Total Fouling Research Articles

Biofouling in ultrafiltration process for drinking water treatment and its control by chlorinated-water and pure water backwashing

We investigated biofouling in ultrafiltration (UF) for drinking water treatment and its control by backwashing with chlorinated-water or pure water. By using sodium azide to suppress biological growth, the relative contribution of biofouling to total fouling was estimated, and its value (5.3–56.0%) varied with the feed water, and increased with the increases of filtration time and membrane flux. The biofouling layer could partially remove biodegradable organic matter and ammonia (32.9–74.2%). Backwashing using chlorinated-water partly inactivated the microorganisms (23.8%) but increased the content of extracellular polymeric substances (7.7%) in the biofouling layer. In contrast, backwashing using pure water led to a looser and more porous fouling layer according to optical coherence tomography observation. Consequently, the latter was more effective in reducing fouling resistance (33.41% reduction) compared to backwashing by chlorinated-water (8.6%). These findings reveal the critical roles of biofouling in pollutants removal in addition to membrane permeability, which has important implications for addressing seasonal ammonia pollution.

Diatomite precoat filtration for wastewater treatment: Filtration performance and pollution mechanisms

As wastewater processing facilities deal with increasing amount in combination with enhanced environmental pressures, diatomite precoat filtration is becoming one of the promising methods for wastewater treatment. Filtration performance of diatomite precoat filtration with five different coating layer thicknesses for wastewater treatment was investigated in terms of permeate flux, fouling grade, filtration resistance, permeate quality and fouling reversibility. Pollution mechanism was revealed by fitting Hermia’s fouling models, detecting the pollutant transport and analyzing the changes in microstructure of diatomite. The optimal thickness of diatomite precoat filtration was 4mm, which exhibited that the highest average permeate flux was 16.53L/m2h, total fouling resistance reduced by 59.5%, and lowest cake water content was 55.1%. Contact angle measurement indicated that the fouling formed on the diatomite coating layer was highly reversible. Compared with individual fouling model, the combination of three Hermia’s fouling models at different stages fitted the flux data well. FESEM images of diatomite particles confirmed high filtration flux and supported the pollutant transport results. The superiority of diatomite precoat filtration in improving filtration performance and mitigation fouling was demonstrated. The present study could also provide an experimental basis for optimizing precoat filtration process.

Redundancy analysis for determination of the main physicochemical characteristics of filtration membranes explaining their fouling by peptides

Peptide fouling is a technological drawback in filtration membrane processes. The impact of membrane characteristics on fouling by peptides from a complex whey protein hydrolysate (WPH) fouling was assessed based on advanced statistical redundancy analysis. Six membranes were characterized and tested: PES, PVDF, CF55, S11, S11+ and S11-. Among the eight physicochemical characteristics analyzed, zeta-potential (ZP) and roughness (Rz) were highly correlated with total fouling quantity (TFQ), suggesting that peptide fouling was mainly due to electrostatic interactions over wider surfaces. Concerning peptide sequences, redundancy analysis indicated that at least one characteristic among ZP, Rz, contact angle and thickness contributed significantly to the fouling of ALMPHIR, LIVTQTMK, TKIPAVFK, VLVLDTDYK, TPEVDDEALEK, TPEVDDEALEFDK or SLAMAASDISLLDAQSAPLR. It appeared that membranes with hydrophilic surfaces were more likely to be fouled by WPH regardless the peptide hydrophilicity. Besides, wider surface would enable more contact area for peptides, increasing consequently fouling. The TFQ was described by a statistical predictive model using the combined effect of ZP and Rz, of the form: ln(TFQ) = 8.64 + 0.072.XRz + 0.088.XZP (R2 = 0.9098). Moreover, statistical models were also established for each peptide, enabling to predict their specific fouling on a variety of membranes with different physicochemical characteristics.

