Major Membrane Foulants Research Articles

Electrical responsiveness of carboxylate multi-walled carbon nanotube cross-linked composite anti-fouling membranes to organic pollutants

Protein has been identified as one of the major membrane foulants in wastewater treatment and reclamation applications. The specific molecular configuration of bovine serum albumin (BSA) impedes electron transfer at the interface, resulting in poor electrochemical signal, and is often used as a blocker for electrochemical biosensors. To improve the precision and speed of fouling detection, the study proposes integrating the electrical properties with the organic fouling process of the membrane to provide the BSA fouling electrical response signal. The unique electrical properties of carboxylate multi-walled carbon nanotubes (O-MWCNTs) were introduced into polyvinylidene fluoride (PVDF) ultrafiltration membranes using a pre-coating method. The conductive coated layer of O-MWCNT facilitates real-time observation of membrane fouling and enables timely cleaning of the membrane to improve fouling resistance. To improve the loading and binding strength of the O-MWCNTs, phenylenediamine (MXAD) was utilized as a cross-linking agent, which improved the composite membrane's overall performance and decreased the membrane's resistance from 1.33 × 106 Ω–37.91 Ω. The electrical signal received from the four-probe resistivity meter showed a response to the fouling level. The combined comparison of the normalized flux and electrical signal trends resulted in a more visual, rapid, sensitive, and accurate indication of membrane BSA fouling, which paves the way for the detection of electrical BSA fouling and subsequent cleaning and reuse of the separation membranes.

Comparison between permanganate pre-oxidation and persulfate/iron(II) enhanced coagulation as pretreatment for ceramic membrane ultrafiltration of surface water contaminated with manganese and algae

Concurrent presence of algae and manganese (Mn) in water poses a significant challenge for water treatment. This study compared the treatment efficiency of Mn-containing and algae-laden water using either permanganate pre-oxidation (KMnO4) or persulfate/iron(II) (PMS/Fe2+) enhanced coagulation as pretreatment for ceramic membrane ultrafiltration. The results showed that KMnO4 pre-oxidation achieved a slightly more effective Mn removal, and was almost unaffected by the initial dissolved organic carbon (DOC) concentrations. PMS/Fe2+ removed UV254 more efficiently (above 90% at a dose of 0.25 mmol/L), compared with KMnO4 (less than 60% UV254 removal). According to X-ray photoelectron spectroscopy (XPS) analysis of aggregates, both KMnO4 and Fe2+/PMS oxidation resulted in the formation of MnO2 precipitate. Electron paramagnetic resonance(EPR) analysis demonstrated that only the reactors dosed with PMS/Fe2+ were able to generate the highly reactive hydroxyl radical(·OH). The production of ·OH caused significant rupture of algal cells and thus higher algal removal compared to the treatment with KMnO4 (whereby insignificant cell breakage was observed). The cell rupture resulted in higher amounts of organic matter released in the systems containing PMS/Fe2+, as demonstrated by excitation-emission matrix (EEM) and protein analysis. Despite the elevated level of organic matter, adding PMS/Fe2+ was found to notably mitigate membrane fouling due to the formation of large flocs (311–533 μm) as well as the elimination of major ceramic membrane foulants, i.e. humic substances.

Effects of Solids Retention Time on the Anaerobic Membrane Bioreactor with Yttria-Based Ceramic Membrane Treating Domestic Wastewater at Ambient Temperature.

