Control of chlorination disinfection by-products in drinking water by combined nanofiltration process: A case study with trihalomethanes and haloacetic acids.

Disinfection by-products (DBPs) are prevalent contaminants in drinking water and are primarily linked to issues regarding water quality. These contaminants have been associated with various adverse health effects. Among different treatment processes, nanofiltration (NF) has demonstrated superior performance in effectively reducing the levels of DBPs compared to conventional processes and ozone-biological activated carbon (O3-BAC) processes. In this experiment, we systematically investigated the performance of three advanced membrane filtration treatment schemes, namely "sand filter + nanofiltration" (SF + NF), "sand filter + ozone-biological activated carbon + nanofiltration" (SF + O3-BAC + NF), and "ultrafiltration + nanofiltration" (UF + NF), in terms of their ability to control disinfection by-product (DBP) formation in treated water, analyzed the source and fate of DBP precursors during chlorination, and elucidated the role of precursor molecular weight distribution during membrane filtration in relation to DBP formation potential (DBPFP). The results indicated that each treatment process reduced DBPFP, as measured by trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP), with the SF + O3-BAC + NF process being the most effective (14.27 µg/L and 14.88 µg/L), followed by the SF + NF process (21.04 µg/L and 16.29 µg/L) and the UF + NF process (26.26 µg/L and 21.75 µg/L). Tyrosine, tryptophan, and soluble microbial products were identified as the major DBP precursors during chlorination, with their fluorescence intensity decreasing gradually as water treatment progressed. Additionally, while large molecular weight organics (60-100,000 KDa) played a minor role in DBPFP, small molecular weight organics (0.2-5 KDa) were highlighted as key contributors to DBPFP, and medium molecular weight organics (5-60 KDa) could adhere to the membrane surface and reduce DBPFP. Based on these findings, the combined NF process can be reasonably selected for controlling DBP formation, with potential long-term benefits for human health.

Alleviating Ultrafiltration Membrane Fouling Caused by Effluent Organic Matter Using Pre-Ozonation: A Perspective of EEM and Molecular Weight Distribution.

Wastewater reclamation has gradually become an important way to cope with the global water crisis. Ultrafiltration plays an imperative part as a safeguard for the aim but is often limited by membrane fouling. Effluent organic matter (EfOM) has been known to be a major foulant during ultrafiltration. Hence, the primary aim of this study was to investigate the effects of pre-ozonation on the membrane fouling caused by EfOM in secondary wastewater effluents. In addition, the physicochemical property changes of EfOM during pre-ozonation and the subsequent influence on membrane fouling were systemically investigated. The combined fouling model and the morphology of fouled membrane were adopted to scrutinize the fouling alleviation mechanism by pre-ozonation. It was found that membrane fouling by EfOM was dominated by hydraulically reversible fouling. In addition, an obvious fouling reduction was achieved by pre-ozonation with 1.0 mg O3/mg DOC. The resistance results showed that the normalized hydraulically reversible resistance was reduced by ~60%. The water quality analysis indicated that ozone degraded high molecular weight organics such as microbial metabolites and aromatic protein and medium molecular weight organics (humic acid-like) into smaller fractions and formed a looser fouling layer on the membrane surface. Furthermore, pre-ozonation made the cake layer foul towards pore blocking, thereby reducing fouling. In addition, there was a little degradation in the pollutant removal performance with pre-ozonation. The DOC removal rate decreased by more than 18%, while UV254 decreased by more than 20%.

Investigation of membrane fouling and mechanism induced by extracellular organic matter during long-term exposure to pharmaceuticals and personal care products.