Evaluation of fouling in nanofiltration for desalination using a resistance-in-series model and optical coherence tomography

Resistance-in-series models have been applied to investigate fouling behavior. However, it is difficult to model the influence of morphology on fouling behavior because resistance is indirectly calculated from the water flux and transmembrane pressure. In this study, optical coherence tomography (OCT) was applied to evaluate the resistance of the fouling layer based on fouling morphology. Sodium alginate, humic acid, and bovine serum albumin (BSA) with high salts concentrations (conductivity: 23 mS/cm) were used as model foulants. At the same total fouling resistance, BSA showed the highest cake layer thickness (BSA (114.5 μm) > humic acid (53.5 μm) > sodium alginate (20.0 μm)). However, a different order was found for the cake layer resistance (BSA > sodium alginate > humic acid). This indicates that fouling thickness is not correlated with cake layer resistance. According to the Carman–Kozeny equation, fouling layer porosity decreased in the following order: humic acid (0.30) > BSA (0.21) > sodium alginate (0.20). In addition, we provided a specific value that was calculated using the ratio between the fouling thickness and cake layer resistance. The results show that alginic acid induced a stronger cake layer resistance, despite its thin fouling layer, whereas BSA showed a relatively low potential for inducing cake layer resistance. The results obtained in this study could be used for estimating and predicting fouling behavior.

Novel insights into the role of Pseudomonas quinolone signal in the control of reverse osmosis membrane biofouling

The role of the Pseudomonas quinolone signal (PQS) pathway in the control of biofouling in reverse osmosis membrane filtration was examined by inoculating Pseudomonas aeruginosa into feed water to simulate biofouling. Various concentrations of PQS (2-heptyl-3-hydroxy-4-quinolone) and an anthranilate analog (methyl anthranilate) were used as the activator and inhibitor of the PQS pathway, respectively. Membrane performance results showed that addition of exogenous PQS caused severe decreases in permeate flux and salt rejection and increase in irreversible membrane fouling. In contrast, the presence of methyl anthranilate mitigated the declines in permeate flux and salt rejection by biofouling and significantly reduced the total fouling resistance and hence shorten the membrane cleaning periods. Biofilm characterization demonstrated that PQS aggravated membrane biofouling by promoting initial bacterial attachment, increasing levels of the extracellular polymeric substances (EPS), total organic carbon (TOC) and extracellular DNA, and changing the mature biofilm structure from a mushroom shape to a denser flat shape. In contrast, addition of methyl anthranilate increased protein adsorption during the initial biofouling stage through electrostatic interactions, but significantly inhibited biofilm growth via reducing levels of EPS and TOC, as well as total cell number in the biofilm. These results provide evidence that PQS pathway plays an important role in biofilm formation and an anthranilate analog, methyl anthranilate, could be a novel agent to control RO membrane biofouling. Therefore, PQS synthetic pathway and precursors of quorum sensing signals may provide viable targets for biofouling control in practical RO membranes applications.

Mitigation of HA, BSA and oil/water emulsion fouling of PVDF Ultrafiltration Membranes by SiO2-g-PEGMA nanoparticles

In this work antifouling poly(vinylidene fluoride) (PVDF) ultrafiltration membranes were synthesized with direct blending of Poly(ethylene glycol) methyl ether methacrylate (PEGMA)-grafted SiO2 (SiO2-g-PEGMA) nanoparticles (NPs) in the casting solution by phase inversion method. Chemical structure of the SiO2-g-PEGMA NPs was analyzed by Fourier transform infrared (FTIR) spectroscopy. Effect of different wt.% of SiO2-g-PEGMA NPs on the structure and performance of prepared membranes were examined by Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, Field emission scanning electron microscope (FESEM), Liquid–liquid displacement porosimetry (LLDP), pure water flux (PWF), hydraulic permeability, solute rejection study, water contact angle, water uptake, porosity and bovine serum albumin (BSA) adsorption. Modified membranes have higher solute rejection than plain PVDF membrane. Also, modified membrane with 0.5 wt% of SiO2-g-PEGMA NPs showed enhanced porosity, pore density, pore area, PWF and permeability. Water contact angle and amount of adsorbed BSA for the modified membrane with 1 wt.% of SiO2-g-PEGMA NPs were 50.7° and 0.05 mg/cm2 compared to 68.7° and 0.17 mg/cm2 respectively, for the plain membrane. Furthermore, antifouling property and rejection performance of modified PVDF membranes were investigated by humic acid (HA), BSA and oil-in-water (o/w) emulsion ultrafiltration experiment. It was observed from ultrafiltration study that the irreversible fouling and total fouling were decreased and achieved high flux recovery ratio for modified membrane.

