Affecting Membrane Fouling Research Articles

Gaining deeper insights into the bioflocculation process occurring in a high loaded membrane bioreactor used for the treatment of synthetic greywater

In the present study, a high loaded membrane bioreactor (HL-MBR) operated at a hydraulic retention time (HRT) of 1.5 h, and three different sludge retention times (SRTs) in the range of 0.5–2 days, was used for the treatment of synthetic greywater. The chemical oxygen demand (COD) removal efficiency of the system was in the range 87–89% at all SRTs. Bioflocculation efficiency (defined as the percentage of suspended COD in the concentrate stream), COD bio-oxidation, total extracellular polymeric substances (EPS), tightly bound (TB) EPS and the ratio of EPS protein (EPSp) to carbohydrate (EPSc) increased when SRT was increased from 0.5 to 2 days. Sludge supernatant soluble microbial products (SMP) increased with increase in SRT from 0.5 to 2 days, while the effluent SMP was negligible. Particle size distribution analyses revealed a bimodal distribution at an SRT of 0.5 days, and normal distributions at other SRTs. Furthermore, depending on the value of the F/M ratio, different SRTs in the range of 0.5–2 days had either positive or negative effects on the mean particle size. Linear correlation analyses were performed using the data obtained during both transient and steady-state operations of the HL-MBR system. TB-EPS and EPSp showed strong correlations with the biofloccultaion efficiency, whereas loosely bound (LB) EPS correlated with soluble COD removal. TB-EPS and EPSc had negative correlations with the energy recovery potential of the system. The trend of change of parameters affecting membrane fouling intensity with SRT suggested that, in the range studied, the lowest rate of membrane fouling would be expected at SRT of 0.5 days.

Characteristics of MBR Oily Sludge and Its Influence on Membrane Fouling under Two Aeration Modes

A membrane bioreactor (MBR) with ordinary aeration (reactor R1) and a MBR with microporous aeration (reactor R2) are conducted in parallel to investigate the characteristics of oily sludge and its effect on membrane fouling. The results indicate that the order of membrane fouling rate from high to low is: reactor R1 dissolved oxygen (DO) (1 mg/L) > reactor R2 DO (1 mg/L) > reactor R1 DO (4 mg/L) > reactor R2 DO (4 mg/L). Membrane fouling rate is not related to oily sludge concentration but to oily sludge sedimentation performance and the small particle oily sludge is the key factor to affect the membrane fouling. The soluble microbial products (SMP) are examined by three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra. 3DEEM spectra demonstrate that the main organic substances of the SMP in two reactors are tyrosine aromatic protein, fulvic acid-like substances and soluble microbial products under DO are1 mg/L and 4 mg/L, respectively. The proportion sum of fulvic acid-like substances and soluble microbial products is the key factor affecting membrane fouling, and membrane fouling accelerates as the ratio increases.

Membrane Fouling Prevention and Control Strategies in Pulp and Paper Industry Applications: A Review

Membrane separation technologies have recently received much attention, from lab-scale studies to full-scale operations, in the forest industry. However, membrane fouling comprises a signifcant obstacle to their broad application. Thus, to ensure cost-effective operation of membrane separation processes, the improved elucidation of membrane fouling and establishment of effective fouling control strategies are critical. Membrane fouling decreases process performance efciency, thereby increasing operational and maintenance costs. Although much research has been conducted in this feld, a review has not yet been undertaken to address membrane fouling in pulp and paper mill applications. Further, membrane fouling is still not fully understood. In this review, a survey of the present state of fouling management strategies in the pulp and paper industry (PPI) is presented alongside the latest advances and innovative methods in fouling management. This article also discusses the key parameters that affect membrane fouling, fouling characterization techniques, as well as fouling mechanisms and strategies that are employed for fouling control. In addition, future research opportunities related to membrane fouling control strategies in both low-pressure membranes and MBRs are proposed.

Microbial fuel cell technology as a downstream process of a membrane bioreactor for sludge reduction

