High Filtration Resistance Research Articles

Characteristics and fouling behaviors of soluble microbial products and sub-visible particles in an anaerobic membrane bioreactor treating sewage at room temperature

A lab-scale anaerobic membrane bioreactor (AnMBR) was employed to investigate the characteristics and fouling behaviors of soluble microbial products (SMP) and sub-visible particles (SVP) in sewage treatment. The study revealed a noteworthy trend, where SMP and SVP concentrations initially surged, subsequently declined, and ultimately stabilized at comparable levels. Compositions and fluorescent property analyses indicated that protein-like substances with tryptophan are the primary fluorescent composition in both SMP and SVP. Notably, SVP exhibited a superior protein concentration and a higher protein-to-polysaccharide ratio, thereby resulting in a higher filtration resistance than SMP. Moreover, microbial species involved in biofouling (Rhodocycales and Desulfovibrionales) also have a higher abundance in SVP, meaning SVP has a higher biofouling potential than SMP. Achievements in this study expanded the knowledge of the characteristics of SMP and SVP and revealed the significant role of SVP in membrane fouling of AnMBR.

Effect of operating condition on the properties of ectoine particles for improving the purification process

Ectoine, which is produced from methane by methane-oxidizing bacteria, has attracted attention because of its many useful functions in living organisms. It is known that the purification process using alcohol-based solvents is a limiting step in the ectoine production process because of the precipitation of fine particles. This study investigated quantitatively the effects of operating conditions (cooling rate and solvent) on the properties of ectoine particles for improving the efficiency of the ectoine purification process. The experimental results showed that the properties of ectoine particles were significantly influenced by operating condition such as the cooling rate and solvent of feed solution. Furthermore, it was revealed that the critical supersaturation ratio at the nucleation using methanol was approximately ten times higher than using water. Consequently, it was found that the high critical supersaturation ratio at the nucleation induces the precipitation the fine particles that have high filtration resistance. In conclusion, we succeeded in finding the relationship between the operating conditions and properties of ectoine particles.

Electro-assisted filtration of microfibrillated cellulose: the impact of the degree of fibrillation

AbstractEfficient dewatering is necessary to achieve an economically sustainable large-scale production of microfibrillated cellulose (MFC) because the low solids content of the final product (< 3 wt.%) results in high costs related to transportation and storage, and problems for products with water incompatibility. Mechanical dewatering is preferred to thermal drying due to its lower energy demand, but MFC has a very high filtration resistance, which implies that an excessive filter area is necessary. Thus, to improve the dewatering, electro-assisted filtration may be used. In this study a bench-scale dead-end filter press was modified and the electro-assisted filtration of MFC, with two degrees of fibrillation, was investigated. The impact of the degree of fibrillation was clear when either pressure or electric field were applied separately. It was more challenging to dewater MFC with a higher degree of fibrillation using conventional filtration due to a greater surface area being subjected to the liquid flow. The opposite was found when using an electric field alone: the more fibrillated material has a higher surface charge and thereby is impacted more by the electric field. A combination of pressure and electric field resulted in a greatly improved dewatering rate, but no significant difference could be observed between the two qualities. After dewatering, the water retention value was slightly decreased, but the material still showed a gel-like behaviour, although the network strength was slightly reduced, as seen by a reduction in yield stress, storage and loss moduli. This was plausibly due to a decrease in the surface area and/or deformed network.

Rational design of dopamine-decorated gradient structure membrane with novel hydrophibic/underwater-oleophobic for oil/water separation

The shortage of water resources and the aggravation of water pollution have become global environmental problems. The improvement of the separation performance and flux is still a key challenge that restrict the preparation of high-performance filtration membrane. The gradient structure fibrous membranes were designed and prepared using electrospinning nanofiber and polypropylene/low-melt- point polyester (PP/LPET) micro-fibrous and reinforced via needle-punching and hot-pressing. And the as-prepared membrane was functionalized and directly decorated by dopamine copolymerizes. The novel gradient membrane turned from a hydrophobic state to hydrophilic state, and had excellent mechanical and water transmission properties. Mostly importantly, the as-prepared hydrophilic gradient membranes showed durable oil-fouling repellency and the separation efficiency of oil/water mixture approximate 99% and the flux reach 10,278 ± 1512 L m−2 h−1. This method provides a feasible solution to overcome the high filtration resistance of electrospinning nanofiber membrane, as well as for the preparation of low-cost and high-performance composite membranes and structural regulation of functional membranes.