Integrated aerobic granular sludge and membrane process for enabling municipal wastewater treatment and reuse water production

Aerobic granular sludge (AGS), as an aggregate of numerous self-immobilized functional microorganisms, has been recognized as an increasingly viable option for wastewater treatment and reuse water production. This study aimed at evaluating the application of AGS reactor as primary, ultrafiltration (UF) as secondary and nanofiltration (NF) as tertiary treatment for the treatment of municipal wastewater, focusing on determining the membrane fouling mechanism and reuse water production. AGS reactor, UF and NF exhibit high removal efficiency for COD (51.33%, 90.48% and 99.26%) and nutrients (53.63%, 94.84% and 98.06% total nitrogen, and 49.8%, 97.07% and 98.73% phosphorus), indicating that the integrated aerobic granular sludge and UF/NF process could provide high pollution removal and quality reuse water. As for filtration behavior of UF and NF, shear stress produced by agitation speed could significantly improve flux, due to the dispersion of pollutants. Besides, for AGS, improved simultaneous nitrification and denitrification by the internal anaerobic, anoxic, and aerobic structure and the richer biological community increased foulant removal, while the larger pore size and mature structure also reduced foulant deposition. Moreover, shear stress also diminished the total fouling resistance, reversible fouling and irreversible fouling, as well membrane cleaning efficiency was promoted, by controlling AGS deposition on membrane. In addition, the fouling mechanism of conventional floc sludge and that of AGS were deeply analyzed and respectively compared, from three aspects, namely, Scanning Electron Microscope (SEM), Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscope (AFM). Overall, the results demonstrated an alternative option for water treatment and reuse water production in an integrated AGS and membrane process.

Evaluating the effects of organic matter bioavailability on nanofiltration membrane using real-time monitoring

We studied the influence of bioavailability of organic matter on membrane fouling layer development by comparing the filtration performance of two feed waters (wetland water and graywater). Dissolved organic carbon (DOC) concentration, size exclusion chromatography (SEC), and fluorescence excitation-emission matrix (FEEM) were used to characterize the bioavailability of organic matter in these water samples during the nanofiltration process. The wetland sample contained a high proportion of humic acid- and fulvic acid-like matter with low bioavailability, whereas the graywater sample comprised substantial amounts of aromatic proteins and microbial byproduct-like matter with high bioavailability. In addition, the molecular size distribution revealed that the wetland sample contained a large portion of recalcitrant organic matter, whereas the graywater sample contained easily bioavailable organic matter. After the filtration experiment, the DOC of the wetland sample decreased to 4.8mgC/L, whereas the graywater sample resulted in a lower DOC concentration of 3.4mgC/L. Optical coherence tomography (OCT) illustrated real-time variations in the fouling layer morphology, providing both 2D and 3D images. In addition, confocal laser scanning microscopy (CLSM) quantified the bacterial volume in the fouling layer. The wetland sample yielded a bacterial volume of 11.8µm3/μm2 from a total fouling volume of 103µm3/μm2, whereas the graywater sample yielded a bacterial volume of 53.2µm3/μm2 from a total fouling layer volume of 134µm3/μm2. Fitting of the two-phase Monod model to the fouling layer growth on the membrane resulted in lower-yield coefficients (i.e., the volumes produced per unit amount of substrate, Yxs) of 7.46 and 27.95µm3/μm2 in wetland water and higher-yield coefficients of 13.17 and 47.53µm3/μm2 in the graywater at first and second phase, respectively. This study addresses the quantitative evaluation of the organic matter bioavailability in terms of membrane fouling using OCT images and a two-phase Monod model.