The effects of solid retention times (SRTs) (100 days, 50 days, 25 days) on the performance, microbial community, and membrane fouling of a lab-scale anaerobic yttria-based ceramic membrane bioreactor (AnCMBR) treating synthetic domestic wastewater at ambient temperature (31.2 ± 2.7 °C) were examined. The soluble chemical oxygen demand (SCOD) removal was higher (89.6%) at 25 days SRT compared with 50 days (39.61%) and 100 days (34.3%) SRT. At 100 days SRT, more Bacteroidetes, Firmicutes, and Proteobacteria were present in the microbial community. At 25 days SRT, more Chloroflexi, Synergistetes, and Pastescibacteria emerged, contributing to the stable performance. The SRT of 25 days has resulted in a more stable microbial community compared with 50 days and 100 days SRT. Both bacterial and archaeal community diversities were higher at 25 days SRT, and the specific production of soluble microbial by-products (SMPs) and extracellular polymeric substances (EPSs) were higher at 25 days SRT as well. Consequently, the membrane flux was lower at 25 days SRT with the increased particle size and the enhanced SMPs and EPSs production. Fourier transform infrared spectroscopy analysis (FTIR) and three-dimensional excitation and emission matrix (3D-EEM) analysis showed that protein and SMPs were the major membrane foulants at all SRT stages. In this study, SRT at 25 days was favorable for the stable operation of an AnCMBR treating domestic wastewater at ambient temperature.

Complexation between dissolved silica and alginate molecules: Implications for reverse osmosis membrane fouling

Dissolved silica and organic matter are major membrane foulants in desalination of brackish water and wastewater by reverse osmosis. However, the interaction between inorganic silica species and dissolved organic molecules and their combined impact on membrane fouling are poorly understood. In this study, we have used sodium silicate and sodium alginate as model inorganic and organic foulants, respectively. Membrane fouling experiments showed a cooperative effect between the dissolved silica and alginate macromolecules, which aggravated membrane fouling. The molecular interactions between sodium alginate and sodium silicate and the properties of the formed complexes were determined by X-ray diffraction and X-ray photoelectron spectroscopy. Results show that the crystallinity of the formed complexes decreased as we increased the ratio of silica in the silica-alginate mixture, indicating the formation of amorphous complexes. Full reflection Fourier transform infrared spectroscopy also confirms new functional groups following the interaction between silica and alginate. Isothermal titration calorimetry was also employed to quantitatively determine the binding parameters by measuring the heat change during the reaction. When binding occurs between silica and alginate, the measured adsorbed or released heat is used to determine the binding constants as well as the enthalpy and entropy changes. Our results suggest that the interaction between silica and alginate is spontaneously exothermic and dominated by noncovalent bonding. Our findings provide fundamental insights into the complexation between silica and alginate in reverse osmosis membrane fouling and highlight the binding mechanism between silica and alginate molecules.

New insight into fate and fouling behavior of bulk Dissolved Organic Matter (DOM) in a full-scale membrane bioreactor for domestic wastewater treatment

Dissolved Organic Matter (DOM) and active biomass concentrations from a full-scale membrane bioreactor (MBR) treating domestic wastewater were investigated during a period of 488 days. Bulk DOM is known to be a major membrane foulant in MBR. Active biomass activity, which depends on operating parameter variations, is a major source of DOM, due to soluble microbial product (SMP) secretion. To establish the link between DOM, active biomass concentration, operating conditions, and later membrane fouling, heterotrophic and autotrophic bacteria were first quantified using respirometric measurements. Comparing their evolution with operating conditions and parameters using Principal Component Analysis (PCA), SRT and temperature were identified as the parameters with the most impact on active biomass concentrations. Proteins from Biopolymers and humic substance (HS + BB) concentrations were quantified using a 3DEEM pseudo-quantitative method. Active biomass and DOM concentration fluctuations were similar, confirming that DOM was mainly constituted by SMP produced by the active biomass, and consequently dependent on SRT and temperature modifications. HS + BB were produced eight times faster than Proteins from BP and therefore accumulated faster on the membrane despite their low membrane rejection. Consequently, large amounts of HS + BB can accumulate, modifying the initial membrane properties. The membrane resistance evolution was dependent on Proteins from Biopolymers accumulation and these molecules showed no fouling propensity modifications despite seasonal variations. As a consequence, this study strongly emphasized the interest of using a 3DEEM pseudo-quantitative method for on-line application in order to follow the full-scale MBR process and membrane fouling.