Study on the structure and filtration properties of intercalated melt blown nonwoven materials

Based on the traditional melt blown process, PET high crimp elastic staple fibers were added to construct an intercalated melt blown two-component filter material. The changes in structure and filter performance of the material before and after intercalation, and whether the intercalation rate had any effect on these changes were analyzed in this paper. The results showed that the intercalation operation was carried out to solve the problems of poor compression resilience of single melt blown nonwoven material and high filtration resistance of existing filtration materials. A multivariate nonlinear model was developed in this paper to investigate the variation of the product structure under different technological parameters, and a mathematical expression between them was given. A random forest model was used to investigate the variation of product performance under different product structures. Using a combination of multivariate nonlinear model and random forest model, the values of the technological parameters, when the filtration performance was maximum were explored. It can be used as a guide for melt blown nonwoven material production.

New technical concept for alternating tangential flow filtration in biotechnological cell separation processes.

Robust cell retention devices are key to successful cell culture perfusion. Currently, tangential flow filtration (TFF) and alternating tangential flow filtration (ATF) are most commonly used for this purpose. TFF, however, suffers from poor fouling mitigation, which leads to high filtration resistance and product retention, and ATF suffers from long residence times and cell accumulation. In this work, we propose a filtration system for alternating tangential flow filtration, which takes full advantage of the fouling mitigation effects of alternating flow and reduces cell accumulation. We have tested this novel setup in direct comparison with the XCell ATF® as well as TFF with a model feed comprising yeast cells and bovine serum albumin as protein at harsh permeate to feed flow conditions. We found that by avoiding the dead-end design of a diaphragm pump, the proposed filtration system exhibited a reduced filtration resistance by approximately 20% to 30% (depending on feed rate and permeate flow rate). A further improvement of the novel setup was reached by optimization of phase durations and flow control, which resulted in a fourfold extension of process duration until hollow fiber flow channel blockage occurred. Thus, the proposed concept appears to be superior to current cell retention devices in perfusion technology.

Effects of polysaccharides' molecular structure on membrane fouling and the related mechanisms.

Fouling behaviors of polysaccharides vary with their structure, while the mechanisms underlying this phenomenon remain unexplored. This work was carried out to explore the thermodynamic fouling mechanisms of polysaccharides with different structure. Carrageenan and xanthan gum were selected as the model polysaccharides with structure of straight and branch chains, respectively. Batch filtration experiments showed that xanthan gum solution corresponded to a more rapid flux decline trend, and specific filtration resistance (SFR) of xanthan gum (2.32 × 1015 m-1 kg-1) was over 10 times than that of carrageenan (2.21 × 1014 m-1 kg-1). It was found that, xanthan gum possessed a more disordered structure and a rather higher viscosity (15.03 mPa·s V.S. 1.98 mPa·s for carrageenan). Calculation of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed higher adhesion energy of xanthan gum (-42.82 my m-2 V.S. -23.26 mJ m-2 for carrageenan). Scanning electron microscopy (SEM) analyses showed that xanthan gum gel layer had a more homogenous structure and rigid polymer backbone, indicating better mixing with water to form a gel. As verified by heating experiments, such a structure tended to contain more bound water. According to this information, Flory-Huggins lattice theory was introduced to build a bridge between polymeric structure and SFR. It was revealed that branch structure corresponded to higher chemical potential change during gel layer formation, and higher ability to carry bound water, resulting in higher filtration resistance during filtration process. This work revealed the fundamental thermodynamic mechanism of membrane fouling caused by polysaccharides with different structure, deepening understanding of membrane fouling.

Production of nanoporous alumina membranes modified with multi‐walled carbon nanotube, polyacrylamide and polystyrene and use in wastewater treatment

AbstractIn this study, the nanofiltration materials having high selectivity, high filtration and mechanical resistance have been developed for the removal of organic contaminants in wastewater. Al2O3‐NP membranes were modified with multi‐walled carbon nanotube (MWCNT), polyacrylamide‐MWCNT (PA‐MWCNT) and polystyrene‐MWCNT (PS‐MWCNT) to provide better performance in the treatment of wastewater. The evaluation of the separation performance of the prepared membranes was carried out at 25°C using a vacuum filtration unit. Congo red (CR) and methylene blue (MB) dyes were selected as model pollutants. The results showed that the flux value was higher in the unmodified membrane, and the Al2O3‐NP membrane modified with MWCNT exhibited high removal efficiency among the modified membranes.

Application of hydrophilic modified nylon fabric membrane in an anammox-membrane bioreactor: performance and fouling characteristics.

