Filtration Mode Research Articles

Reversibility of fouling on ultrafiltration membrane by backwashing and chemical cleaning: differences in organic fractions behaviour

Membrane fouling is an inherent phenomenon in ultrafiltration (UF) membrane processes, making it necessary to periodically perform backwashes (BW) and chemical “cleanings in place” (CIP) to restore the initial permeability of the membrane. The objective of this study was (1) to explore systematically the effect of distinct BW-related variables (BW transmembrane pressure, duration, frequency and composition) on the reversibility of UF membrane fouling and on the permeate quality (in terms of total organic carbon, turbidity and UV absorbance) over successive filtration/BW cycles; and (2) to identify which organic fractions were most removed by the membrane and, of these, which were most detached after BW, alkaline and oxidant CIP and acid CIP episodes. For this purpose, a bench-scale outside-in hollow fibre module operated under dead-end filtration mode at constant transmembrane pressure and treating settled water from a drinking water treatment plant was employed. Dissolved organic carbon fractionation was performed by high-performance size-exclusion chromatography. Results showed that, in general, the more intensive the BW was (in terms of high transmembrane pressure, shortened frequency and prolonged duration) the more effective it was in removing fouling from the membrane. Concerning the composition of the water used for the BW, the addition of NaClO led to maximum fouling reversibility, closely followed by the combination of NaOH + NaClO, while citric acid and NaOH contributed little compared to water alone. However, results also showed that irreversible fouling was never completely avoided whatever the BW regime applied, leading to a gradual increase in the total resistance over time. Larger differences in the behaviour of the different organic fractions were observed. UF membrane preferentially retained the heaviest fraction of biopolymers (BP), while the intermediate fraction of humic substances (HS) was removed at a lower percentage and the lighter fractions seemed to entirely pass through the UF membrane. The successive application of BW and CIPs resulted in the detachment from the membrane of a significant percentage of the retained BP, whereas only a modest percentage of the retained HS.

Size fractionation of elements and nanoparticles in natural water by both dead-end and tangential flow filtration

The influence of membrane filtration modes on the estimation of size distribution for natural elements in water was investigated. The stepwise membrane filtration is used to distinguish different size fractions including large particulate (>18 μm), particulate (0.2–18 μm), colloidal/nanoparticle (10 kDa–0.2 μm), and truly dissolved fractions (<10 kDa) in river water samples and wastewater treatment plants effluents. Dead-end and tangential flow filtrations were compared during fractionation process. For most elements, concentrations in different size fractions obtained by two filtration modes were generally similar. The obvious difference was only found in acid fractions for some elements, which might be related to the cake grown at membrane surfaces between two filtration modes. In case of elemental partitioning, the influence of filtration modes was normally negligible, when the membranes used and operational factors were exactly the same.

Shear-enhanced microfiltration of microalgae in a vibrating membrane module

The performance of a vibratory shear-enhanced membrane process for dewatering of freshwater microalgae, Chlorella vulgaris, has been studied. Chlorella vulgaris is a potential renewable feedstock for biofuel and bioproduct production. The efficient dewatering of the algal biomass is crucial for scale-up and sustainable design. This dynamic filtration system achieves high shear rates desirable for microfiltration by high-frequency torsional oscillations of the membrane unit. A 0.05 µm (nominal pore size) polyethersulfone microfiltration membrane was evaluated for the separation of suspended algae (0.5–100 g/L). The effect of process parameters such as trans-membrane pressure, surface shear rate, and solute concentration on permeate flux was evaluated and quantified. Algal biomass mixtures were dewatered with high algae rejections for all studies. The effect of trans-membrane pressure on permeate flux showed a classic pattern of a pressure-controlled region at lower pressures transforming to a mass transfer gel layer-controlled region at higher pressures, with quicker transitions at higher algae feed concentrations. The shear rate at the membrane surface was varied by changing the vibrational frequency of the unit. Permeate flux values observed in dynamic filtration mode, compared to those in cross-flow filtration (CFF) mode, were greater by a factor of 4.2–4.9. This process could provide a greener alternative to conventional mechanical and thermal separation systems, as high values of permeate flux and separation efficiency can be maintained with an energy consumption of 1.6 kWh/m3 of water removed.