Dynamic membrane filtration using powdered iron oxide for SWRO pre-treatment during red tide event

Shut-down or reduced treated water supply of a seawater reverse osmosis (SWRO) plant due to membrane fouling during a red tide event is currently an important issue in regions where red tide frequently occurs. Algal organic matter (AOM) released by algae through metabolic activity is known as a major membrane foulant and the primary cause of the suspension of SWRO plants. In this study, iron oxide was utilized to develop an AOM removal process in seawater since activated carbon and advanced oxidation process (AOP) have limited removal efficiencies due to the high ionic strength of the seawater. Dynamic membrane filtration was applied as an iron oxide application method because additional process is not required for temporary operation during only algal bloom. The results showed that the dissolved organic carbon (DOC) removal efficiencies of the iron oxide were improved at high ionic strength compared to organics removal in fresh water. Although only a partial adsorption rate (below 50%) was achieved using iron oxide, significant reduction of the ultrafiltration (UF) membrane fouling was observed through the continuous operation of dynamic membrane filtration since relatively high molecular weight faction of organics was more readily adsorbed in the oxide surface. Given the continuous lab-scale experimental results and economic aspect, dynamic membrane filtration using powdered iron oxide can be a potential option as an emergency plan during a red tide event.

Treatment performance and membrane fouling characteristics of inclined-tube anoxic/aerobic membrane bioreactor applied to municipal solid waste leachate

This study investigated the performance of inclined tube anoxic/aerobic membrane bioreactor (itMBR) treating concentrated municipal solid waste leachate over 550 d at organic loading rates of 4.2–31.8 kg BOD/m3 d. At optimum loading of 18 kg BOD/m3 d, the itMBR could achieve high removals of 97% for biochemical oxygen demand, 94% for chemical oxygen demand, and 95% for total Kjeldahl nitrogen. Complete elimination of protein-like substances and partial removal of fulvic and humic acid-like substances were achieved. Major membrane foulants were found to be gel layers containing protein-like and polysaccharide-like substances and Ca-based inorganic scaling. Membrane cleaning using sodium hypochlorite followed by citric acid was found effective for the restoration of transmembrane pressure (TMP) while periodical chemical enhanced back-flushing at every 7–10 d could limit TMP increase rate and sustain the operation in long term.

Adsorption characteristics of Effluent Organic Matter and Natural Organic Matter by Carbon Based Nanomaterials

Natural Organic Matter (NOM) and Effluent Organic Matter (EfOM) have been regarded as the major membrane foulants in advanced water treatment or wastewater reuse processes. In this study, the adsorption of Suwannee River NOM (SRNOM) and EfOM from a wastewater treatment plant by Carbon-Based Nanomaterials (CBNs) including Single-Wall Carbon Nanotube (SWCNT), Multi-wall Carbon Nanotube (MWCNT) and Expanded Graphite (EG) was investigated to mitigate their membrane fouling potentials. Adsorption of SRNOM and EfOM showed Langmuir type adsorption with constant adsorption enthalpy, regardless of the adsorbents. MWCNT showed the highest adsorption capacity for SRNOM and EfOM, while SWCNT showed the greatest reduction in Soluble Microbial Products (SMP) in EfOM. The UV/Vis spectrophotometry, fluorescence spectrophotometry, and size exclusion chromatography showed that high molecular weight fraction of SRNOM and EfOM was preferentially adsorbed onto ordered CBNs such as SWCNT, MWCNT, and EG. It was also evidenced that SMP adsorptions by SWCNT was significantly higher than those by MWCNT. The results imply that a pretreatment with SWCNT or EG can reduce membrane fouling via adsorption of SMP and high molecular weight organic fractions in EfOM.

Identifying the major fluorescent components responsible for ultrafiltration membrane fouling in different water sources

Three-dimensional fluorescence excitation–emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) was performed for a total of 18 water samples taken from three water sources (two lakes and one wastewater treatment plant (WWTP) secondary effluent), with the purpose of identifying the major ultrafiltration (UF) membrane foulants in different water sources. Three fluorescent components (C1, C2 and C3) were identified, which represented terrestrially derived humic-like substances (C1), microbially derived humic-like substances (C2), and protein-like substances (C3). The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components (C1, C2 and C3) made a considerable contribution to the irreversible and total fouling of the UF membrane. However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes.