The membrane fouling is the main bottleneck hindering the wide applications of anammox-membrane bioreactor (MBR). In this study, surface-coating hydrophilic modification of the membrane using polyvinyl alcohol was applied in a granular anammox-MBR. Stable anammox performance of >77% total nitrogen removal efficiency was achieved in both original and modified MBRs, along with decreasing anammox granule size. The modified membrane exhibited superior flux performance, and the membrane foulants were reduced in the MBR operation. Specifically, the foulant formation rate (f) was 0.46 g·m-2·d-1 for the modified membrane with 100-μm coating thickness (M100) compared with 0.75 g·m-2·d-1 for the original membrane (M0). However, the fouling cycle of the modified membrane with 250-μm coating thickness (M250) was greatly shortened (5 days compared with 19 days for M0) and f increased to 1.25 g·m-2·d-1. Specially, the excess adhesion of exopolysaccharides and humic substances to the hydrophilic modified membrane changed the fouling layer structure and filtration resistance distribution, ultimately causing higher filtration resistance when coating thickness increased. Notably, the flux decline contribution of the concentration polarization was only 33.3% for M0, while it was 71.3% for M250. Finally, it was revealed that using a modified membrane increased the biological secretion rate of polysaccharide but decreased the protein bio-production rate, leading to a high PS (polysaccharide)/PN (protein) ratio in the MBR. The fouling mechanism of the hydrophilic modified membrane applied in anammox-MBR was proposed, and we highlight that the degree of hydrophilic modification is crucial to mitigating membrane fouling.

Fouling behavior and mechanism of hydrophilic modified membrane in anammox membrane bioreactor: Role of gel layer

Membrane hydrophilic modification has been applied as an effective antifouling strategy for aerobic and anaerobic heterotrophic membrane bioreactors (MBRs), while its antifouling performance remains unclear for anaerobic ammonium oxidation (anammox) MBR. Herein, hydrophilic membranes (Mh) modified from pristine nylon fabric meshes (Mp, pore size of 20 μm), were applied in long-term operation of an anammox MBR. Although the average flux of Mh was 90.7% higher than that of Mp (p < 0.05) filtered with model foulant (bovine serum albumin) in a dead-end filtration test, the average filtration cycle of Mh in the anammox MBR was 37.9% shorter than that of Mp filtered with synthesized wastewater, in spite of the comparable total nitrogen removal efficiency (over 80%) achieved. A thin and compact gel layer was formed on Mh by adsorption of hydrophilic polysaccharide and further gelation of protein and colloidal biomass. The bound water wrapped in the gel layer on Mh brought about 32.8% higher filtration resistance, and caused 81.3% higher contribution rate of the flux decline caused by concentration polarization, compared with Mp. Moreover, more microbial metabolites, especially protein (23.9% vs. 17.7%), was rejected by Mh than Mp, providing organic matters for the proliferation of heterotrophic bacteria, and leading to the decreased relative abundance of anammox bacteria (from 63.2% to 35.2%). We proposed the formation process of the gel layer and revealed the membrane fouling mechanism on Mh in the anammox MBR, providing significant theoretical foundation for the membrane fouling control of anammox MBR systems.

The application of numerical simulation coupled flow and geomechanics in the study of geology-engineering integration

The low-permeability reservoir is mainly featured by small reservoir pore, tight, fine throat, high filtration resistance, and low oil productivity. After several years of working to recover hydrocarbons from these reservoirs effectively, it has been proven that creating complex fracture networks by multi-stage fracturing is one of the most efficient ways to enhance production. However, several factors affect the development of the complex fracture networks, and the in-situ stress is the most significant one. Low in-situ stress anisotropy [1] increases the possibility of creating complex fracture networks with hydraulic fracturing. In order to compensate for the in-situ stress anisotropy, based on the application of a numerical model coupled flow and geomechanics, this research analyzes the variation of in-situ stress and suggests arranging a sequence of horizontal well deployment. In addition, the research predicts the dynamic productivity coupled flow and geomechanics. From the results, this research concludes the dynamic change regularity of in-situ stress and the impact of difference well deployment, which is beneficial to optimize horizontal well deployment and fracturing design [2].