This study investigated ultrafiltration membrane fouling by extracellular organic matter (EOM) and the mechanism operating during long-term exposure to pharmaceuticals and personal care products. The results indicated that carbamazepine and diclofenac in algal-laden water altered the filtration flux and membrane fouling by EOM. Exposure to low-concentration carbamazepine (0.25 µg/L) improved the filtration flux and the total (Rtot) and reversible fouling resistance (Rc), whereas the filtration flux and Rtot and Rc were reduced when EOM was used during long-term exposure to high carbamazepine concentrations (>1 µg/L). Both Rtot and Rc were increased when algae were exposed to 0.25 µg/L diclofenac, whereas the filtration flux and Rtot and Rc were alleviated when algae were exposed to >1 µg/L diclofenac. Moreover, carbamazepine and diclofenac (0.25 µg/L - 1000 µg/L) in water enhanced the irreversible fouling resistance (Rb) when ultrafiltration was used to treat algal-laden waters. The mechanism indicated that membrane fouling induced by standard blocking was transformed to complete blocking when EOM was exposed to high levels of carbamazepine (>0.25 µg/L) in the initial filtration process, whereas cake layer formation played an important role during the later filtration process; with low carbamazepine levels (0.25 µg/L), standard blocking of EOM was dominant during the entire filtration process. The membrane fouling mechanism also changed when algal-laden waters were exposed to diclofenac, the membrane fouling was transformed from complete blocking to standard blocking when DFC was present in the initial filtration process, whereas cake layer formation exerted an important role during the late filtration process. This research provides important information on the long-term risks caused by pharmaceutical and personal care products and potential threats to membrane treatment.

PAC-UF Process Improving Surface Water Treatment: PAC Effects and Membrane Fouling Mechanism.

In this study, the water purification effect and membrane fouling mechanism of two powdered activated carbons (L carbon and S carbon) enhancing Polyvinylidene Fluoride (PVDF) ultrafiltration (UF) membranes for surface water treatment were investigated. The results indicated that PAC could effectively enhance membrane filtration performance. With PAC addition, organic removal was greatly enhanced compared with direct UF filtration, especially for small molecules, i.e., the S-UF had an additional 25% removal ratio of micro-molecule organics than the direct UF. The S carbon with the larger particle size and lower specific surface area exhibited superior performance to control membrane fouling, with an operation duration of S-UF double than the direct UF. Therefore, the particle size and pore structure of carbon are the two key parameters that are essential during the PAC-UF process. After filtration, acid and alkaline cleaning of UF was conducted, and it was found that irreversible fouling contributed the most to total filtration resistance, while the unrecoverable irreversible resistance ratio with acid cleaning was greater than that with alkaline cleaning. With PAC, irreversible UF fouling could be relieved, and thus, the running time could be extended. In addition, the membrane foulant elution was analyzed, and it was found to be mainly composed of small and medium molecular organic substances, with 12% to 21% more polysaccharides than proteins. Finally, the hydrophilicity of the elution was examined, and it was observed that alkaline cleaning mainly eluted large, medium, and small molecules of hydrophilic and hydrophobic organic matter, while acid cleaning mainly eluted small molecules of hydrophilic organic matter.

Fate, mobility, and pathogenicity of drinking water treatment plant resistomes deciphered by metagenomic assembly and network analyses.

Antibiotic resistance genes (ARGs) have been regarded as emerging environmental contaminants. The profile of resistome (collection of all ARGs) in drinking water and its fate during drinking water treatment remain unclear. This study applied metagenomic assembly combined with network analysis to decipher the profile, mobility, host, and pathogenicity of resistomes in two full-scale drinking water treatment plants (DWTPs), each applying conventional treatment and advanced treatment of ozonation followed by biological activated carbon filtration. In source waters and effluents of each treatment process collected from both DWTPs, 215 ARGs belonging to 20 types were detected with total concentration ranging from 6.30 ± 1.83 to 5.20 ± 0.26 × 104 copies/mL. Both the conventional and advanced DWTPs were revealed to effectively reduce the concentration of total ARGs, with the average removal efficiency of 3.61-log10 and 2.21-log10, respectively. Multiple statistical analyses (including network analysis) indicated drinking water resistome correlated tightly with mobile gene elements (MGEs) and bacterial community, with the latter acting as the premier driver of resistome alteration in DWTPs. Further analysis of ARG-carrying contigs (ACCs) assembled from drinking water metagenomes (i) tracked down potential bacterial hosts of ARGs (e.g., Proteobacteria phylum as the major pool of resistome), (ii) provided co-localization information of ARGs and MGEs (e.g., MacB-E7196 plasmid1), and (iii) identified ARG-carrying human pathogens (e.g., Enterococcus faecium and Ralstonia pickettii). This work firstly determined the concentration, mobility incidence, and pathogenicity incidence of DWTP resistomes, based on which the actual health risk regarding antibiotic resistance could be quantitatively assessed in further study, providing a useful direction for decision-making concerning the risk control of ARGs in DWTPs.

