due to eutrophication. The recovery of these materials in clarified solutions represents an added value product and a less contaminated sludge that is environmentally less hazardous.The objective of this study was to investigate the recovery of nutrients and metals using a pilot scale cross-flow membrane filtration system. A ceramic membrane of 0.22 m2 and 0.2 μm pore size was used to perform solid–liquid separations and soluble materials were recovered in particle and bacteria free solutions. Strategies such as batch diafiltration (DF) and acid pre-treatment were investigated and the fractions collected compared against the initial permeate containing 686.2 mg NH3–N L−1 and 41.51 mg PO4–P L−1. Clarified fractions obtained through DF with no acid pre-treatment yielded N:P ratios of around 30 and relatively low levels of P (364.24 mg NH3–N L−1 and 25.60 mg PO4–P L−1) and metals. Acid pre-treatment of the sludge resulted in a two-fold increase of P extracted (271.11 mg NH3–N L−1 and 71.60 mg PO4–P L−1), altering N:P ratios to 8. Depending on the metal species, a 2–9 fold increase in concentration was also observed. Thus it has been demonstrated that different treatment strategies influence the removal and recovery of nutrients and metals from sludge. The best treatment conditions therefore depend on the targeted materials to be recovered. By careful manipulation of the treatment processes the production of specific nutrient compositions in terms of N:P ratios is possible.

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.

Significance of flocculation for NOM removal by coagulation–ceramic membrane microfiltration

Potable water treatment with coupling coagulation–microfiltration processes are still rarely applied in commercial treatment plants. Raw water with a high content of organic matter, typical for Norwegian surface water sources, was treated in this study using a ceramic microfiltration membrane system. Three different pre-treatment options were investigated, a classical two-stage flocculation, a simplified one-stage fast mixing step and an inline flocculation treatment, using an iron chloride coagulant. DOC removal was similar (76–81%, 5.5 mg C/L in raw water) in all compared setups. The more compact, energy efficient inline configuration was investigated further, varying flux (140 and 220 LMH), pH (4.5, 5.5 & 6.5), G-value (60 and 300 s−1) and HRT in the pipe (7 and 30 s), while monitoring DOC removal, fouling rate and residual iron concentrations. DOC removal was strongly pH dependent; 70% at pH 4.5, and 47% at pH 6.5. At high flux of 220 LMH the membrane fouled quickly and sustainable operation was not possible. At 140 LMH fouling was much less and no severe fouling was observed during the experimental period. Residual metal concentration was found to be the limiting parameter in the design and operation of the process configuration. Metal concentrations below the regulation limits (200 μgFe/L) were only achieved at pH 6.5. Reversible fouling was only observed at higher pH values.

Effect of fouling reduction by ozone backwashing in a microfiltration system with advanced new membrane material

The effect of ozone back washing for membrane fouling reduction was experimentally investigated in a submerged metal membrane microfiltration system. A cleaning by intermittent ozone gas backwashing was effective in recovering the permeation flux. Intermittent ozone backwashing was highly effective than the air or permeates backwashing for flux recovery. Regarding the operational parameters, the increase of ozone gas flow rate was more effective than the increase of injection time under the conditions of same ozone dose. However, the backwashing cycle was longer, the effect of flux recovery by ozone backwashing decreased. Therefore, it is favorable to operate membrane cleaning before the foulant was consolidated on membrane surface.

TREATMENT OF RICE COOKER WASTEWATER AND RECOVERY OF BY-PRODUCTS BY MEMBRANE MICROFILTRATION

A pilot scale system was used to evaluate the performance of a membrane microfiltration system, rated at 0.1 micron, for the recovery of starches and other solids from rice cooker wastewater produced by a rice processing facility. The first series of tests revealed that a crossflow velocity (V) of 5 m/s and a transmembrane pressure (TMP) of 275 kPa were appropriate for filtration. In the next series of tests, a concentration of almost 9% total solids was achieved, and the logarithmic relationship between permeate flux and concentration was described. Permeate flux rates decreased from over 80 L/m2*hour (LMH) for unconcentrated samples to under 20 LMH for the most concentrated samples. The feed flow contained an average of 0.71% total solids and 4395-mg/L biochemical oxygen demand (BOD). The permeate contained under 0.10% total solids and 330 mg/L BOD. A membrane system was sized for the test site based on data from these experiments. A system capable of concentrating 68 L/min of cook water to 5%, 8%, and 10% total solids required a total membrane surface area of 75, 100, and 115 m2, respectively. The reduction in sewage expense was predicted to average $10.48 per hour of operation.