Recently, microbial fuel cells (MFCs) have been integrated with membrane bioreactors (MBRs), either in an internal or an external configuration, for wastewater treatment and energy recovery. In an external configuration, MFCs could be applied for an efficient sludge reduction since they can simultaneously address energy issue and environmental concerns associated with sludge treatment.In the present study, a potentiostatic controlled microbial fuel cell (MFC) was fed with activated sludge from a membrane bioreactor (MBR) at different total suspended solid (TSS) concentrations (1–10gTSSL−1) in order to assess the electrochemical response of the system and the impact of the bioelectrochemical treatment on sludge characteristics and membrane fouling parameters. The MFC showed COD removals 30% higher than the control test and a reduction of volatile suspended solids (VSS) up to 43% with concomitant production of energy (maximum current density of 2.0Am−2). The electricity production increased with the increase of TSS content. In both MFC and the control test, an increase of soluble microbial products (SMP) ratio in terms of proteins and carbohydrates (SMPp/SMPc) and an average 50% increase of sludge hydrophobicity were observed. This could limit membrane fouling in the case that the sludge is recirculated to the MBR. The electrochemical characterization indicated that both, acetate and sludge oxidation took place at a similar formal potential of −0.2V vs. SHE indicating that both used the same electron transfer mechanism. Hence, this study shows that a MFC could oxidize, reduce and stabilise MBR sludge producing electricity and affecting membrane fouling parameters.

Preparation, characterization and application of low-cost pyrophyllite-alumina composite ceramic membranes for treating low-strength domestic wastewater

To advance cost-effective strategies for developing flat-sheet ceramic microfiltration membranes, the feasibility of using waste mineral-based materials as a ceramic membrane in engineered membrane bioreactor systems (MBRs) for treating low-strength domestic wastewater was evaluated. The ceramic membrane support layers that had effectively been fabricated with pyrophyllite and alumina were sintered at 1350°C, and subsequently coated with alumina powder suspension to achieve a narrow pore size distribution. Membrane surface properties were characterized to understand the membrane fouling phenomenon in ceramic MBRs (CMBRs). Consistently high organic removal efficiency could be achieved under all investigated hydraulic retention times (HRTs) in the CMBRs. The physico-chemical sludge properties were measured to evaluate design parameters affecting membrane fouling for the CMBR. We further evaluated the performance of pyrophyllite-alumina composite ceramic membranes in a pilot-scale CMBR plant, with 1m3/d capacity that was constructed at an actual water resource recovery facility (WRRF), to improve nitrogen removal and produce high quality effluent through a combined process of modified Ludzack-Ettinger (MLE) and CMBR (MLE/CMBR). The MLE/CMBR was operated successfully up to 20 LMH, with the final effluent chemical oxygen demand (COD) being maintained below 16.3mg/L.

The characteristic of passive adsorption using the submerged hydrophilic membrane in biological treatment process

AbstractThis study investigated the calibration curves for the analysis of the protein and carbohydrate as foulants and the specific profiles of resistance and extracellular polymeric substances (EPS) through passive adsorption (at flux = 0) of hydrophilic polyethylene membrane in an activated sludge bioreactor. It is to recognize fouling and cleaning mechanisms of hydrophilic polyethylene material. Passive adsorption and cake formation continuously proceeded for six weeks even though flux was zero. sEPS more affected membrane fouling than eEPS because sEPS remained constant in the reactor when permeability resistance of membrane increased whereas eEPS continuously decreased. The result showed that 0.05% NaOCl was appropriate for accurately measuring the protein and carbohydrate. Resistance (Rf) of contaminated membrane was high as membrane submergence was proceeded by 43th day, then critical fouling presented. Recovery rate by physical and chemical cleaning decreased as membrane permeation kept doing and...

Hybrid water treatment process of carbon fiber microfiltration and photocatalyst-coated polypropylene beads: roles of humic acid, photo-oxidation, and adsorption

AbstractThe effect of organic matters on membrane fouling was observed in a hybrid process of tubular carbon fiber microfiltration (MF) and polypropylene (PP) beads coated with TiO2 photocatalyst with periodic water back-flushing for advanced water treatment. Also, the treatment portions of membrane filtration, photocatalyst adsorption, and photo-oxidation were investigated by comparing the treatment efficiencies of (MF), (MF + TiO2), and (MF + TiO2 + UV) processes. The periodic water back-flushing was performed during 10 s per 10 min filtration to reduce membrane fouling. As results, the organic matter, such as humic acid (HA), could be one of the main factors affecting membrane fouling, because the resistance of membrane fouling (Rf) increased significantly as increasing HA concentration. The treatment efficiencies of turbidity increased a little; however, those of dissolved organic matters (DOM) increased dramatically as increasing HA. As a result of investigating the roles of membrane filtration, adso...