Identification of irreversible UF membrane foulants by fluorescence excitation–emission matrix coupled with parallel factor analysis

In this work, a total of nine water samples were taken from different water sources at different seasons for UF membrane fouling experiments, with the purpose to find out if there were common foulant components responsible for the irreversible membrane fouling. It was found that the increase in DOC and UV254 in raw water caused a corresponding increase in the developing rate of irreversible membrane fouling, demonstrating NOM as the major membrane foulants. Using the fluorescence excitation–emission matrices coupled with parallel factor analysis, four fluorescence components in NOM were identified, i.e. microbial-derived and terrestrial-derived humic-like substances (C1 and C3), tryptophan-like and tyrosine-like proteins (C2 and C4). The C2 exhibited a strong correlation with the irreversible fouling of UF membrane, while no correlation between C4 and irreversible membrane fouling was observed. The humic-like substances were shown to be weakly correlated to the irreversible membrane fouling. By multivariate linear regression, synergistic fouling effect was identified between the C2 and C3, but a comparison of their coefficients revealed that C2 made a considerably larger contribution to the irreversible membrane fouling than C3. The results may provide insights into the development of appropriate fouling control strategies for sustainable UF operation.

Random sequential adsorption of human adenovirus 2 onto polyvinylidene fluoride surface influenced by extracellular polymeric substances

Virus removal by membrane bioreactors depends on virus–membrane and virus–foulant interactions. The adsorption of human adenovirus 2 (HAdV-2) on polyvinylidene fluoride (PVDF) membrane and a major membrane foulant, extracellular polymeric substances (EPS), were measured in a quartz crystal microbalance. In 3–100mM CaCl2 solutions, irreversible adsorption of HAdV-2 was observed on both pristine and EPS-fouled PVDF surfaces. The HAdV-2 adsorption kinetics was successfully fitted with the random sequential adsorption (RSA) model. The applicability of the RSA model for HAdV-2 adsorption is confirmed by comparing the two fitting parameters, adsorption rate constant ka and area occupied by each adsorbed HAdV-2 particle a, with experimentally measured parameters. A linear correlation between the fitting parameter ka and the measured attachment efficiency was found, suggesting that the RSA model correctly describes the interaction forces dominating the HAdV-2 adsorption. By comparing the fitting parameter dads with the hydrodynamic diameter of HAdV-2, we conclude that virus–virus and virus–surface interactions determine the area occupied by each adsorbed HAdV-2 particle, and thus influence the adsorption capacity. These results provide insights into virus retention and will benefit improving virus removal in membrane filtration.

Effect of membrane polymeric materials on relationship between surface pore size and membrane fouling in membrane bioreactors

We investigated the effect of different membrane polymeric materials on the relationship between membrane pore size and development of membrane fouling in a membrane bioreactor (MBR). Membranes with different pore sizes were prepared using three different polymeric materials, cellulose acetate butyrate (CAB), polyvinyl butyral (PVB), and polyvinylidene fluoride (PVDF), and the development of membrane fouling in each membrane was evaluated by batch filtration tests using a mixed liquor suspension obtained from a laboratory-scale MBR. The results revealed that the optimal membrane pore size to mitigate membrane fouling differed depending on membrane polymeric material. For PVDF membranes, the degree of membrane fouling decreased as membrane pore size increased. In contrast, CAB membranes with smaller pores had less fouling propensity than those with larger ones. Such difference can be attributed to the difference in major membrane foulants in each membrane; in PVDF, they were small colloids or dissolved organics in which proteins are abundant, and in CAB, microbial flocs. The results obtained in this study strongly suggested that optimum operating conditions of MBRs differ depending on the characteristics of the used membrane.

