Internal Fouling Research Articles

The effect of apple cider characteristics and membrane pore size on membrane fouling

Microfiltration (MF) of apple cider using four membrane pore sizes was investigated. MF with 0.2 and 0.45 μm pore sizes, and with 0.8 and 1.4 μm pore sizes, respectively, resulted in similar flux behavior and MF juice characteristics. Clear juice was obtained using all four pore sizes. MF did not cause any significant changes in pH and °Brix, regardless of pore size. Viscosity of the MF juice was lower than of the unfiltered apple cider for all membranes, but the viscosity decrease was the largest for the 0.2 and 0.45 μm membranes, due to the low transmission of pectin into the MF juice. Pectin transmission was 3–9% of the initial pectin content for the 0.2 μm membrane, 6–51% for the 0.45 μm. 45–100% for the 0.8 μm, and 60–100% for the 1.4 μm membrane. Apple cider haze particles that were smaller or of size comparable with the membrane pore size were deemed responsible for fouling, while particles much larger than the pores did not have a significant contribution to fouling. The fouling of 0.2 μm and 0.45 μm membranes was dominated by cake layer formation (external fouling), while fouling of the 0.8 μm and 1.4 μm membranes was dominated by pore constriction and pore blocking (internal fouling).

Analysis of backwashing efficiency in dead-end hollow-fibre ultrafiltration of anaerobic suspensions.

A novel dead-end mode operation for filtering anaerobic suspensions was investigated. In this mode, the filtration system automatically adjusted backwashing frequency to a preselected transmembrane pressure set-point. This paper discusses the effectiveness of the backwashing conditions on membrane fouling. Anaerobic suspensions from a conventional wastewater treatment plant digester were used as model suspensions for the trials carried out at lab-scale. Gas sparging aided backwashing significantly enhanced membrane cleaning efficiency. No effect of gas sparging on internal fouling was detected. Also, the cleaning efficiency linearly decreased with permeate flux. Nevertheless, due to a high increase in the reversible fouling, a reasonable net permeate flux (7.2-6.8 L/h m(2)) can be achieved when intermediate fluxes (12-16 L/h m(2)) were imposed and the higher transmembrane pressure set-point value (50 kPa) was applied. Both backwashing duration and flux exhibited similar influence on cake fouling removal for a given volume of permeate produced.

Hydraulically irreversible fouling on ceramic MF/UF membranes: Comparison of fouling indices, foulant composition and irreversible pore narrowing

The application of ceramic membranes in water treatment is becoming increasing attractive because of their long life time and excellent chemical, mechanical and thermal stability. However, fouling of ceramic membranes, especially hydraulically irreversible fouling, is still a critical aspect affecting the operational cost and energy consumption in water treatment plants. In this study, four ceramic membranes with pore sizes or molecular weight cut-off (MWCO) of 0.20μm, 0.14μm, 300kDa and 50kDa were compared during natural surface water filtration with respect to hydraulically irreversible fouling index (HIFI), foulant composition and narrowing of pore size due to the irreversible fouling. Our results showed that the hydraulically irreversible fouling index (HIFI) was proportional to the membrane pore size (r2=0.89) when the same feed water was filtrated. The UF membranes showed lower HIFI values than the MF membranes. Pore narrowing (internal fouling) was found to be a main fouling pattern of the hydraulically irreversible fouling. The internal fouling was caused by monolayer adsorption of foulants with different sizes that is dependent on the size of the membrane pore.