Integrated in-line coagulation-aerated ultrafiltration for drinking-water production: A case study from laboratory to pilot plant

A pilot-scale study was made for drinking-water production from low-quality influents with in-line coagulation as pre-treatment of aerated ultrafiltration. Optimum flocculation parameters were previously determined in the laboratory, searching for large and strong flocs that could resist aeration without increasing the membrane fouling. Nevertheless, the comparison of the jar tests and the pilot-scale results showed that the former could help pre-dimensioning the flocculation facilities but could not precisely reproduce the behavior of the flocs in the membrane tank. The optimum coagulant dosage enabled the highest dissolved organic carbon (DOC) removal without affecting membrane fouling. Additionally, as opposed to the jar-test results, long retention times led to the lowest fouling rates while the velocity gradient affected neither the effluent quality nor the membrane fouling. These findings suggested that the influence of the flocculation parameters was masked by aeration inside the membrane tank but, even so, 43% and 82% DOC and UVA254 removals, respectively, were reached. Furthermore, the growth of the total membrane resistance with time was logarithmic instead of linear, confirming the suitability of the pre-treatment for low-quality influents.

Study on the Membrane Fouling of the Process of Using Two Layer Flat-Sheet Membrane for Sludge Thickening and Water Reuse

In this paper, the critical flux was applied to represent the tendency of membrane fouling. The response surface model was used to study different factors, such as sludge concentration, space between membranes and aeration rate, affecting membrane fouling of the upper and lower layer membrane module. It was found that the model is fitting and significant, moreover, the sludge concentration, space between membranes and aeration rate has a significant impact on the upper and lower membrane fouling. Meanwhile, it was also observed that the critical flux of both upper and lower layer membrane module sharply decreased with the increase of sludge concentration. However, the different variation tendency of membrane fouling between upper and lower layer membrane module was detected due to the change of space between membranes and aeration rate, when it was under different sludge concentrations. Finally, optimum operating parameters under different sludge concentration simulated by response surface model were successfully applied to the process of using flat-sheet membrane for four-stage sludge thickening.

Effect of humic acid, photo-oxidation, and adsorption at air back-flushing in hybrid water treatment of multi-channel alumina MF and photocatalyst-coated PP beads

The effect of humic acid (HA) on membrane fouling and treatment efficiency was observed in a hybrid process of seven channel alumina microfiltration (MF) and TiO2 photocatalyst-coated polypropylene (PP) beads with air back-flushing for advanced water treatment, and compared with the previous study with water back-flushing. As a result, the organic matter could be one of the main factors affecting membrane fouling because the final membrane fouling resistance decreased significantly as reducing HA concentration. The turbidity treatment efficiencies were very high as 95.5–98.3% independent of HA, but that of dissolved organic matters (DOM) was the maximal 80.1% at HA 8 mg/L. However, in the result with water back-flushing, the DOM treatment efficiency was almost constant between 78.9 and 81.8% independent of HA. Treatment portions of MF, photocatalyst adsorption, and photo-oxidation were investigated by comparing the treatment efficiencies of (MF), (MF + TiO2), and (MF + TiO2 + UV) processes. The membrane fouling resistance was the minimum at (MF + TiO2 + UV) process. It means that the photo-oxidation and adsorption could control membrane fouling in the hybrid water treatment process. The role of adsorption was more important than that of photo-oxidation in the hybrid process with air back-flushing; but, the role of photo-oxidation was a little more important than that of adsorption in the result with water back-flushing for DOM treatment.

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.

Aluminum-humic colloid formation during pre-coagulation for membrane water treatment: Mechanisms and impacts

Precoagulation has been widely used by low pressure membrane filtration (LPMF) plants to reduce membrane fouling and increase natural organic matter (NOM) removal. Formation of aluminum and aluminum-NOM moieties plays a fundamental role in this important water treatment process. This study comprehensively investigated the mechanisms of aluminum-NOM species formation during precoagulation and their impacts on LPMF performance. The results show that, at low alum doses, e.g. 0.5 mg and 1.0 mg Al L−1, humic substances (HS) and Al species (amorphous Al(OH)3, or Al(OH)3(am)) reacted to form small Al(OH)3(am)-HS colloids. Increases in alum dose resulted in sequential transitions of the Al-HS moieties to larger particles and, eventually, precipitates. Compared to waters containing only naturally occurring organic colloids (OC) or HS, the coexistence of OC and HS facilitated the formation of Al-HS precipitates, thereby increasing the removal of HS by 7–15%, but the removal of OC was decreased by 3–20%. Interestingly, these transitions in Al-HS moieties did not affect membrane fouling. Both short-term and long-term filtration results demonstrate that OC, rather than the Al(OH)3(am)-HS colloids, primarily caused membrane fouling. These findings highlight the dynamics of particulate Al-NOM formation during precoagulation and its relationship with membrane fouling, which can be utilized to optimize the operation of integrated precoagulation-LPMF systems on full-scale installations.