Diatomite Dynamic Membrane Fouling Behaviour during Dewatering of Chlorella pyrenoidosa in Aquaculture Wastewater.

Combined microalgal and membrane filtration could effectively treat aquaculture wastewater; however, the membrane fouling induced by extracellular organic matter (EOM) during the dewatering process is an issue. This study investigated diatomite dynamic membrane (DDM) fouling behaviour during the dewatering of Chlorella pyrenoidosa under the influence of copper ions. The results indicate that copper ion heavy metals in aquaculture wastewater significantly affected purification and algae dewatering by DDM. Aquaculture wastewater with a high copper concentration (1 and 0.5 mg/L) could induce serious DDM fluxes and cake layer filtration resistance (Rc), whereas fewer filtration fluxes were induced when aquaculture wastewater had a low copper concentration, particularly that of 0.1 mg/L, at which the Rc was lowest and the concentration effect was highest. Macromolecular organics of EOM, such as biopolymers, polysaccharides, and proteins, were responsible for DDM fouling and accumulated mostly in the slime layer, whereas only a small amount of them accumulated in the diatomite layer. The DDM rejected more protein-like organics of EOM in the slime layer when dewatering algae at low copper concentrations (<0.1 mg/L); however, when using the DDM to dewater algae at high copper concentrations, more polysaccharides of EOM were rejected (0.5 < Cu2+ < 5 mg/L). This result has significant ramifications for aquaculture wastewater treatment as well as algae separation and concentration by the DDM.

Application of Coagulation-Membrane Rotation to Improve Ultrafiltration Performance in Drinking Water Treatment.

The combination of conventional and advanced water treatment is now widely used in drinking water treatment. However, membrane fouling is still the main obstacle to extend its application. In this study, the impact of the combination of coagulation and ultrafiltration (UF) membrane rotation on both fouling control and organic removal of macro (sodium alginate, SA) and micro organic matters (tannic acid, TA) was studied comprehensively to evaluate its applicability in drinking water treatment. The results indicated that membrane rotation could generate shear stress and vortex, thus effectively reducing membrane fouling of both SA and TA solutions, especially for macro SA organics. With additional coagulation, the membrane fouling could be further reduced through the aggregation of mediate and macro organic substances into flocs and elimination by membrane retention. For example, with the membrane rotation speed of 60 r/min, the permeate flux increased by 90% and the organic removal by 35% in SA solution, with 40 mg/L coagulant dosage, with an additional 70% increase of flux and 5% increment of organic removal to 80% obtained. However, too much shear stress could intensify the potential of fiber breakage at the potting, destroying the flocs and resulting in the reduction of permeate flux and deterioration of effluent quality. Finally, the combination of coagulation and membrane rotation would lead to the shaking of the cake layer, which is beneficial for fouling mitigation and prolongation of membrane filtration lifetime. This study provides useful information on applying the combined process of conventional coagulation and the hydrodynamic shear force for drinking water treatment, which can be further explored in the future.

Pilot Study on the Combination of Different Pre-Treatments with Nanofiltration for Efficiently Restraining Membrane Fouling While Providing High-Quality Drinking Water.