Dewatering of Chlorella pyrenoidosa using diatomite dynamic membrane: Filtration performance, membrane fouling and cake behavior

The diatomite dynamic membrane (DDM) was utilized to dewater Chlorella pyrenoidosa of 2g dry weight/L under continuous-flow mode, whose ultimate algae concentration ranged from 43g to 22g dry weight/L of different culture time. The stable flux of DDM could reach 30L/m2h over a 24h operation time without backwash. Influences of extracellular organic matters (EOM) on filtration behavior and membrane fouling were studied. The DDM was divided into three sub-layers, the slime layer, the algae layer and the diatomite layer from the outside to the inside of the cake layer based on components and morphologies. It was found that EOM caused membrane fouling by accumulating in the slime and algae layers. The DDM intercepted polysaccharides, protein-like substances, humic-like substances and some low-MW organics. Proteins were indicated the major membrane foulants with increased protein/polysaccharide ratio from the slime layer to the diatomite layer as culture time increased. This method could be applied to subsequent treatment of microalgae coupling technology of wastewater treatment or microalgae harvesting for producing biofuel.

Correlations of relevant membrane foulants with UF membrane fouling in different waters

Correlations between potential fouling-relevant substances and membrane fouling during ultrafiltration (UF) of different waters were investigated, including water samples from Lake Tegel, from a Berlin canal (Landwehrkanal) and from a wastewater treatment plant (WWTP) secondary effluent. The biopolymers quantified with liquid chromatography-organic carbon detection (LC-OCD) showed a remarkable correlation with UF membrane fouling for all the three water sources at different seasons. This finding suggests that the biopolymer content in water can be employed as a universal indicator for predicting membrane fouling potential in UF processes. The particulate matter in the two surface waters Lake Tegel and Berlin canal, as characterized by suspended solids and turbidity, also exhibited a distinct correlation with UF membrane fouling, although its correlation was slightly weaker than that of biopolymers. However, the humic substances, which are generally believed to be major membrane foulants, did not show any reliable correlation with the UF membrane fouling of the different waters. This work may provide useful information for the development of optimized fouling control strategies for sustainable UF operation.

Chemical cleaning of ultrafiltration membrane fouled by an activated sludge effluent

In this study, membrane foulants and cleaning efficiency of different membrane cleaners for the ultrafiltration (UF) of a municipal activated sludge effluent were investigated. The major membrane foulants were polysaccharides, proteins, and humic substances (HS). Backwashing the fouled membrane removed some polysaccharides and proteins, but was not able to displace the adsorbed HS. Of the cleaners studied for the polyvinylidene fluoride (PVDF) UF membrane the most effective were sodium hypochlorite (200 ppm available chlorine), Terg-a-zyme (1.0 wt.%), and sodium dodecyl sulphate (10 mM). The results indicated that hydrophobic attraction was the most important force keeping the hydraulically irreversible foulants attached to the membrane. The surfaces of the fouled and cleaned membranes were analysed and interactions among the membranes, foulants, and the cleaning agents were discussed in terms of their chemistry and cleaning efficiency.

Fluorescence‐based fouling prediction and optimization of a membrane filtration process for drinking water treatment

AbstractA novel fluorescence‐based approach is proposed for modeling, predicting, and optimizing different fouling dynamics in an ultrafiltration (UF) process for drinking water treatment. Principal component analysis (PCA) was used to extract information in terms of principal components (PCs), related to major membrane foulant groups, from fluorescence excitation–emission matrix measurements captured during UF of natural river water. The evolution of PC scores during the filtration process was then related to membrane fouling using dynamic balances of latent variable values (PC scores). This approach was found suitable for forecasting fouling behaviors with good accuracy based solely on fluorescence data collected 15 min from the start of the filtration. The proposed approach was tested experimentally through model‐based optimization of backwashing times with the objective of minimizing the energy consumption per unit amount of water produced during the filtration process. This approach was also useful for identifying fouling groups contributing to reversible and irreversible fouling. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Effects of three natural organic matter types on cellulose acetate butyrate microfiltration membrane fouling