Effects of Continuous Pollution by Pharmaceutical Micropollutants on the Fouling of a Membrane Bioreactor Treating Domestic Wastewater

Membrane bioreactors (MBR) are increasingly used for domestic wastewater treatment and reuse and great concerns have been raised in the last decade about some emerging trace pollutants found in aquatic environment, notably pharmaceutical products. As a consequence, the removal of pharmaceutical micropollutants by MBRs has been extensively investigated but there is still a lack of knowledge on the effects of the current presence of pharmaceutical micropollutants in domestic wastewaters on MBR fouling. Among the different pharmaceuticals, it was decided to focus on carbamazepine (CBZ), an anti-epileptic drug, because of its occurrence in domestic wastewaters and persistence in biological processes including MBRs. The chemical analysis of soluble microbial products (SMPs) in the supernatant showed that a continuous introduction of CBZ into a submerged MBR via the feed (about 90 µg/L CBZ in the feed) led to a significant increase in the concentration of proteins whereas no significant change was found for polysaccharides. Size exclusion high performance liquid chromatography (HPLC-SEC) analysis showed that the addition of CBZ induced a significant increase of 10-100 kDa proteins in the supernatant and a slight decrease of 100-1000 kDa proteins. After addition of CBZ a significant increase of transmembrane pressure (TMP) in the MBR was observed, which indicates that the increase of the quantity of 10-100 kDa proteins led to a more severe fouling caused by internal fouling in the biocake that was formed on MBR membrane surface. This study also suggests that 10-100 kDa proteins might play a major role in the TMP jump phenomenon. Moreover it was found that addition of CBZ to the MBR affected the biological activities, as a slight inhibition of the exogenous respiration rate was observed.

Contributions of Internal and External Fouling to Transmembrane Pressure in MBRs: Experiments and Modeling

AbstractThis paper reports a new approach to understanding membrane fouling in membrane bioreactors (MBR). The foulants were categorized into those inside the membrane (internal fouling) and those on the membrane forming the so-called external fouling layer (external fouling). The volumes of the internal and external foulants were determined with the aid of a confocal laser scanning microscope (CLSM) after staining the foulants. Thus, the porosities of both the membrane and the external fouling layer were calculated, which explained the contributions of internal and external fouling to transmembrane pressure (TMP) from the standpoint of fundamental filtration theory. The categorical method indicates that external fouling may dominate the long-term operation of MBR with the formation of the external fouling layer, whereas internal fouling, in the form of pore constriction, may cause both initial and final TMP jumps under the operating conditions in the current study. In addition, a mathematical model was d...

Pressure retarded osmosis for osmotic power production: influence of internal concentration polarization and membrane fouling

Pressure retarded osmosis for osmotic power production: influence of internal concentration polarization and membrane fouling

Structure and properties of PVDF membrane with PES-C addition via thermally induced phase separation process

Polyvinylidene fluoride (PVDF) membrane and PVDF membrane with phenolphthalein polyethersulfone (PES-C) addition were prepared via thermally induced phase separation (TIPS) method by using diphenyl carbonate (DPC) and dimethyl acetamide (DMAc) as mixed diluents. The effects of coagulation temperature and pre-evaporation time on structure and properties of membranes were studied. The changes of sewage flux in MBR and the attenuation coefficient of sewage flux were investigated. The resistance distributions of PVDF and PVDF/PES-C membranes were compared by resistance analysis. Membrane composition and structure were characterized by ATR-FTIR, TGA, SEM and AFM. The foulant on membranes was analyzed by FTIR. The contact angle of PVDF/PES-C membrane was lower than that of PVDF membrane. A thinner skin layer and a porous cellular support layer formed in PVDF/PES-C membrane and resulted in a higher porosity and pure water flux. The pure water flux and porosity of PVDF/PES-C membrane increased with rising coagulation temperature and decreased with extending pre-evaporation time. The flux attenuation coefficient, the cake layer resistance and internal fouling resistance of PVDF/PES-C membrane in MBR were smaller than those of PVDF membrane in MBR. The FTIR spectrum of foulant on membrane indicated that the foulant on PVDF/PES-C membrane was mostly composed of protein and polysaccharide, while the foulant on pure PVDF membrane included biopolymer clusters besides protein and polysaccharide.