Fouling control of a ceramic microfiltration membrane for direct sewer mining by backwashing with ozonated water

Backwashing using ozonated water was investigated to control fouling during direct sewer mining using a ceramic microfiltration (MF) membrane. Primarily treated municipal wastewater was filtered and backwashing was performed using RO filtered tap water in this study. Direct MF filtration in the dead-end filtration mode using the ceramic MF membrane resulted in fouling that could not be fully removed by conventional backwashing. A steady increase in transmembrane pressure (TMP) was observed after each filtration cycle and could be attributed mostly to cake formation. In contrast, backwashing using ozonated water for 2.5min was effective at removing the fouling cake layer; thus, resulting in a stable TMP value after multiple filtration cycles. The effectiveness of ozonated water backwashing could be enhanced by extending the backwashing time. Indeed, the permeability of a heavily fouled membrane was fully restored after 3.5min of ozonated water backwashing. Results reported here suggest that backwashing using ozonated water has the ability to remove most foulants deposited on the membrane surface and can be used for sewer mining, where severe cake formation occurs.

Energy filtration of secondary and backscattered electrons by the method of the retarding potential in scanning electron and ion microscopy

Data for the study of various contrasts in the methods of scanning electron and ion microscopy with the energy filtration of signals from secondary and reflected electrons are presented. A model of the formation of contrast by secondary electrons in a helium scanning electron microscope is formulated. The possibility of contrast amplification via energy filtration in a helium ion microscope as well as the chance of recording reflected ions by means of secondary electron detection is demonstrated. The recorded data for the material contrast in low-voltage electron microscopy at various acceleration voltages and different modes of energy filtration are given. The possibility of enhancing or reducing material contrast by means of energy filtration is shown.

Investigation of membrane fouling mechanisms using blocking models in the case of shear-enhanced ultrafiltration

Shear-enhanced ultrafiltration is considered as an important membrane technology that can contribute to pre-treat dairy wastewater and recycle valuable components such as milk proteins. However, to be efficient, it necessitates the establishment of proper methods for the assessment of membrane fouling. Four membrane blocking models proposed by Hermia were used to quantify and assess the membrane fouling of shear-enhanced filtration observed in dairy wastewater treatment. The experiments were performed with various shear rates, mean transmembrane pressure (TMP), temperature and membrane types. Good agreement between complete pore blocking model and experimental data was found, confirming the validity of the Hermia models for assessing the membrane fouling of shear-enhanced filtration system and that only some “sealing” of membrane pores occurs which is due to the high speed shearing effect. Furthermore, the increments of shear rate, TMP, and temperature can decrease the degree of “sealing” of membrane pores and improve filtration performance. In addition, a three-step membrane cleaning mode has achieved very satisfying results in subsequent membrane cleaning. This work confirms that, unlike traditional filtration mode (dead-end and cross flow filtration), high shear dynamic filtration possesses a low degree of membrane fouling and a higher membrane permeability recovery after cleaning.

Studding of Geo-Seepage Mode of Large Dams Foundations with Allowance Failure Antifiltering Elements

In this paper authors haveconsidered potentially possible causes of failures in filtration mode offoundation. Methods of calculated prediction of abnormal seepage processesparameters have been considered.

Development Geo-Seepage Models for Solving Seepage Problems of Large Dam’s Foundations, on an Example of ANSYS Mechanical APDL

In this paper authors have considered existing mathematical modeling methods of filtration mode of large dam’s foundations using finite element method. Practical analogies for solving filtration equation have been described concerning the problems of hydraulic engineering. Recommendations for solution to filtration problems have been given based on use of general-purpose industrial CAE software.