Role of photo-oxidation and adsorption at water back-flushing in hybrid water treatment of multi-channels alumina MF and PP beads coated with photocatalyst

The effect of organic matters on membrane fouling was observed in a hybrid process of seven-channel alumina microfiltration (MF) and polypropylene (PP) beads coated with TiO2 photocatalyst for advanced water treatment. As a result, the organic matter, like humic acid, could be one of the main factors affecting membrane fouling because the final resistance of membrane fouling decreased significantly due to reduction in humic acid concentration. The treatment efficiencies of turbidity were as high as 96.6–96.9% independent of humic acid concentration, but that of dissolved organic matters was the maximum, 65.4% at humic acid 6 mg/L. Treatment portions of membrane filtration, photocatalyst adsorption, and photo-oxidation were investigated by comparing the treatment efficiencies of (MF), (MF + TiO2), and (MF + TiO2 + UV) processes. The membrane fouling resistance was the minimum, and the final permeate flux and the total permeate volume were the maximum at (MF + TiO2 + UV) process. It means that the photo-oxidation could control membrane fouling, but the photocatalyst adsorption did not participate to reduce membrane fouling in our hybrid water treatment process. The photo-oxidation and the adsorption by PP beads coated with photocatalyst could play a much greater role to remove organic matter than turbid materials.

Bio-film and bio-entrapped hybrid membrane bioreactors in wastewater treatment: Comparison of membrane fouling and removal efficiency

Hybrid membrane bioreactors have emerged to alleviate membrane fouling, the drawback of conventional membrane. In this study immobilized acclimatized activated sludge on either polypropylene or polyurethane carriers were exploited to run two types of hybrid bioreactors and compare their performances with one conventional MBR in treatment of a synthesized phenolic wastewater at 1000mg/L and a hydraulic retention time of 13h. Immobilization on polyurethane foam resulted in phenol removal of 99% as compared to 72.5% for polypropylene and 70.6% for the conventional MBR. Complete membrane fouling occurring at trans-membrane pressure of 0.6bar was observed after 5, 9 and 21days for conventional MBR, polypropylene and polyurethane hybrid bioreactors, respectively. Additionally, analyses of soluble microbial products showed that proteins positively affect membrane fouling. The performance of hybrid bioreactor containing polyurethane foams under phenol loading shocks was also examined by sudden variations from 1000 to 1250 and 1500mg/L in influent phenol concentration where it was found that although persistent shocks had adverse effect on phenol removal, complete retrieval of phenol removal could be achieved after elimination of shocks. Among bioreactors examined, a hybrid bioreactor using polyurethane foam is therefore proposed as a superior bioreactor considering both performance efficiency and membrane fouling for wastewater treatment.

Effect of microwave irradiation on typical inorganic salts crystallization in membrane distillation process

This study is a continuation of our previous work on microwave-assisted membrane distillation. The crystal morphology of sodium chloride and calcium carbonate in the process of membrane distillation and microwave membrane distillation was investigated in this work. The effect of salt concentration on the ability of absorbing microwave of solution and the mass transfer of microwave membrane distillation were also analyzed. The results show that the ionic conduction is the main between two factors (ionic conduction and dipole rotation) which have effect on absorbing microwave. When the mass concentration of sodium chloride solution is up to 5%, the microwave energy absorbed by solution is almost five times as much as pure water. Moreover, the increase in salt concentration has no significant extra influence on the mass transfer of microwave membrane distillation. The crystallization experiments confirm that microwave irradiation do not affect membrane fouling or worsen it. The different effect of microwave irradiation on crystallization of two typical inorganic salts is observed in this study. For sodium chloride, the microwave heating leads to the decline of the total particle number, while the total deposition keeps constant and the size distribution of crystal particles becomes more uniform, compared with conventional heating. As for calcium carbonate, microwave irradiation not only increases the total deposition and total particle number, but also induces the crystals growth. Especially, it is found that microwave irradiation induces the crystals to grow toward aragonite. The ratios of the aragonite number to the total particle number increase from 28.0% and 56.5% to 81.1% and 85.8% at the two higher feed mass concentrations, respectively.