Nanofiltration (NF) is a promising post-treatment technology for providing high-quality drinking water. However, membrane fouling remains a challenge to long-term NF in providing high-quality drinking water. Herein, we found that coupling pre-treatments (sand filtration (SF) and ozone-biological activated carbon (O3-BAC)) and NF is a potent tactic against membrane fouling while achieving high-quality drinking water. The pilot results showed that using SF+O3-BAC pre-treated water as the feed water resulted in a lower but a slowly rising transmembrane pressure (TMP) in NF post-treatment, whereas an opposite observation was found when using SF pre-treated water as the feed water. High-performance size-exclusion chromatography (HPSEC) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy determined that the O3-BAC process changed the characteristic of dissolved organic matter (DOM), probably by removing the DOM of lower apparent molecular weight (LMW) and decreasing the biodegradability of water. Moreover, amino acids and tyrosine-like substances which were significantly related to medium and small molecule organics were found as the key foulants to membrane fouling. In addition, the accumulation of powdered activated carbon in O3-BAC pre-treated water on the membrane surface could be the key reason protecting the NF membrane from fouling.

The role of carbonate radicals on the kinetics, radical chemistry, and energy requirement of UV/chlorine and UV/H2O2 processes.

Quantitative insight into the HCO3--dependent degradation kinetics is critical to improve understanding of the UV processes for the most-cost effective application. In this study, we developed a kinetic model to precisely predict the kinetics in UV/H2O2 and UV/chlorine processes. The second-order rate constants of HO, Cl, ClO, Cl2-, and CO3- with carbamazepine (CBZ) were fitted as 1.3 × 109, 1.9 × 109, 1.8 × 106, 1.1 × 105, and 4.5 × 106 M-1 s-1, respectively. Based on the model, we investigated the significant impact of bicarbonate (HCO3-) and subsequently generated carbonate radical (CO3-) on CBZ degradation, radical chemistry, and energy requirement of UV/H2O2 and UV/chlorine processes. The presence of HCO3- inhibited CBZ degradation in UV/H2O2 and UV/chlorine processes to different degree. Contributions of HO, Cl, ClO, Cl2-, and CO3- to CBZ degradation in UV/H2O2 and UV/chlorine processes in the absence/presence of HCO3- were investigated. HO and CO3- make comparable contributions to CBZ degradation in UV/H2O2 process in the presence of HCO3- (2 mM), while ClO is always the main contributor at various HCO3- concentration of 0-2 mM. Furthermore, the presence of HCO3- in both processes increased the corresponding EE/O, when CBZ was degraded by an order of magnitude. Overall, HCO3- and CO3- influence the reactions and mechanism of UV/H2O2 and UV/chlorine processes, and have higher impact on UV/H2O2 process.

Natural organic matter separation by forward osmosis: Performance and mechanisms.

The purification performance of a forward osmosis (FO) membrane on natural organic matter (NOM) contained in real surface water by was investigated systematically. FO could reject the natural dissolved organic matter (DOM) effectively with removal efficiencies of approximately 99.0%. When the natural water samples (e.g., raw surface water) had lower fouling tendencies, the active layer facing the draw solution (AL-facing-DS mode) provided a higher water flux than that in the alternative membrane orientation because the isoflux point occurred later in the process. It was found that the concentration of calcium ions had a more severe effect on decreasing the fouling flux of the FO membrane than that of the organic foulant. Furthermore, the concentrated feed solution had a more significant effect on the fouling flux decline of the natural DOM containing more small molecules than natural DOM containing more macromolecules. Additionally, the fouling that occurred in the AL-facing-DS orientation was compensated by the reduced internal concentration polarization (ICP) level based on the occurrence of the critical compensation point. It was also revealed that the permeation drag caused by the water flux and the chemical interactions induced by the feed solution pH and the calcium ion concentration played a significant role in the adsorption of small natural DOM molecules in the porous structure of the FO membrane. Based on the analysis of the interfacial free energies, the interactions between the natural DOM and the surface of the support layer dominated the initial fouling of the FO membrane, while subsequent fouling was controlled by the interaction between the approaching DOM molecules and the already adsorbed DOM.