This study aimed to clarify the effect of interactions between membranes and natural organic matter (NOM), which is considered to be the major membrane foulant in wastewater treatment processes. Sodium alginate (SA), humic acid (HA) and bovine serum albumin (BSA) were used as NOM models. Hollow fiber membranes were prepared using cellulose acetate butyrate polymer (CAB). Filtration experiments were carried out using SA, HA and BSA solutions and the membrane fouling behavior was examined. NOM adsorption on CAB membranes was measured by quartz crystal microbalance with dissipation (QCM-D), where NOM solutions were flowed across CAB spin-coated quartz crystal sensors and adsorbed. SA showed more severe permeate flux decline during the early stage of filtration and lower recovery of permeate flux after backwashing compared with HA. The severe flux decline for SA was due to pore-plugging and cake formation with high molecular weight components. The BSA solution, with no high molecular components, showed a gradual permeate flux decline and resulted in lower permeate flux after 240 min filtration compared with HA. The gradual permeate flux decline with the BSA solution was due to ready adsorption of BSA on the CAB membrane.

Optimization of a Membrane Filtration Process for Drinking Water Production using On-line Fluorescence and Permeate Flux measurements

AbstractThe optimization of membrane filtration processes for controlling fouling is essential for the sustainable application of membrane processes in drinking water treatment applications. Natural organic matter (NOM) and colloidal/particulate matter are considered as the major membrane foulants and therefore their characterization is essential for implementing optimization strategies. In a previous work by the authors, a fluorescence-based modeling approach was developed for prediction of the fouling dynamics and for optimization of a bench-scale ultrafiltration (UF) membrane cross flow set-up for drinking water treatment. In this study, this model's predictive ability was improved by updating the model parameters based on current process measurements. The Extended Kalman Filter (EKF) approach was used to achieve this objective. The EKF approach was implemented to accomplish online-adaptive estimation of key model parameters based on either current (time = t) UF flux measurements or principal component (PC) scores related to current fluorescence measurements of membrane permeate. The model predictions and the corresponding experimental UF flux data of different membrane fouling situations revealed that on-line permeate flux-based parameter adaptation result in improved model predictions as compared to PC scores’ based adaptation. The resulting model based estimator was then employed in the optimization of the UF process in which membrane back-washing times were estimated in order to achieve minimum energy consumption while ensuring maximum production of drinking water.

Charge effect of natural organic matter for ultrafiltration and nanofiltration membranes

Natural organic matter (NOM) is one of the major membrane foulant during the ultrafiltration (UF) and nanofiltration (NF) processes of water and wastewater treatment. The purpose of this study is to determine the effect of membrane and NOM charge on NOM removal efficiency and membrane fouling. Fractions of NOM including colloidal organic matter (COM), hydrophobic NOM (HP-NOM) and transphillic NOM (TL-NOM) were isolated from Nakdong river in Korea and filtered through UF and NF membranes under various pH conditions to control membrane and NOM charge using the bench-scale cross-flow filtration unit. Each NOM fraction has a different size and functionality. Each UF and NF charge affected NOM removal and membrane fouling. Membrane charge of UF affected both membrane fouling and NOM removal of charged NOM and non-charged NOM. However, membrane charge of NF affected both membrane fouling and NOM removal efficiency of charged NOM while it was not influenced by that of non-charged NOM.

Membrane foulants and fouling mechanisms in microfiltration and ultrafiltration of an activated sludge effluent

Membrane fouling in microfiltration (MF) and ultrafiltration (UF) of an activated sludge (AS) effluent was investigated. It was found that the major membrane foulants were polysaccharides, proteins, polysaccharide-like and protein-like materials and humic substances. MF fouling by the raw effluent was governed by pore adsorption of particles smaller than the pores during the first 30 minutes of filtration and then followed the cake filtration model. UF fouling could be described by the cake filtration model throughout the course of filtration. Coagulation with alum and (poly)aluminium chlorohydrate (ACH) altered the MF fouling mechanism to follow the cake filtration model from the beginning of filtration. The MF and UF flux improvement by coagulation was due to the removal of some of the foulants in the raw AS effluent by the coagulants. The MF flux improvement was greater for alum than for ACH whereas the two coagulants performed equally well in UF. Coagulation also reduced hydraulically irreversible fouling on the membranes and this effect was more prominent in MF than in UF. The unified membrane fouling index (UMFI) was used to quantitatively evaluate the effectiveness of coagulation on membrane flux enhancement.