Performance and membrane fouling of a step-fed submerged membrane sequencing batch reactor treating swine biogas digestion slurry

ABSTRACTTo identify the performance of step-fed submerged membrane sequencing batch reactor (SMSBR) treating swine biogas digestion slurry and to explore the correlation between microbial metabolites and membrane fouling within this novel reactor, a lab-scale step-fed SMSBR was operated under nitrogen loading rate of 0.026, 0.052 and 0.062 g NH4+-N (gVSS·d)−1. Results show that the total removal efficiencies for NH4+-N, total nitrogen and chemical oxygen demand in the reactor (>94%, >89% and >97%, respectively) were high during the whole experiment. However, the cycle removal efficiency of NH4+-N decreased significantly when the nitrogen loading rate was increased to 0.062 g NH4+-N (gVSS·d)−1. The total removal efficiency of total phosphorus in the step-fed SMSBR was generally higher than 75%, though large fluctuations were observed during the experiments. In addition, the concentrations of microbial metabolites, i.e., soluble microbial products (SMP) and extracellular polymeric substances (EPS) from activated sludge increased as nitrogen loading rate increased, both showing quadratic equation correlations with viscosity of the mixed liquid in the step-fed SMSBR (both R2 > 0.90). EPS content was higher than SMP content, while protein (PN) was detected as the main component in both SMP and EPS. EPS PN was found to be well correlated with transmembrane pressure, membrane flux and the total membrane fouling resistance. Furthermore, the three-dimensional excitation-emission matrix fluorescence spectroscopy results suggested the tryptophan-like protein as one of the main contributors to the membrane fouling. Overall, this study showed that the step-fed SMSBR could be used to treat swine digestion slurry at nitrogen loading rate of 0.052 g NH4+-N (gVSS·d)−1, and the control strategy of membrane fouling should be developed based on reducing the tryptophan-like PN in EPS.

Bismuth Chelate‐Doped Microfiltration Membrane and Its Anti‐Biofouling Performance During a High‐Flux Membrane Bioreactor Operation

The main disadvantage of membrane bioreactor (MBR) technology, which is an important alternative for advanced wastewater treatment, is fouling. In this regard, polyether sulfone (PES) membranes were prepared by adding bismuth 2,3‐dimercapto‐1‐propanol (BisBAL) chelate to the dope solution for biofouling control. BisBAL was synthesized using bismuth metal and a thiol. The bare and BisBAL‐doped PES membranes were tested for their physical properties and biofouling resistance properties using xanthan gum solution as a model foulant and real activated sludge. The results showed that the BisBAL‐doped PES membrane has a lower absorptive surface and fouling tendency when compared to the bare PES membrane. Bismuth release from BisBAL‐doped PES membrane during pure water filtration was measured using inductive‐coupled plasma spectrometry and the results showed that bismuth release from BisBAL‐doped PES membrane was quite low. According to the MBR operation results, it can be said that the rate of transmembrane pressure increase, total fouling and biofilm creation could be decreased with BisBAL‐doped PES membrane usage without any effect on activated sludge structure and microbial community population in the MBR. BisBAL‐doped PES membranes did not lose their durability and anti‐biofouling activities in time and could be chemically washed. The novelty of this study was the application of a microfiltration membrane manufactured with bismuth metal in MBR operation.

Fluorescent natural organic matter responsible for ultrafiltration membrane fouling: Fate, contributions and fouling mechanisms

Membrane fouling has been a main obstacle to the success of ultrafiltration (UF) technology. Recently, fluorescent natural organic matter (FNOM), including humic-like substances (HS) and protein-like substances, has been recognized as substances responsible for membrane fouling. In this study, the matrix of FNOM in natural river water was substantially modified by combined coagulation and powdered activated carbon adsorption to enhance the diversity of the FNOM matrix. Fluorescence excitation emission matrix spectroscopy was employed to characterize FNOM components during the UF process. The correlations between FNOM components of the feedwater and membrane fouling were evaluated for the initial period and long-term operation. Reliable correlations of the maximum fluorescence intensity of HS with initial membrane fouling indicated that HS were major foulants in the initial period. Furthermore, the protein-like component exhibited significant correlation with the concentration effect fouling (R2 = 0.6131) and with irreversible fouling (R2 = 0.8711). We found that the fouling mechanism changed from pore obstruction to a protein concentration polarization layer followed by protein cake layer filtration. Total fouling of the UF membrane over long-term operation was alleviated with powdered activated carbon (PAC) adsorption; however, the mitigation of irreversible fouling was dependent on whether PAC adsorbed protein-like substances.