Retention of modified BSA by ultrafiltration membranes

AbstractBACKGROUNDThe efficiency of protein purification depends on membrane pore size and electrostatic repulsion between a protein and membrane surface. The current study investigates how deliberate protein modification affects the electrostatic repulsion, degree of protein separation and transmembrane flux.RESULTSThe experiments were performed with bovine serum albumin (BSA) modified by guanidation, succinylation and citraconation. The latter modification is reversible and can be used to improve the protein separation. Modified and native proteins were filtrated through polyethersulphone PES‐20 membrane in dead‐end and cross‐flow filtration modes at pH 5–10. Guanidation diminished electronegativity of the protein. In dead‐end mode, the relative flux in separation of modified BSA decreased to 0.45–0.7 of the flux of pure water over 27.5 min. In the case of unmodified BSA, the average relative flux drop was 0.3–0.5. The separation of guanidated BSA increased on average by 11% in acidic conditions. Succinylation and citraconation increased BSA electronegativity. The average flux remained close to the flux of pure water declining by 0.2–0.4, and the separation was greater than 95% at alkaline conditions in both dead‐end and cross‐flow operational modes.CONCLUSIONSuggested modifications do not require changes in chemistry of bulk suspensions and membranes, but do increase protein rejection keeping high transmembrane flux. The suggested approach is novel and holds the promise of achieving the purity level of therapeutic proteins required by drug authorities. Under the conditions investigated the best results were observed for succinylation and filtration in cross‐flow mode at pH 5–10. © 2014 Society of Chemical Industry

Basic regularities of the filtration drying of wheat grain

This paper discusses the results of experimental investigations into the hydrodynamics and heat exchange specific to the filtration drying of wheat grain. The result of experimental investigations into the hydrodynamics has been generalized based on the inner problem, exterior problem and a mixed problem of hydrodynamics. The experimental data representations in the form of dimensionless numbers are easy-to-use in practice and enable determine the energy cost and the economic feasibility of the process. Determining the optimal parameters of filtration drying process was ensure by the investigation into heat exchange specificities and their generalization in the form of dimensionless numbers that would enable to compute the heat rejection factors, with the filtration modes and physical parameters of the heating medium being known. Obtained are the design dependences to determine the internal diffusion coefficients against the temperature of a heating medium and the initial moisture content of grains. The resulting design dependency may be used to predict the duration of the wheat grain filtration drying. Determined are the rational modes of drying for seed grain and food grain.

Effect of various sonication modes on permeation flux in cross flow ultrafiltration membrane

The effects of different sonication modes with different frequencies of ultrasound on permeation flux and fouling of ultrafiltration membrane were investigated. The flat sheet membranes in cross flow ultrafiltration were irradiated using various frequencies (37, 80KHz and tandem) in different sonication modes (continuous, pulsed, sweeping, and degassing). The results showed that the permeation flux was increased with decreasing of ultrasound frequencies. Among applied irradiation modes, the pulsed mode had the most effect on enhancement of permeation flux and reduction of fouling percentage and fouling ratio factor. Creating alternative mode by power intensity changings was more effective than frequency changings. In best condition of filtration, 37KHz and pulsed mode, the fouling percentage and sonication effect factor (SEF), were 10.53, and 187.4%, respectively. Also permeation flux of pure water confirmed the ultrasonic assisted separation method had no destructive effects on membrane.

The effect of permeation flux on the specific resistance of polysaccharide fouling layers developing during dead-end ultrafiltration

Development of polysaccharide fouling layers during dead-end membrane ultrafiltration is an inherent problem in water treatment and similar separation processes. Despite its practical significance, ultrafiltration membrane fouling under constant permeate flux J has received inadequate attention. Therefore, constant-flux experiments, with typical alginate model-solutions covering the flux range of practical interest (i.e. 10–100L/m2h), are employed to obtain new insights into fouling layer characteristics. The specific resistance α, as the most representative fouling-layer property, is used for data interpretation. The behavior of resistance α, with increasing permeate volume, confirms that these gel-type layers are strongly affected by flux J and generally compressible. Layer compressibility is evident beyond an initial phase of membrane coverage by alginates. The initial resistance αi, corresponding to thin developing layers and relatively small pressure-drop across the layer/“cake” ΔPc, is independent of ΔPc, approximately linearly increasing with J. For all data-sets, variation of resistance α with ΔPc is well correlated by a generalized expression involving (in addition to αi) two parameters, n and Pa, considered to represent layer/cake compressibility index and reference pressure, respectively; these parameters also increase (and are fairly well correlated) with J. The usefulness of these data is demonstrated in elucidating issues such as "critical flux" for this filtration mode.

