•Membrane fouling by combined ozone and PAC pretreatment was evaluated.•The combined treatment at higher ozone doses gave a substantially potential on TMP control.•Macro molecules biopolymers had high correlations with TMP/TMP0 increase.This work investigates the effects of combined ozone and powered activated carbon (PAC) pretreatment on ultrafiltration (UF) performance. High performance size exclusion chromatography (HPSEC) combined with peak-fitting prediction and fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis (EEM-PARAFAC) were used to analyze membrane fouling and organic removal. We conclude that combined ozone and PAC pretreatment can significantly inhibit an increase in transmembrane pressure (TMP) whereby ozone plays a predominant role in delaying TMP increases. Ozone and activated carbon can greatly improve the removal efficiency of organic matter, especially that of macromolecular biopolymers, medium molecules of humic-like substances and small molecular acids and neutrals; however, the removal efficiency of aromatic proteins containing tyrosine is limited. Macromolecular biopolymers show high correlations with TMP/TMP0, followed by that of building blocks of low molecular acids and neutrals, while humic-like substances have a minor influence on UF membrane fouling. Fluorescence EEM is not valid for use as an indicator of membrane fouling after combined ozone and PAC treatment according to this study.Download high-res image (179KB)Download full-size image

•Blocking models and interaction energy theory were employed to evaluate PAC alleviating membrane fouling.•Cake formation was the major mechanism of membrane fouling.•PAC pre-treated water had a relatively low fouling rate.•PAC enhanced the removal of NEU and SHA (based on fractionation), and BB&LMW-A (based on HPSEC).•PAC could control membrane fouling through decreasing AB interaction energy.The mechanism of powdered activated carbon (PAC) mitigating microfiltration (MF) membrane fouling for surface water treatment was investigated via blocking models, resin adsorption fractionation, high performance size exclusion chromatography (HPSEC) with peak-fitting, and interaction free energy theory. The results identified cake formation as the major mechanism of membrane fouling. Also, PAC pre-treated water showed a relatively lower fouling rate than untreated raw water and PAC had a positive effect on improving membrane flux on account of the enhanced removal of neutral hydrophilic compounds (NEU) and strongly hydrophobic acids (SHA) (based on fractionation), and building blocks and low molecular weight acids (BB&LMW-A) (based on HPSEC). Analysis of the interfacial energy between membrane and foulants via the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory found that AB interaction energy played a dominating role in the components of interaction free energies during MF process. PAC, by decreasing AB interaction energy, could thus control membrane fouling.Download high-res image (172KB)Download full-size image

In this study, membrane fouling and the mechanism of algal extracellular organic matter (EOM) due to various trace heavy metals (iron) during ultrafiltration (UF) was investigated in detail. In both early and late exponential growth phases, the results indicated that the membrane fouling caused by EOM at low iron concentrations in this study was more severe than that at high and normal iron concentrations. Low iron concentrations produced the highest total (R) and reversible fouling resistance (Rre), of which Rre was higher, followed by membrane resistance (Rm), and irreversible fouling resistance (Rir). The analysis of EOM characteristics indicated that low iron in this study stimulated the growth of algae beyond high and normal iron concentrations, including increases in chlorophyll a; protein (tryptophan-like and tyrosine-like organic matter) content; and macro, medium and small molecular organic matters. Humic-like organics were more synthesized under high iron concentrations. Analyses of membrane fouling behavior illustrated that cake formation was the major fouling mechanism for the three iron concentrations, and it accounted for a greater proportion of fouling in the low iron concentration than in the other two iron concentrations; cake resistance played a more critical role in the late exponential growth phase than in the primary exponential phase.Download high-res image (203KB)Download full-size image

•PAC pre-treated water had a relatively low FRs and FIs.•PAC preferentially adsorbed LMWA&BB as well as HS fractions.•PCA was used to identify fouling behavior associated with water characteristics.•LMWA&BB imparted great contribution to membrane fouling.•PAC controlling fouling was attributed to the reduction of LMWA&BB.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.