Study on dual-monomer melt-grafted poly(lactic acid) compatibilized poly(lactic acid)/polyamide 11 blends and toughened melt-blown nonwovens

With increasing demands on the high-performance and environmental-friendly melt-blown nonwovens (MBs) for separation and filtration, herein, we reported a poly(lactic acid)/polyamide 11 (PLA/PA11) 100% bio-based MBs in situ compatibilized by dual-monomer glycidyl methacrylate–styrene melt-grafted poly(lactic acid) (PLA-g-(St-co-GMA)). The morphology, crystallization, thermal and rheological behaviors of reactive extruded PLA/PA11/PLA-g-(St-co-GMA) melt blends were investigated, and the structure and filtration performance of corresponding MBs were fully characterized. The results indicated that the interface between PLA and PA11 were effectively improved due to the compatibilizer of PLA-g-(St-co-GMA). PA11 promoted the cold crystallization and enhanced the thermal stability of PLA matrix. The reactive blends displayed a higher viscosity with unchanged rheological behaviors compared with PLA. In comparison with PLA MBs, the average fiber diameter and pore size of PLA/PA11/PLA-g-(St-co-GMA) MBs were slightly increased, whereas the strength and toughness were significantly improved. All the PLA/PA11/PLA-g-(St-co-GMA) MBs presented high air permeability and low filtration resistance. High filtration efficiency (&gt;99.8%) could also be obtained especially for the target particles with diameters larger than 2.5 µm.

Membrane fouling in a membrane bioreactor: High filtration resistance of gel layer and its underlying mechanism

A membrane bioreactor (MBR) was continuously operated to investigate mechanisms of fouling caused by the gel layer in this study. Agar was used as a model foulant for gel layer formation, and filtration resistance of gel layers was systematically assessed. The results showed that gel layer possessed unusually high specific filtration resistance (SFR) and high measured porosity as compared with cake layer. Current knowledge cannot explain the contradiction between high filtration resistance and high porosity of gel layer. A new fouling mechanism based on Flory-Huggins theory was then proposed. Filtration resistance of agar gel layer was found to be independent of pH and ionic strength, but linearly increase with gel thickness. The results are accordant with the mechanism deductions. Simulation of the mechanism model showed that the filtration resistance induced by mixing chemical potential variation was comparable to the experimental data of filtration resistance of agar gel layer, indicating that the proposed mechanism is the predominant mechanism responsible for the high filtration resistance of gel layer. The proposed mechanism was further verified from the bound water viewpoint.

Filtration properties and skin formation of micro-crystalline cellulose

Solid–liquid filtration is an important unit operation used in several applications in the pulp and paper industry. It can be challenging especially for materials that forms filter cakes that has a tendency to be highly compressible. The formation of a skin, i.e. an initial cake with a considerably higher filtration resistance, can further increase the filtration resistance for these filter cakes. The separation process in these cases requires considerably larger filter areas.This study investigates skin formation during the filtration of micro-crystalline cellulose, examining the effect of the filter medium, filtration pressure and pH.Depending on the choice of filter medium, the average specific filtration resistance was found to vary by more than one order of magnitude. A decrease in the suspension pH from 6.3 to 2.9 lowered both the filtration resistance and the differences between the filtration media. Using local pressure profiles, a region of high filtration resistance for some of the filter media and pH values was identified close to the bottom of the filter cell. Characterisation of the media and micro-crystalline cellulose indicated that internal clogging of the filter medium was unlikely. This suggests that the filter cake closest to the filter medium had a considerably higher filtration resistance compared to the cake formed immediately after, i.e. a skin had been formed under certain conditions.

On the local filtration properties of microcrystalline cellulose during dead-end filtration

Dead-end filtration is frequently used in solid–liquid separation. In order to increase understanding of the filtration of materials that form compressible cakes, local filtration properties need to be taken into consideration. The compressible nature of these filter cakes requires phenomena such as skin formation, a dense layer of high filtration resistance close to the filter medium and flow stabilisation to be considered. This study investigates local filtration properties, i.e. the hydrostatic pressure and solidosity, in the dead-end filtration of microcrystalline cellulose, using slurries of varying pH levels and concentrations and two different filter media. The local measurements indicated that a dense skin was formed. This could be avoided when the nature of the particle–particle and particle–filter medium interactions was altered, using the pH to regulate the surface charge. Local filtration properties were used to find a critical material dependent Reynolds number indicating a flow stabilisation behaviour.

Investigation of the role of biopolymer clusters in MBR membrane fouling using flash freezing and environmental scanning electron microscopy

The technique that employs flash freezing and environmental scanning electron microscopy (ESEM) was utilised for detailed investigation of the fouling materials in a membrane bioreactor (MBR). The method involves the flash freezing of a wet sample in liquid nitrogen for 10 s to preserve its structure for direct ESEM observation with a high image resolution. ESEM images show that the sludge cake formed by simple filtration of the MBR bulk sludge has a highly porous, sponge-like structure with a fairly low resistance. However, the fouling layer attached to the membrane surface contains a thin gel layer under the main body of the sponge-like sludge cake, which is similar to that formed by filtration of a dispersion of biopolymer clusters (BPCs). It is apparent that BPCs tend to accumulate on the membrane surface, and the gel layer is largely responsible for the high filtration resistance of the cake layer on the fouled membranes.