Исследование фильтрационного режима оснований высоких плотин на математических моделях

Исследование фильтрационного режима оснований высоких плотин на математических моделях

Effects of filtration modes on membrane fouling behavior and treatment in submerged membrane bioreactor

Relaxation or backwashing is obligatory for effective operation of membrane module and intermittent aeration is helpful for nutrients removal. This study was performed to investigate effects of different filtration modes on membrane fouling behavior and treatment in membrane bioreactor (MBR) operated at three modes i.e., 12, 10 and 8min filtration and 3, 2, and 2min relaxation corresponding to 6, 5 and 4cycles/hour, respectively. Various parameters including trans-membrane pressure, specific cake resistance, specific oxygen uptake rate, nutrients removal and sludge dewaterability were examined to optimize the filtration mode. TMP profiles showed that MBR(8+2) with 8min filtration and 2min relaxation reduced the fouling rate and depicted long filtration time in MBR treating synthetic wastewater. MBR(12+3) was more efficient in organic and nutrients removal while denitrification rate was high in MBR(8+2).

Purification and Concentration of Caustic Mercerization Wastewater by Membrane Processes and Evaporation for Reuse

A membrane-based treatment strategy was developed for purifying the highly alkaline textile mercerization wastewater. 0.2-μm MF and 100 kDa UF membranes were evaluated as pretreatment alternatives before 10 kDa UF and 200 Da NF membranes. Turbidity was almost totally removed by both pretreatment options, while UF (100 kDa) showed higher COD retention than MF. In total recycle mode of filtration, fouling of both UF and MF membranes were 80% reversible by physical and almost totally reversible (≥ 97%) by chemical cleaning. In the second stage filtrations applied to the pretreated wastewater samples, NF could yield high (97-98%) COD retentions and low permeate COD concentrations (≤ 22 mg/L), while 10 kDa UF could only reduce the COD concentration to 150 mg/L. While no NaOH was lost in the MF+UF process, the use of NF as second stage resulted in 12-17% NaOH retention. The permeate flux in all second stage processes were stable, implying that the majority of the feed components that would cause fouling had been removed in the pretreatment stages. Permeate of the MF+NF sequence was concentrated by evaporation with no foaming problems, showing that the hybrid process can be applied to recycle a purified and concentrated caustic stream to the mercerization process.

Effect of granular activated carbon addition on the effluent properties and fouling potentials of membrane-coupled expanded granular sludge bed process

To mitigate membrane fouling of membrane-coupled anaerobic process, granular activated carbon (GAC: 50g/L) was added into an expanded granular sludge bed (EGSB). A short-term ultrafiltration test was investigated for analyzing membrane fouling potential and underlying fouling mechanisms. The results showed that adding GAC into the EGSB not only improved the COD removal efficiency, but also alleviated membrane fouling efficiently because GAC could help to reduce soluble microbial products, polysaccharides and proteins by 26.8%, 27.8% and 24.7%, respectively, compared with the control system. Furthermore, excitation emission matrix (EEM) fluorescence spectroscopy analysis revealed that GAC addition mainly reduced tryptophan protein-like, aromatic protein-like and fulvic-like substances. In addition, the resistance distribution analysis demonstrated that adding GAC primarily decreased the cake layer resistance by 53.5%. The classic filtration mode analysis showed that cake filtration was the major fouling mechanism for membrane-coupled EGSB process regardless of the GAC addition.

Assessment of solvent resistant nanofiltration membranes for valorization of deodorizer distillates

The valorization of deodorizer distillates from the oil refining industry requires a stable membrane suitable to separate steryl esters (bioactive compounds with high molecular weight (MW), 650<MW<800g/mol) from pesticides (150<MW<400g/mol), whose content is restricted by the actual legislation. This work aims at identifying a suitable solvent and a solvent resistant nanofiltration (SRNF) membrane to be used in a diananofiltration process for the removal of pesticides.Hexane, ethanol and oleic acid were investigated as potential solvents. The role of solvent–membrane interactions was found to be important in the permeability of the membrane, supported by a strong relationship with the swelling/solvent viscosity ratio. Selected membranes were compared in a dead-end filtration mode, which allowed for identifying the membrane(s) that showed the best compromise between permeability and discrimination between the target compounds. The membranes with the best performance were GMT-oNF2 from Borsig/GMT, PuraMemS600 from Evonik and 030306F from Solsep. The performance of the process was enhanced while operating in a cross-flow mode, being further improved after optimization of the concentration of deodorizer distillate and of the processing solutions and the transmembrane pressure.The membranes identified in this work proved to be suitable for valorization of deodorizer distillates, presenting high rejections of steryl esters (>96%) and significant low rejection of pesticides (<65%), under optimised conditions.