Interaction mechanisms associated with organic colloid fouling of ultrafiltration membrane in a drinking water treatment system

The Extended Derjaguin Landau Verwey Overbeek (XDLVO) approach was introduced to predict organic colloid fouling of membranes in an initial ultrafiltration (UF) phase. Two polymeric UF membranes, made of polyvinylchloride (PVC) and polyvinylidene fluoride (PVDF) respectively, were selected to investigate membrane fouling by filtering water samples with different organic colloid compositions. The experiment was performed to determine the fouling contributions of van der Waals (LW) interactions, electrostatic (EL) interactions, as well as double layer and short-range acid–base (AB) interactions, to the total interaction energy caused by organic colloids attaching to UF membrane surfaces. The results showed that LW interaction energy predominated when the distance between the membrane surface and organic colloid was >5nm, while AB accounted for a key contribution to total interaction energy over short distances (<2.5nm). The influence of EL interaction energy was ignored in the total interaction energy composition. The surface energy, among all characteristics of membrane material, was a dominant factor affecting membrane fouling. The experimental results of initial ultrafiltration of raw water from the actual water source were in accordance with the predictions based on XDLVO theory, indicating that it was a feasible option for predicting membrane fouling during the initial ultrafiltration phase.

Effects of heavy metal wastewater on the anoxic/aerobic-membrane bioreactor bioprocess and membrane fouling

Heavy metals have significant negative effects on anoxic/aerobic-membrane bioreactors (A/O-MBR). The changes in the performance of A/O-MBR fed with municipal wastewater containing 0.25-2.56 mg/L (low concentrations) and 3.7-32.3mg/L (high concentrations) of zinc, copper, lead, and cadmium were studied in this paper. The nitrification rate decreased to 27% and 46%, whereas the denitrification rate decreased to 20% and 34% under treatment with low/high concentrations of heavy metals, which indicate that heavy metals more significantly affect nitrification than denitrification. Heavy metals also resulted in the increase of carbohydrate of extracellular polymer substances and a smaller particle size distribution. Scanning electron microscope images, energy-dispersive X-ray spectroscopy and atomic absorption spectrometry analysis of fouled membranes showed solid inorganic scale deposits on the membrane. All these results suggest that heavy metals affect membrane fouling in two ways: (a) modification of sludge characteristics; and (b) contribution to inorganic fouling.

Fouling mitigation in membrane bioreactors using multivalent cations

Several cations have been used to study the effect of mineral coagulants on activated sludge properties and membrane fouling in submerged membrane bioreactors (MBRs). The flocculability and settling properties of activated sludge were studied in various concentrations of sodium, potassium, magnesium, calcium, ferrum (in Fe3+ form), and aluminum. Significant effect of cations and their concentrations on different parameters have been analyzed by 2-way ANOVA. Results showed that multivalent cations induce flocculation in bioreactors while monovalent cations have a detrimental effect on flocculability of activated sludge. The ratio of tight bound extracellular polymeric substances (TB-EPSs) to loosely bound (LB-EPSs) increased with concentration of multivalent cations that was in accordance with enhancement of biosorption in high concentration of multivalent cations. Moreover, these cations improved the settleability and dewatering properties of activated sludge. They also mitigated membrane fouling in the MBRs so that calcium and aluminum reduced membrane fouling to nearly 30%. Simple but useful correlations were developed for description of activated sludge properties based on easy measurable parameters that could be used also for estimation of membrane fouling. It was found that the ratio of TB-EPS to LB-EPS and also flocs size distribution are the main parameters affecting membrane fouling.

Performance of the sludge thickening and reduction at various factors in a pilot-scale MBR

In this study, the performance of a sludge thickening and reduction system coupled with filtration using a flat-sheet membrane was investigated. The effects of various factors such as HRT, flux and addition of coagulant were determined. TMP was observed to increase as the HRT decreases and the operating flux increases. The operating condition was then determined and the selected HRT and flux were 6.7days and 10.7L/m2h, respectively. Different operating HRT indicated the variation of hydraulic loading rates for the organics and other nutrients affecting membrane fouling, while varying the flux showed the rate of decrease of the membrane permeability. When coagulant was added, the rate of increase of TMP was decreased, allowing the system to be operated for a longer period of time. It was observed that inorganic coagulant was more effective than organic coagulant based on the final TMP. It also suggests that membrane fouling was better minimized with the addition of inorganic coagulant. It was found that the most essential factor on membrane fouling was the addition of coagulant, while the effect of HRT was observed to be the least influential among the other factors considered.

Graft polymerization and plasma treatment of polymer membranes for fouling reduction: A review

This article presents a review of recent developments in surface modification of polymer membranes via graft polymerization and plasma treatment for reduction of fouling with organic compounds and microorganisms in pressure driven membrane processes. The factors affecting membrane fouling, such as membrane hydrophilicity, charge and surface roughness are discussed. The recent studies in which the reduction of organic fouling and biofouling by the modification of the membrane surface via ultraviolet/redox initiated surface grafting of hydrophilic polymers and low temperature plasma treatment are reviewed.