Investigation of antifouling performance a novel nanofibrous S-PVDF/PVDF and S-PVDF/PVDF/GO membranes against negatively charged oily foulants

Novel electrospun nanofibrous microfiltration membranes (ENMs) are fabricated by using sulfonated polyvinylidene fluoride (S-PVDF)/PVDF and S-PVDF/PVDF/graphene oxide (GO) with negative charge which was prepared by electrospinning technique. The GO with different weight percentages (0, 0.1, 0.5 and 1.0wt%) was used as additive in membrane and its effect on hydrophilicity, pure water flux, mean fiber and pore diameter was studied. The results showed that the most appropriate amount of GO is 0.5wt% (low contact angle (77.08°) with high pure water flux (1222L/m2h) was obtained). Therefore, in the fabrication of the rest of the membranes 0.5wt% GO was utilized as optimal amount of GO. In addition, the effects of sulfonation on morphology, oil removal, and fouling parameters were investigated. Finally, data analysis indicated that among the novel prepared ENMs, M8 (S-PVDF/PVDF/GO-50/50=volume ratio) displayed the lower irreversible fouling (41%), the highest flux recovery ratio (59%), and the superior antifouling properties. This higher antifouling performance of the M8 compared with other novel ENMs was attributed to hydrophilicity and enhanced strong electrostatic repulsion force between the membrane matrix and the oily foulant. The low degree of total fouling (70%) for the intact PVDF nanofibrous compared with novel ENMs (91–97%) was interpreted by the bigger pore diameter (300nm) of the intact PVDF nanofibrous.

Evaluation of biochar-ultrafiltration membrane processes for humic acid removal under various hydrodynamic, pH, ionic strength, and pressure conditions

The performance of an ultrafiltration (UF)-biochar process was evaluated in comparison with a UF membrane process for the removal of humic acid (HA). Bench-scale UF experiments were conducted to study the rejection and flux trends under various hydrodynamic, pH, ionic strength, and pressure conditions. The resistance-in-series model was used to evaluate the processes and it showed that unlike stirred conditions, where low fouling resistance was observed (28.7 × 1012 m−1 to 32.5 × 1012 m−1), higher values and comparable trends were obtained for UF-biochar and UF alone for unstirred conditions (28.7 × 1012 m−1 to 32.5 × 1012 m−1). Thus, the processes were further evaluated under unstirred conditions. Additionally, total fouling resistance was decreased in the presence of biochar by 6%, indicating that HA adsorption by biochar could diminish adsorption fouling on the UF membrane and thus improve the efficiency of the UF-biochar process. The rejection trends of UF-biochar and UF alone were similar in most cases, whereas UF-biochar showed a noticeable increase in flux of around 18–25% under various experimental conditions due to reduced membrane fouling. Three-cycle filtration tests further demonstrated that UF-biochar showed better membrane recovery and antifouling capability by showing more HA rejection (3–5%) than UF membrane alone with each subsequent cycle of filtration. As a result of these findings, the UF-biochar process may potentially prove be a viable treatment option for the removal of HA from water.

Effect of filtration mode and backwash water on hydraulically irreversible fouling of ultrafiltration membrane

To investigate the effect of filtration mode and backwash water on ultrafiltration (UF) membrane performance, total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) for constant pressure (CP) filtration and constant flux (CF) filtration were compared. Kaolin, humic acid (HA) and sodium alginate (SA) solutions were used as feed solutions, and then the fouled membranes were backwashed with UF permeate or ultrapure water. Results showed that when the kaolin solution was filtrated, the filtration mode had a limited effect on the membrane fouling, and low TFI and HIFI were observed. When HA and SA solutions were filtrated, the TFI of UF under CP mode was comparable to or slightly higher than that under CF mode. Higher TFI was observed at a hydrophobic membrane, a high filtration strength, a high feed concentration, a low pH, a high ionic strength, and a low Ca2+ concentration. When the UF permeate was used as the backwash water, the HIFI for the UF operated under CF mode was significantly less than that under CP mode. Low irreversible fouling was obtained when the ultrapure water was used for backwashing, and the HIFI for the UF under different filtration modes was almost identical.