Application of Fe(II)/K2MnO4 as a pre-treatment for controlling UF membrane fouling in drinking water treatment

This paper describes some results of mini-pilot-scale tests concerning the performance of potassium manganate (K2MnO4) as a pre-treatment chemical prior to ultrafiltration. Manganate is an intermediate in the commercial preparation of permanganate and in aqueous reactions MnO42− can act as both an oxidant and a coagulant/adsorbent arising from the formation of insoluble MnO2. In addition, the combination of ferrous sulfate and manganate (Fe/Mn), offers a potentially cheaper and effective combination of pre-oxidant and coagulant compared to the chemicals used currently in water treatment (e.g. ozone, chlorine, ferric sulfate). In comparative tests with conventional ferric sulfate and using simulated raw water, the results showed that Fe/Mn pre-treatment substantially reduced membrane fouling in terms of the rate of trans-membrane pressure development (arising from both external and internal fouling). Fe/Mn pre-treatment was effective in reducing bacterial activity, changing the characteristics of organic matter and decreasing the production of extracellular polymeric substances (EPS) by bacteria. The external fouling in this process was determined by the EPS concentration, and the internal fouling mainly determined by the adsorption of lower MW organic matter to the membrane pores. Fe/Mn pre-treatment reduced the amounts of both types of fouling material within the cake layer and membrane pores in comparison to conventional pre-treatment with ferrous sulfate, most likely through the formation of solid-phase Fe(III) and MnO2 and by MnO42− oxidation, thereby leading to a substantial increase in membrane run time.

Characterization of ultrafiltration membranes fouled by quantum dots by confocal laser scanning microscopy

The extensive applications of engineered nanomaterials (ENMs) can result in their release into waters. Membrane processes have great potential in reducing ENMs release. In that case, the issues of particular concern are membrane fouling caused by ENMs during separation processes. The objective of the present study is to improve the understanding of how ENMs are retained by membranes. An innovative methodology using confocal laser scanning microscopy (CSLM) is developed to locate fluorescent CdTe quantum dots (QDs) in different depths of fouled ultrafiltration membranes. With the help of image analysis software, both qualitative and quantitative information about the distribution of QDs in membranes are obtained. For low molecular weight cut off (MWCO) membranes (1, 5 and 10kDa), QDs (sizes from 1 to 5nm) distributed mainly around surfaces or on top of membranes, accompanied with near 100% retention regardless of transmembrane pressure. As membrane MWCO increased (30 and 100kDa), more QDs could pass through membranes accompanied with decreasing retention efficiencies and the occurrence of QDs was usually in deeper positions of membranes. Distribution results were in agreement with fouling analysis which demonstrated that standard blocking (internal fouling) and/or cake models (external fouling) frequently occurred during filtrations of QDs.

Investigation of Consecutive Fouling and Cleaning Cycles of Ultrafiltration Membranes Used for Whey Processing

Abstract Development of resistance during multiple foulings and three-step Cleaning-In-Place (CIP) operations, simulating an industrial cleaning regime of polysulfone ultrafiltration membranes, was investigated. The study explored how trans-membrane pressure (150 and 300 kPa) and feed protein concentration (0.9 and 10%) influenced resistance reduction during filtration and flux recovery by the cleaning procedures. New membranes, pre-cleaned with a full CIP cycle, were used for each experiment. Subsequent fouling (simulating production) and CIP were done three times in a row and the development of fouling layer resistance was monitored and evaluated. Results show that filtration performance decreased during the first days of usage, possibly related to build-up of internal fouling. Cleaning success based on flux recovery was negatively influenced by a high protein concentration in the feed, but independent of the trans-membrane pressure during filtration.