•Fouling behavior of APF- and ANF-AOM fractions were analyzed by the XDLVO theory.•N-HPI and HPO were more easily attached to membranes for cake formation.•Interfacial energy between N-HPI and N-HPI fractions was the biggest contributor to membrane fouling.Fouling caused by algogenic organic matter (AOM) in membrane filtration is a critical problem in algae-rich waters, and understanding fouling mechanisms, particularly by identifying the predominant membrane foulants, could have significant effects on algal fouling prediction and pretreatment. In this work, the fouling behavior of Aphanizomenon flos-aquae (APF)- and Anabaena flos-aquae (ANF)-AOM fractions was analyzed using the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The results show that the interfacial energy of membranes and foulants could be used for AOM membrane fouling analysis. The attractive energy was highest between the membrane and the neutral hydrophilic fractions (N-HPI) on clean membrane surfaces, followed by the energy associated with the hydrophobic fractions (HPO) and the transphilic fractions (TPI) in both of the AOMs; on the other hand, the negatively charged hydrophilic organics (C-HPI) in the APF-AOM suffered from repulsive interactions when nearing the membrane surface, which was consistent with their initial filtration flux. After the formation of an initial fouling layer on the membrane surface, membrane fouling was controlled mainly by the cohesion free energy between the approaching foulants and the foulants on the fouled membranes. In addition, it was observed that the interfacial energy between foulants was the dominant factor controlling membrane fouling in AOM filtration. Finally, the interfacial energies between the N-HPI fractions had the greatest effect on both APF-AOM and ANF-AOM membrane fouling.

A flat submerged membrane combined with a TiO2/UV photocatalytic reactor (FSMPR) was employed in batch mode to remove humic acid (HA). HA removal efficiency was characterized by UV254 absorbance, UV-vis spectra, dissolved organic carbon (DOC) concentration, specific UV absorbance (SUVA), and trihalomethane formation potential (THMFP). The FSMPR process was effective in removing more than 86% of DOC and nearly 100% of UV254 absorbance, while the THMFPs of samples were reduced to < 19 μg/L after 150 min of treatment. In addition, changes in transmembrane pressure (TMP) with and without UV were evaluated; TiO2/UV was effective at controlling membrane fouling by HA. Analysis of the molecular weight (MW) distributions and three-dimensional excitation-emission matrix (EEM) fluorescence spectra of HAs revealed that the effectiveness in membrane fouling control is a result of changes in HA molecular characteristics. The TiO2/UV photocatalytic reactor caused the degradation of high MW, hydrophobic humic-like molecules to low MW, hydrophilic protein-like molecules, although this fraction was not completely removed during 150 min of treatment and was less responsible for membrane fouling.

The bio-diatomite dynamic membrane (BDDM) reactor is an emerging micro-polluted surface water treatment technology that combines diatomite (the microorganism carrier) and a stainless steel mesh (the dynamic membrane support module). A constant water head of 20 cm was designed to drive the BDDM filtration. The BDDM with sintered diatomite had good water penetration capacity, a filtration flux as high as 92 L/m2 h after a filtration time of 15,780 min, and an effluent turbidity in the range of 0.15 NTU–0.20 NTU. The BDDM reactor effectively removed organic matter and ammonium nitrogen. The diatomite adsorption and the BDDM interception did not have high pollutant removal efficiencies. The dehydrogenase activity (DHA) of the bio-diatomite was in the range of 2.27–3.20 (mg TF)/(gVSS) h, indicating good microorganism activity for organic matter removal. The PCR-DGGE analysis showed that the microbial community was very abundant. Bacteroidetes, Firmicutes, Proteobacteria (e.g. α-, β-, γ-proteobacteria), Verrucomicrobia, and Nitrospirae were dominant in the bio-diatomite mixed liquor and removed organic matter and ammonium nitrogen. The microbial degradation of pollutants by the bio-diatomite mixed liquor was primarily responsible for the pollutant removal in the BDDM reactor.Highlights► The BDDM filtration was driven by the 20 cm water head. ► The BDDM can be operated successfully with high filtration flux. ► Microbial degradation was the main pollutant removal mechanism in the BDDM reactor.

This work investigated the characteristics of algogenic organic matter (AOM) that was produced by blue-green algae grown under different nitrogen to phosphorus ratios (1N:1P, 1N:2P, 1N:10P, 2N:1P). Subsequently, the potential for AOM microfiltration (MF) membrane fouling under these scenarios was evaluated. The results showed that algae grew differently under various N/P ratios. Microcystis aeruginosa in 1N:10P and 1N:2P grew much better than those in 1N:1P. When constant phosphorous concentrations were maintained, no obvious effect was observed on the accumulation of algal intracellular organic matter. The amount of AOM released from M. aeruginosa was also affected by the N/P. AOM fraction analysis showed that the neutral hydrophilic fraction (N-HPI) was the main component of AOM; with lower N/P ratios, the proportion of hydrophilic AOM increased. Moreover, molecular weight (MW) distribution discrepancies existed among different AOMs. MF membrane fouling by AOM may also be influenced by N/P variations. AOM at 1N:10P exerted the strongest impact on membrane fouling, followed sequentially by 1N:2P, 1N:1P and 2N:1P. According to the analysis of the excitation–emission matrices (EEMs) and the MW distribution of membrane filtration, the membrane fouling potential of AOM seemed to be mainly associated with polysaccharide-like or protein-like substances of large MW.Highlights► Nutrients have significant effects on the growth of Microcystis aeruginosa. ► Characteristics of algogenic organic matter influenced by various N/Ps were investigated. ► Microfiltration membrane fouling by AOM under N/P variations was examined.