Membrane Bioreactor (MBR) as Alternative to a Conventional Activated Sludge System Followed by Ultrafiltration (CAS-UF) for the Treatment of Fischer-Tropsch Reaction Water from Gas-to-Liquids Industries

The potential of a membrane bioreactor (MBR) system to treat Fischer-Tropsch (FT) reaction water from gas-to-liquids (GTL) industries was investigated and compared with the current treatment system: a conventional activated sludge system followed by an ultrafiltration (CAS-UF) unit. The MBR and the CAS-UF systems were inoculated with municipal activated sludge and operated in parallel for 645 days with four interruptions using synthetic FT reaction water. Both treatment systems achieved a removal efficiency of 98 ± 0.1% within 60 days after inoculation, the COD influent concentration was 1014 ± 15 mg L−1. This suggests that MBRs form a suitable alternative to CAS-UF systems for the treatment of FT reaction water from the GTL industries. Moreover, the total fouling rates (Ft) of the membranes used from day 349 till the end were assessed. The average Ft was 7.3 ± 1.0 1010 m−1 day−1 for CAS-UF membranes and 2.8 ± 00.7 1010 m−1 day−1 for MBR-MT membranes. This indicates that MBR systems for the treatment of FT reaction water from the gas-to-liquids industries are less prone to fouling than CAS-UF systems.

Monitoring UF membrane performance treating surface-groundwater blends: Limitations of FEEM-PARAFAC on the assessment of the organic matter role

The decrease of water quantity and quality in water scarcity areas is palliated by improving water treatments with membrane technologies. System performance and efficiency, and then cost, is mainly affected by membrane fouling, which is still not well understood and controlled appropriately. In this study, the influence of content and composition of dissolved organic matter (DOM) on a membrane ultrafiltration (UF) stage from a full-scale UF stage in a drinking water treatment plant (DWTP) fed with surface water, groundwater (or blends of them) was investigated. Excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) was used to characterize and assess DOM changes in water samples Water streams feeding the UF stage showed high variability in DOM content and composition. FEEM-PARAFAC analysis allowed the differentiation of seven different organic components. Additionally to the characterization and monitoring of DOM in the full-scale UF stage, a bench scale UF pilot was run to experimentally correlate the impact of water quality with membrane performance. The experiments included testing synthetic solutions of model foulants (synthetic humic acid and bovine serum albumin) and blends of complex waters. To quantify fouling, the total fouling index (TFI) and the hydraulically irreversible fouling index (HIFI) were calculated for each filtration run. According to the results obtained, the correlation plots between the PARAFAC components and the fouling indices pointed at microbial byproducts (C1) and humic-like components (C2, C4, C5) as the ones showing higher correlations.

Optimization of air scouring for an effective control of membrane fouling in submerged MBR

A membrane module including grid was designed and introduced to MBR (membrane bio-reactor) for the purpose of better control of membrane fouling. It could be anticipated that the grid enhances the shear force of fluid-air mixture into the membrane surface by even-distributing the fluid-air to the membrane module. As MLSS concentration, packing density which is expressed in the ratio of the housing and the cross-sectional area of membrane fibers (Am/At) and air-flow rate were changed, membrane foulings were checked by monitoring fouling resistances. The total fouling resistance (Rc+Rf) without grid installation (i.e., control) was 2.13×1012 m-1 , whereas it was reduced to 1.69×1012 m-1 after the grid was installed. Regardless of the grid installation, the Rc+Rf increased as the packing density increased from 0.09 to 0.28, however, the increment of resistance for the grid installation was less than that of the control. Increase in the air flow rate did not always guarantee the reduction of fouling resistance, indicating that the higher air flow rate can partially de-flocculate the activated sludge flocs, which led to severer membrane fouling. Consequently, installation of grids inside the housing have brought a beneficial effect on membrane fouling and optimum air flow rate is important to keep the membrane lowering fouling.