Fouling mechanisms of Pseudomonas putida on PES microfiltration membranes

The mechanisms by which Pseudomonas putida causes fouling on a microfiltration membrane have been studied. For an initial P. putida concentration of 0.77g/L (5.1×108cfu/mL) stirred dead-end tests indicated that approximately 70% of the permeability was lost during the first minute of filtration and only 15% more was lost during the following 24min. SEM observations showed the presence of aggregates within the most external part of the membrane pores, partially blocking these pores and leading to more or less regular surface deposits and consequently, an intermediate blocking model was proposed and successfully fitted. The analysis of fouling resistance-in-series indicated that the selection of a high TMP during the microfiltration of P. putida had no effect on the final permeate flux but provoked an increase in external in comparison to internal fouling. On the other hand, the selection of a lower TMP led to a low rate of accumulation of P. putida on the membrane, reducing the total membrane resistance and allowing a deeper penetration of the bacteria into the pore. Studies on the cleanability of the membrane using sonication showed how this technique was more effective when membrane was fouled at higher TMP, achieving permeability recoveries of around 80% in the best cases.

Direct Visualization of Fouling Inside a Hollow-Fiber Ultrafiltration Membrane Caused by Sodium Alginate

Sodium alginate (SA), known as a type of polysaccharide, was one of the main foulants in a water ultrafiltration (UF) system. In this study, internal membrane fouling of rhodamine-labeled SA filtration through polyethersulfone (PES) UF hollow-fiber membranes was directly observed using fluorescent microscopy. Different molecular weight cut-offs (MWCOs) and morphologies of PES membranes resulted in different internal accumulation of SA in membranes. Fluorescent microscope images showed that SA molecules tended to accumulate at the vacant spaces inside membranes without forming a foulant layer on membrane surfaces during filtration. SA that accumulated at the vacant spaces was removed by backwashing. Filtration types (inner-pressured and outer-pressured) also affected internal fouling of SA due to asymmetric structures of PES membranes, regardless of the similar flux and rejection results between the filtration types. Understanding internal fouling provides important insights into membrane fouling and useful information for the rational design of a filtration system using a hollow-fiber membrane.

A new strategy for ultralow biofouling membranes: Uniform and ultrathin hydrophilic coatings using liquid carbon dioxide

Highly stable, uniform and ultrathin hydrophilic polymer coatings on the surface as well as in the pores of a PVDF microfiltration (MF) membrane are obtained by coating a hydrophilic monomer in liquid carbon dioxide (l-CO2) followed by subsequent crosslinking reaction. Polyethylene glycol diacrylate (PEGDA, Mn ~258g/mol) is used as the l-CO2 soluble hydrophilic monomer source and azobisisobutyronitrile (AIBN) was used as a radical initiator. The extremely low surface tension and the low viscosity of l-CO2 result in ultrathin and uniform PEG coatings on the hydrophobic polyvinylidene fluoride (PVDF) microfiltration membrane. The chemical composition, morphology, and the depth profiles of the PEG-coated membranes are characterized in detail using X-ray photoelectron spectroscopy, scanning electron microscopy, electron probe microanalysis and energy dispersive X-ray microanalysis. Long-term permeation flux test using a bovine serum albumin solution shows that the 1.0wt% PEGDA-coated membrane using l-CO2 exhibits 1.34 times larger BSA solution flux than that of the uncoated PVDF membrane, and 1.3 times larger flux than that of a commercial hydrophilic membrane. Fouling resistance estimation shows that the 1wt% PEGDA-coated membrane exhibits ~30% lower internal fouling resistance than the pristine membrane, and ~24% lower internal fouling resistance than the commercial hydrophilic membrane.