The Role of Polysaccharide on the Filtration of Microbial Cells

The role of polysaccharide on the “dead-end” microfiltration of microbial cells is studied. Yeast and blue dextran are used as typical samples of microbial cells and polysaccharide, respectively. The filter cake becomes more compressible in the early periods of filtration and exhibits much higher filtration resistance when dextran molecules co-exist in the cake structure. A cake compression mechanism is proposed to explain the pressure effects on the cake structure and filtration resistance. For the two-component cakes, the dextran molecules deform easily even under a pressure as low as 30 kPa, while significant yeast deformation is observed when pressure is higher than 100 kPa. It is attributed to the depletion of most solid compressive pressures by deformed dextran molecules. The cake porosity data indicate that the cake compressibility is higher under low filtration pressure, and blue dextran plays a significant role on the cake structure and occupies a considerable volume in the cake. A resistance model is also derived for understanding the relationship between the average specific cake filtration resistance and filtration pressure. The cake filtration resistance is determined by the effective volume fraction of each component in cake and nearly the same as that of blue dextran under low pressure.

Effect of gel particle softness on the performance of cross-flow microfiltration

The gel particle softness effect on cross-flow microfiltration performance is studied. Three kinds of soft gel particles with a similar size distribution but different softness and compression behaviors were prepared and used in these experiments. The particle softness is the most important factor affecting the pseudo-steady filtration flux compared to the other operating variables in the conditions of this study. A filter cake formed by softer particles is compressed into a more compact structure, consequently, resulting in higher filtration resistance and lower filtration flux. The particle deposition probability is analyzed using a force balance model. An increase in particle softness leads to lower particle deposition probability as well as lighter cake mass due to the drastic flux decay. The cake compression during filtration is described using the Voigt in series model. The cake porosity suddenly decreases and the specific cake filtration resistance drastically increases in the early filtration period. The skin cake layer formation in that period plays the most important role in determining the cross-flow microfiltration performance. The cake mass and average specific filtration resistance calculation results using the proposed methods agree fairly with the available experimental data.

Improvement of arabinoxylan isolation from barley husks

A method of extracting arabinoxylan from barley husks has previously been developed, but was found to suffer from three problems, namely: starch was dispersed in the aqueous phase during steam pretreatment, the yield of extracted arabinoxylan with high molecular mass was low in the steam pretreatment step, and there was high filtration resistance in the clarification step. This paper presents possible solutions to these problems. Starch was removed prior to steam pretreatment by boiling the husks in water for 1 h. This treatment decreased the content of glucan in the aqueous phase after steam pretreatment by 75%. The yield of arabinoxylan with a molecular mass greater than 5 kDa was increased from 5% to 25% by using alkaline impregnation (1 wt.% NaOH). A vibrating shear-enhanced microfiltration unit was proven to be an alternative method to traditional filtration for clarification of the aqueous phase.

Membrane fouling in a submerged membrane bioreactor (SMBR): Characterisation of the sludge cake and its high filtration resistance

The attachment of sludge cake to the membrane surface is the main cause of the fouling problem in the submerged membrane bioreactors (SMBR) used in biological wastewater treatment. In this laboratory study, the sludge cake deposited on the membrane was found to have a specific filtration resistance of the order of 10 14 m/kg, which is much greater than expected for sludge cake formed during the dewatering of activated sludge. The filterability tests showed that the cake sludge removed from the fouled membrane of the SMBR had an average specific filtration resistance of 4.9 × 10 13 m/kg, whereas the sludge cake of the SMBR bulk sludge had an average filtration resistance of only 1.9 × 10 11 m/kg. Detailed chemical analysis showed there was a pool of biopolymer clusters (BPC) that was trapped within the sludge cake on the membrane. These clusters could be readily separated from the cake sludge by stirring it into a suspension. The abundance of non-filterable BPC as measured by the total organic carbon (TOC) in the suspended solids (SS) was about 10.3 mg/g SS for the cake sludge, in comparison to 0.4 mg/g SS for the bulk sludge. When the BPC were removed from the cake sludge, the filtration resistance of the cake sludge could be reduced considerably from 4.9 × 10 13 to 8.4 × 10 12 m/kg. It is argued that the BPC are a special form of organic matter formed by affinity clustering of the free extracellular polymeric substances (EPS) and soluble microbial products (SMP) in the sludge cake deposited on the membrane surface. The accumulation of BPC within the pores of the sludge cake is mostly responsible for the unusually high filtration resistance of the cake sludge during the SMBR operation.