Investigation of geometric properties of media particles and operating conditions on floating media filtration

Filtration is an effective process in removing particles that are present in water. Floating medium filter has been used in direct filtration because of its flexibility, cost savings gained by less land requirements, and less water and energy required for backwashing. The aim of this work was to investigate the effect of geometric properties of a floating medium in upflow filtration mode. A pilot plant was designed and constructed to evaluate the filtration process. Effect of physical parameters on filtration performance was also investigated. The experiments were carried out using a commonly available polypropylene floating medium. Four median grain sizes (2.28, 3.03, 3.30, and 4.07 mm) of polypropylene plastic pellets were used. Two media shapes (cubic and disc) were evaluated. Bentonite (250 mg/L ≈ 60 NTU) was used to make up the raw feed water. Three parameters that could influence the filtration performance were identified, namely: filtration velocity, media depth, and coagulant dose. The results showed that the best conditions to remove turbidity were found to be: low filtration rate (36.8 L/m2 min), longer media depth (600 mm) and optimum coagulant dose (23 mg/L). The results also indicated that the smaller plastic medium (2.28 mm) was more efficient in terms of turbidity removal than the larger medium. However, headloss development associated with smaller media was higher (109 mm of water) than that associated with larger medium (42 mm of water).

A triple fouling layers perspective on evaluation of membrane fouling under different scenarios of membrane bioreactor operation.

One of the main factors affecting membrane fouling in MBRs is operational conditions. In this study the influence of aeration rate, filtration mode, and SRT on hollow fiber membrane fouling was investigated using a triple fouling layers perspective. The sludge microbial population distribution was also determined by PCR method. Through various applied operational scenarios the optimal conditions were: aeration rate of 15 LPM; relaxation mode with 40s duration and 8 min. interval; and SRT of 30 days. The similarity between SMP variations in triple fouling layers with its corresponding hydraulic resistance confirmed the effect of SMP on membrane fouling. Among three fouling fractions, the upper (rinsed) layer found to have the most effect on membrane fouling which implies the critical role of aeration, but as for multilateral effects of aeration, the optimal aeration rate should be determined more precisely. Relaxation interval was more effective than its duration for fouling control. SRT variations in addition to influencing the amount of SMP, also affect on the structure of these material. At longer SRTs (20, 30 days) a greater percentage of SMP could penetrate into the membrane pores and for shorter SRTs they accumulate more on membrane surface. Results showed that there is a very good correlation between total hydraulic resistance (Log R) and protein to carbohydrate ratio at the rinsed layer (P1/C1). Considering significant effects of aeration and SRT conditions on this ratio (according to data), it is very determinative to apply the optimal aeration and SRT conditions.

The effect of NaCl on the adsorption of human IgG onto CM-Asp–PEVA hollow fiber membrane-immobilized nickel and cobalt metal ions

Over the past decade, immobilized metal-affinity adsorbents have attracted increasing interest for purification of natural and recombinant immunoglobulin G (IgG). In this work, nickel and cobalt metal ions complexed with CM-Asp (carboxymethylaspartate) immobilized on poly(ethylenevinyl alcohol) (PEVA) hollow fiber membranes were evaluated for purification of human IgG from serum. The buffer system and NaCl had important effects on human serum protein adsorption in both adsorbents. Efficient purification of IgG was accomplished in sodium phosphate buffer without NaCl at pH 7.0. Under this condition, the electrostatic interactions are important for adsorption. The Ni(II)-CM-Asp–PEVA had a protein adsorption capacity of 17.5 mg of IgG mL−1 fiber when human serum diluted was loaded in crossflow filtration mode and the eluted IgG had a purity of 82.6 % (based on total protein and IgG, IgM, HSA, and Trf nephelometric analysis). Fitting the experimental IgG adsorption data to the Langmuir and Langmuir–Freundlich models showed that Ni(II)-CM-Asp and Co(II)-CM-Asp had Langmuirean and non-Langmuirean behavior, respectively, with positive cooperativity for IgG-Co(II)-CM-Asp binding, probably due to multipoint interactions (n = 2.12 ± 0.31). Thus, these membranes can be considered as alternative adsorbents for the purification or depletion of IgG from human serum.