A PILOT STUDY DESIGNED TO DEFINE THE OPERATING PROTOCOL FOR A MULTIPLE BARRIER MEMBRANE SYSTEM

A PILOT STUDY DESIGNED TO DEFINE THE OPERATING PROTOCOL FOR A MULTIPLE BARRIER MEMBRANE SYSTEMA pilot scale cloth media disk filtration system and microfiltration membrane system were installed in series at the University of California – Davis wastewater treatment plant to process secondary effluent. The purpose of the study was to define the operating protocol for the entire system that would allow for the maximum sustainable membrane flux, while still providing a high quality...Author(s)Nick TookerJeannie DarbyGeorge TchobanoglousKen MikkelsonLloyd JohnsonSourceProceedings of the Water Environment FederationSubjectSession 53: Membranes and TechnologyDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2004ISSN1938-6478SICI1938-6478(20040101)2004:11L.133;1-DOI10.2175/193864704784136324Volume / Issue2004 / 11Content sourceWEFTECFirst / last page(s)133 - 140Copyright2004Word count138

The effect of particulate material and the loading of bacteria on a high dose PAC-MF system

The effects of particulate material, their size distribution and the loading of total bacteria based on the age distribution of powdered activated carbon (PAC) were investigated in a hybrid membrane process consisting of an immersed microfiltration membrane system in a completely aerated reactor containing high concentration (40 g/L) of PAC. The laboratory-scale experiments on PAC-MF system were carried out using actual surface water (Tama River, Tokyo), before and after the treatment by a biofilter media. As a result of continuous filtration and backwash experiments, improvement of filtrate water quality and controls of membrane fouling were demonstrated by the addition of PAC. 52% of the PAC fell into a particle size between 22 μm and 45 μm. PAC larger than 125 μm and smaller than 22 mm were 6% and 4% respectively. Due to continuous aeration and Brownian motion of the particles, the size of the PAC inside the reactor was becoming smaller day by day. After 162 days of operation, the particle size from 1-10 μm was higher, which is the suitable size range for the adsorption of bacteria. At the same time, the number of total bacteria was also increasing inside the reactors. The membranes were fouled shortly during end of the operation due to the heavy load of fine particles and high accumulation of bacteria. However, PAC acts as an adsorbent media inside the reactors that causes successive accumulation of total bacteria.

Microfiltration of activated sludge wastewater—the effect of system operation parameters

Membrane or hollow fiber microfiltration is increasingly used with the activated sludge process in conventional wastewater treatment to produce a higher quality effluent. The major problem of such applications is membrane fouling, which has generally been attributed to the high contents of suspended solids in the wastewater. In this study, the operation of an integrated activated sludge bioreactor–membrane microfiltration system was investigated. It was found that the airflow rate of aeration, the mechanical mixing of the bioreactor and the circulation flow of the wastewater through the cross-flow microfiltration unit all affected the size distribution of the particles in the wastewater to be filtered, which consequently affected the performance of the microfiltration unit. The degree of membrane fouling by different size fractions of particles in the activated sludge wastewater was examined. The results reveal that the smaller particles played a more important role in membrane fouling. A relatively simple model is presented to predict cake growth and permeation flux decline in a cross-flow microfiltration.

Effect of natural organic matter loading on the atrazine adsorption capacity of an aging powdered activated carbon slurry