Influence of crossflow microfiltration on ceramic membrane fouling and beer quality

In this article, an experimental investigation has been carried out to determine the types of fouling phenomena that occur during clarification of dilute malt extract (DME) and pasteurization of clarified beer (CB) by a tubular ceramic membrane in a crossflow pilot plant. Using the classical models, the predominant fouling mechanism responsible for flux decline was found to be complete blocking of the membrane pores followed by formation of a compressible cake layer of yeast cell in the case of DME clarification, whereas the internal fouling of the membrane occurs during pasteurization of CB. The effects of operating parameters, including temperature, transmembrane pressure, and crossflow velocity, on the steady-state permeate flux, as the key factor of crossflow microfiltration processes, were examined. For CB microfiltration, the steady-state permeation flux increased almost linearly with transmembrane pressure and the membrane could reduce the turbidity by 60%. For DME filtration, the maximum value of permeation flux (20 LMH) was obtained under medium transmembrane pressure of 1.1 bar and the highest crossflow velocity. The filtered beer quality parameters, such as haze, color, proteins, polyphenols and bitterness, were examined after 8 h of filtration to ensure the transmission of beer compounds that are essential for beer quality. The results of quality analysis showed that the ceramic membrane crossflow filtration, regardless of very low permeation flux, appears to be a reliable substitution for the traditional Kieselguhr filtration in beer clarification.

Application of filtration blocking models to describe fouling and transmission of large plasmids DNA in sterile filtration

Sterile filtration is considered as a final step in processing pharmaceutical grade plasmid DNA. During the development of the filtration process, fundamental understanding on the mechanism of fouling is critical to improve filtration operations. The mechanism of fouling of pQR150 (20kb) and pGEc47 (56kb) plasmids DNA during constant pressure filtration inside 0.22μm PVDF membrane is experimentally investigated. The decline of filtrate flux as a function of time is analysed using the framework of classical and combined blocking models. The results for both plasmids indicate a transition between fouling mechanisms. Initially, during the early part of the filtration, the intermediate blocking model provided the best fit of the experimental results suggesting that fouling of the membrane was mainly caused by deposition of particles onto its surface. Afterwards, the result trends were best captured by the standard blocking model indicating that internal fouling of the membrane was the dominant fouling mechanism. A study of the transmission of both plasmids shows a significant reduction of plasmid transmission which coincides with the transition of the fouling mechanism from intermediate to standard blocking. The study highlights how the fouling behaviour of large plasmid DNA during sterile filtration is determined by the complex interplay between the flexibility of the molecules and the internal structure of the membrane.

Assessment of fouling-resistant membranes for additive-free treatment of high-strength wastewaters

In this contribution, we investigate the use of fouling-resistant and cleanable membranes designed for treatment of oily water in the treatment of high-strength industrial wastewaters that present challenges to classical treatment technologies. Membrane surfaces were characterized by spectroscopy and electron microscopy pre- and post-filtration to determine the extent of fouling. Low molecular weight cutoff membranes showed stable permeate fluxes without the need for intermittent cleaning, characteristic of systems with low degrees of internal fouling. For 100kDa molecular weight cutoff membranes, flux decline was more severe. While polymer-modified membranes processed ~26% more permeate than the unmodified membranes in this case, flux recovery after a membrane cleaning step was low and similar for the unmodified and modified membranes, characteristic of high degrees of internal fouling. All membranes reduced turbidity nearly 100% and chemical oxygen demand was reduced 70–84%. These results indicate that ‘tight’ ultrafiltration membranes designed for treatment of oily waters can be used for primary treatment of other highly impaired wastewaters, and the use of more ‘open’ ultrafiltration membranes will require further development and optimization of cleaning protocols.

Characteristics of flux and gel layer on microfilter and non-woven fabric filter surface based on anoxic–aerobic MBRs

Non-woven fabric filter- (NWFF) and microfilter-MBR modules were made using 100μm polypropylene and 0.25μm polyethylene materials, respectively. The performances and mechanisms of the two processes were investigated, including additional batch filtration tests to find the function of the dynamic gel layer on the membrane surface. The HRT of both MBRs was 9h and the operating permeate flux was 13L/m(2)/h. The two MBRs consisted of an anoxic and aerobic reactor. The NWFF or microfilter (MF) was submerged in each of the aerobic reactors. The two MBRs showed similar performances for the removal of organic matters, suspended solids and nitrogen. Cake formation on the NWFF contributed to major resistance, while the gel layer on the microfilter or internal fouling of the pores played a key role in the fouling of the membrane surface. The amount of soluble extracellular polymer substances (EPS) (13mg/L) of the attached sludge on the NWFF surface was larger than that (11mg/L) of that suspended sludge. Consequently, the functional gel layer for the coarse and microfilter is established based on the relationship among the EPS, transmembrane pressure and MLSS.