•Membrane fouling caused by different algogenic organic matters varied significantly.•Two sets of membrane fouling mechanisms were proposed in AOM MF.•Surface free energy of membranes and foulants was used to analyze membrane fouling.This paper systematically investigated the microfiltration membrane fouling behavior of various algogenic organic matters (AOMs) that were extracted from five classical bloom algae (cyanobacteria, green algae and diatoms). The results indicated that membrane fouling by different algae varied significantly by algal species and AOM chemical compositions. Cyanobacteria of the species Aphanizomenon flos-aquae (APF)-AOM caused the strongest flux decline, followed by Anabaena flos-aquae (ANF)- and Microcystis aeruginosa (MA)-AOMs. Analysis of AOM characteristics indicated that the membrane fouling depended on the synergies that arose from specific combinations of fluorescence excitation–emission matrix (EEM), molar sizes and/or membrane material properties. By applying the extended version of Derjaguin Landau Verwey Overbeek (XDLVO) theory, it was found that the cohesion free energies and the adhesion free energies between APF-, ANF-, and MA-AOMs and each of the membranes were more negative than those between membranes and the green algae and the diatoms of Scenedesmus obliquus (SO)- and Cyclotella (Cy)-AOMs; more negative energies indicate that the attraction forces are much stronger and can cause heavier membrane fouling. SO-AOM and Cy-AOM have less negative cohesion free energies and adhesion free energies with the membranes, and there was less membrane fouling with those AOMs. The surface free energy of membranes and foulants is a useful parameter for membrane fouling analysis.Download full-size image

•Combined membrane process was investigated to cope with algae bloom water.•Algae bloom in this study did not affect membrane filtration operation.•PAC and KMnO4 prolonged the cycle of filtration.•Medium and small MW of HPO and N-HPI caused irreversible fouling.Algae blooms seriously threaten water quality and the supply of drinking water. A membrane process combined with coagulation, powdered activated carbon, and potassium permanganate was used as a treatment and investigated for its ability to cope with algae blooms in water bodies. The experimental results demonstrated that algae blooms can cause greater organic matter concentrations with large increases in the small neutral hydrophilic fraction (molecular weight (MW) lower than 1000 Da). This organic matter was effectively removed by pretreatment; therefore, no serious impacts on membrane filtration operation were found. Powdered activated carbon and potassium permanganate prolonged the filtration cycle. By investigating the fouled membranes during microfiltration (MF), we determined that the organics responsible for irreversible membrane fouling included strong hydrophobic and neutral hydrophilic organics with medium and small MWs, especially protein and carbohydrate in the neutral hydrophilic fraction. Alkaline cleaning was more efficient for organic elution than acidic cleaning; however, the acidic agent desorbed protein more effective than the alkaline agent.

•Macroporous anion resin was used to treat NOM in low pressure membrane.•Macroporous anion resin treatment alleviates membrane fouling to some extent.•Integrated PAC and resin pretreatment were efficient in membrane fouling control.Macro-porous anion exchange, coagulation and their combination were used as pretreatment for microfiltration, and their effects on organic removal and membrane fouling reduction were evaluated. The experimental results showed that resin was effective in removing organics of medium and small molecular weight (MW), especially those of medium MW of UV absorbance, but was ineffective in removing organics with large MW. Using resin alone as a pretreatment removed organics effectively but was limited in its reduction of membrane fouling. With the combination of coagulation and resin as a pretreatment for microfiltration, not only were organics removed effectively, but membrane fouling was also reduced. Analysis of membrane surface with scanning electron microscopy (SEM), atomic force microscopy (AFM) and combined results of behaviors of MW distribution and flux indicated that biopolymer plays a key role in membrane fouling, and coagulation could remove this part of organics. Integrated coagulation and resin pretreatment by filtration columns were suggested for use in surface water prior to membrane filtration.Download full-size image