The effect of natural organic matter loading and calcium carbonate precipitate towards atrazine adsorption capacity of an aging powdered activated carbon slurry was investigated in an hybrid membrane process consisting of an immersed microfiltration membrane system in a completely stirred tank reactor containing powdered activated carbon. The reactor was fed with clarified Seine river water containing natural organic matter (NOM). Samples of the slurry were taken from the reactor and dried at low temperature to avoid the adsorbed NOM degradation. Thermal and CaCO 3 analyses were carried out to characterize each sample. The adsorption capacity of each sample was measured by the classical method of isotherms, a modelling method was applied to predict the adsorption capacity in natural water. Kinetic experiments were carried out and the results were also modelized to determine kinetic parameters ( k f and D s). The isotherms showed a significant decrease of the capacity during the 62 d of aging (from 3.4 to 0.4 mg g −1 for an equilibrium concentration of 0.1 μg L −1 in distilled-deionized water). A linear relationship was found between the Freundlich constant K and the age ( r 2>0.9). The kinetic experiments showed also the decrease of the D s value (from 1.16×10 −15 to 8.3×10 −17 m 2 s −1) while k f remained constant and appeared as a non-limiting parameter. Operating charts based on these results were drawn as tools for operators giving operating conditions (age of PAC slurry and fresh PAC dosage rate) to remove a given concentration of atrazine.

Effects of backwash conditions on out-to-in membrane microfiltration

North West Water Ltd (NWW) has applied hollow-fibre membrane microfiltration (MF) for treatment of potable water at full scale (15–80 MLD). NWW has currently five MF plants either in operation, commissioning or under construction (total capacity 240 Ml/d). The adoption of this technology has been driven by a number of factors, one of which is to provide a barrier to Cryptosporidium. As part of the development of large systems, NWW's Technology Development Team have performed an extensive series of pilot trialling. The efficacy of the backwash is one of the key criteria in ensuring the efficient and effective operation of the MF system. This is particularly important with out-to-in hollow-fibre membrane systems, since the bundle of fibres can act as a depth filter and accumulate deposits from the feed water. Moreover, the internal membrane hydraulics of an out-to-in system, during backwash, is complex. This makes optimisation of the efficient removal of solids from the membrane surface, by the backwash, an important task. Poor flow distribution, within the membrane module, can lead to the development of areas of low flow rates or “dead areas”. There is a risk of solids accumulation, within these dead areas, which will lead to increased transmembrane pressure during production. Pilot plant trials have been performed to optimise the backwash conditions at all the sites at which NWW have applied MF. The work has explored a variety of parameters associated with the backwash operation, such as backwash pressure, interval, duration, volume, chemical assistance, fibre integrity and the use of water pulsing. Results show that all the variables must be addressed to develop an optimised backwash strategy. By optimising backwash pressure, interval, duration, volume and use of chemicals (oxidants) run times can be extended and hence operating costs controlled. The most promising results, in terms of removal of deposited foulant from the membrane surface, are obtained with the pulsed backwash, where the backwash water is delivered in a series of discrete pulses. These studies have clearly demonstrated that the majority of deposited material is detached from the membrane surface during the initial phase of the backwash. This suggests that the detachment mechanism is more likely to be mechanical, caused by the sudden expansion of the bundle, and not hydraulic shear. Optimisation of pulse duration, the interval between pulses and the number of pulses applied in any one backwash cycle, has been performed. It has been possible to show that after time a steady state is achieved and backwash efficiency approaches 100%. Interestingly, backwash efficiency was found to increase as a run progressed. At the outset of a run backwash efficiency was typically low (∼14%) and increased with time to nearly 100%. This indicates that some form of steady state system is in operation whereby the solids being removed from the system are a function of the incoming solids and the previously retained solids. The effect of fibre breakage on backwash efficiency, with an out-to-in membrane system was found to result in serious degradation of backwash efficiency. The likely explanation is that a broken fibre will take a significant proportion of the backwash flow. This effect was observed during pilot plant trials when backwash efficiency and permeate water quality deteriorated simultaneously. Subsequent bubble point tests revealed fibre breakage. Once this damage was repaired. backwash efficiency was restored.

Disinfection and Clarification of Treated Sewage by Advanced Microfiltration

A study was conducted to investigate the use of an advanced membrane microfiltration system to disinfect and clarify secondary and primary treated sewage. The membrane microfiltration system tested incorporated a patented gas backwashing technique which significantly reduces fouling. A comprehensive microbiological testing program established that all indicator bacteria and viruses were removed by this system. Testing for chemical quality showed significant reductions in BOD, suspended solids, turbidity, phosphorus, oil/grease and heavy metals. Consistent filtration rates over several months were achieved without significant biological fouling. The study conclusively showed the capability of the microfiltration system to disinfect and clarify treated sewage.