Surfactant cleaning of UF membranes fouled by proteins

Surfactant cleaning of ultrafiltration membranes is essentially a sequence of three stages. The micelles, formed when the dose of nonionic surfactant exceeds the critical micelle concentration, transport to the membrane surface, partially disassemble, and bind to proteins. The binding first results in protein dislocation but then continues to surfactant occupation of the membrane surface including the sites released by the proteins. The membrane surface gradually becomes more hydrophilic and ripe for the adsorption of micelles that now build a cake layer. The developed cake is responsible for an increased protein retention and severe fouling.The surfactant cleaning time needs to be optimized to maximize the protein solubilization and to prevent the growth of a micelle cake. Circulation of a cleaning solution accelerates the surfactant transport to the membrane surface but facilitates micelle pore blocking. The induced internal fouling can counteract the benefits of reduced cleaning times due to circulation. Water flow can disassemble the external cake and wash away surfactant monomers, but will barely release clogged pores.

Fouling with aerobic granule membrane bioreactor

Aerobic granulation (AG) and membrane bioreactor (MBR) are two promising, novel environmental biotechnological processes that draw interest of researchers working in the area of biological wastewater treatment. Membrane fouling in the combined aerobic granular membrane bioreactor (AGMBR) process and the conventional MBR process was investigated in this work. The irreversible fouling on hollow-fibre membranes in both reactors were observed with the multiple staining and confocal laser scanning microscope technique. Following physical and chemical washing, the external fouling layers were mostly removed. However, the biofilms built up in the interior surface of membrane remained and contributed to the irreversible fouling resistance. AGMBR retained most cells with granules, thereby reducing their penetration through membrane and thus the chance to form internal fouling layer. The internal biofilm layer was principally composed of live cells embedded in a matrix of proteins and polysaccharides, with that on AGMBR denser and thicker than that on MBR. Prevention of development of internal biofilm is essential to reduce irreversible fouling of AGMBR and MBR membranes.

Effect of two-stage coagulant addition on coagulation-ultrafiltration process for treatment of humic-rich water

A novel two-stage coagulant addition strategy applied in a coagulation-ultrafiltration (UF) process for treatment of humic-rich water at neutral pH was investigated in this study. When aluminum sulfate (alum) doses were set at a ratio of 3:1 added during rapid mix stage and half way through flocculation stage, the integrated process of two-stage alum addition achieved almost the same organic matter removal as that of conventional one-stage alum addition at the same overall dose. Whereas membrane fouling could be effectively mitigated by the two-stage addition exhibited by trans-membrane pressure (TMP) developments. The TMP developments were found to be primarily attributed to external fouling on membrane surface, which was closely associated with floc characteristics. The results of jar tests indicated that the average size of flocs formed in two-stage addition mode roughly reached one half larger than that in one-stage addition mode, which implied a beneficial effect on membrane fouling reduction. Moreover, the flocs with more irregular structure and lower effective density resulted from the two-stage alum addition, which caused higher porosity of cake layer formed by such flocs on membrane surface. Microscopic observations of membrane surface demonstrated that internal fouling in membrane pores could be also remarkably limited by two-stage alum addition. It is likely that the freshly formed hydroxide precipitates were distinct in surface characteristics from the aged precipitates due to formation of more active groups or adsorption of more labile aluminum species. Consequently, the flocs could further connect and aggregate to contribute to preferable properties for filtration performance of the coagulation-UF process. As a simple and efficient approach, two-stage coagulant addition strategy could have great practical significance in coagulation-membrane processes.