A New Approach to Modeling Operational Conditions for Mitigating Fouling in Membrane Bioreactor.

Modeling and optimization tools play a key role in membrane fouling control in membrane bioreactor (MBR) systems by delineating the more important variables involved. In this study, the influence of sludge retention time (SRT), aeration rate and filtration mode on hollow fiber membrane fouling was investigated. Using the response surface methodology (RSM) for modeling and central composite rotatable design (CCRD) for design of experiments, mathematical models were developed for fouling rate and protein (P1, P2) and carbohydrate (C1, C2) concentrations in two layers of fouling. Results showed that sludge retention time (SRT) was the most important variable in most models followed by aeration rate. Aeration showed a more effective role on the models of the rinsed layer (P1, C1) than backwashed layer (P2, C2). Backwashed layer had more influence on total fouling rate than rinsed layer. The optimal point for MBR operation was: SRT = 30 days, aeration = 10.7 L/min, relaxation interval = 8.8 minutes, and relaxation duration = 41.8 seconds.

Feasibility of sweeping gas membrane distillation on concentrating triethylene glycol from waste streams

High treatment efficiency and low energy consumption are desired factors for any process intensification from an industrial prospective. It can be noted to be the same for membrane-based processes for treating triethylene glycol (TEG) wastewater, which is generated from dehydration step in natural gas processing. In this study, sweeping gas membrane distillation (SGMD) was applied to investigate both the potential of process intensification of triethylene glycol (TEG) from binary solutions (water and TEG) and from real wastewater. A hydrophobic hollow fiber membrane module (0.255m2) was operated with both synthetic and real TEG wastewater. The feasibility of SGMD for concentrating TEG was done by evaluating various key factors which where; optimizing operating condition like feed temperature, feed flow rate, and sweeping gas flow rate vs permeate flux, energy consumption evaluation and fouling analysis. Experimental results showed that SGMD had the ability to concentrate TEG in real wastewater till 98%. During concentrating TEG from 9.69 to 50%, the permeate flux was in the range from 1.6 to 2.4kg/m2h with the ratio of energy of 1.4kWh/kg. In regard to fouling, estimations were made for total resistance, membrane resistance, boundary layer resistance and fouling resistance. Fouling contributed 69.2, 7.6, and 23.2% respectively, whereas irreversible resistance accounted for 2% of the total fouling. The results, indicate that bench scale SGMD was able to concentrate TEG up to 98% and potential for pilot scale studies are in need for further scale up.

Fouling behaviors correlating to water characteristics during the ultrafiltration of micro-polluted water with and without the addition of powdered activated carbon

The aim of this paper was to investigate the effects of powdered activated carbon (PAC) pretreatment on the fouling behavior of an ultrafiltration (UF) membrane during micro-polluted water treatment. The results of this study demonstrated that PAC had a positive influence on fouling mitigation. Specifically, PAC-pretreated water had lower fouling resistances (FRs) and fouling indexes (FIs) than raw water. Liquid chromatography combined with peak-fitting analyses of raw water with and without PAC pretreatment suggested that PAC adsorption was much effective in reducing the contents of the low molecular weight acids and building blocks (LMWA&BB) and the humic substance (HS) fractions in raw water. Principal component analysis (PCA) was also used to identify the fouling behaviors associated with the characteristics of the water samples. Significant correlations (r2) of LMWA&BB with hydraulic reversible resistance (Rre), hydraulic irreversible resistance (Rir), total fouling index (TFI) and the hydraulically irreversible index (HIFI) were found (0.7534, 0.8430, 0.6297 and 0.7015, respectively), indicating that LMWA&BB contributed more significantly than biopolymers(BP) and HS to membrane fouling. The likely mechanism by which the PAC alleviated fouling was the reduction of the LMWA&BB fraction’s presence at the membrane surface and pores. These results suggest that the application of the PAC pretreatment preceding passage through the UF membrane is a promising approach for membrane fouling mitigation.