Investigation of membrane fouling mechanism of intracellular organic matter during ultrafiltration.

This study investigated the ultrafiltration (UF) membrane fouling mechanism of intracellular organic matter (IOM) from Chlorella vulgaris (CV) and Microcystis aeruginosa (MA). Both CV- and MA-IOM caused severe membrane fouling during UF; however, there were significant differences in the membrane fouling by these two materials. Neutral hydrophilic (N-HPI) compounds were the organics that caused the most severe membrane fouling during CV-IOM filtration, whereas the MA-IOM membrane fouling was induced by mainly hydrophobic (HPO) organics. From an analysis based on Derjaguin-Landau-Verwey-Overbeek theory, it was found that the interaction energy between the membrane and foulants in the later stage of filtration was the major factor determining the efficiency of filtration for both CV-IOM and MA-IOM. The TPI organics in CV-IOM fouled the membrane to a more severe degree during the initial filtration flux; however, when the membrane surface was covered with CV-IOM foulants, the N-HPI fraction of CV-IOM caused the most severe membrane fouling because its attractive energy with the membrane was the highest. For MA-IOM, regardless of the initial filtration flux or the late stage of filtration, the HPO organics fouled the membrane to the greatest extent. An analysis of modified filtration models revealed that cake layer formation played a more important role than other fouling mechanisms during the filtration of CV-IOM and MA-IOM. This study provides a significant understanding of the membrane fouling mechanism of IOM and is beneficial for developing some strategies for membrane fouling control when treating MA and CV algae-laden waters.

Reversible and irreversible membrane fouling in hollow-fiber UF membranes filtering surface water: effects of ozone/powdered activated carbon treatment.

This study investigated the reversible and irreversible membrane fouling behavior of micro polluted water by ozone/powdered activated carbon (PAC)/ultrafiltration treatment. The results indicated that PAC mainly adsorbed low-molecular weight organics and reduced the irreversible fouling resistance in ultrafiltration, while there existed a threshold PAC dosage for total and reversible fouling resistance alleviation. Ozone at low doses exerted little effect on membrane fouling alleviation, while higher doses controlled total and reversible fouling by reducing macromolecular biopolymers and humic-like substances. Combined ozone and PAC pretreatment had greater effects on both reversible and irreversible fouling reduction than individual PAC and ozone treatment, demonstrating synergistic effects in the reduction of organic content in the feed water, including macromolecular biopolymers, humic-like, low-molecular weight neutral and building blocks. Backwashing and chemical cleaning analysis revealed that biopolymers and humic-like substances were the main organics that caused hydraulic reversible fouling, whereas low-molecular organics of building blocks and neutral, as well as humic-like substances were the main components that caused hydraulic irreversible fouling. Combined ozone and PAC treatment not only improved the backwashing efficiency but also reduced the membrane fouling during backwashing, as well as reversible and irreversible fouling. The cake layer formation and standard pore blocking were the major mechanisms for ultrafiltration membrane fouling, of which standard pore blocking exerted more important effects in the membrane fouling formation and alleviation by individual and combined PAC and ozone treatment.

Performance of Layer-by-Layer-Modified Multibore® Ultrafiltration Capillary Membranes for Salt Retention and Removal of Antibiotic Resistance Genes.

Polyether sulfone Multibore® ultrafiltration membranes were modified using polyelectrolyte multilayers via the layer-by-layer (LbL) technique in order to increase their rejection capabilities towards salts and antibiotic resistance genes. The modified capillary membranes were characterized to exhibit a molecular weight cut-off (at 90% rejection) of 384 Da. The zeta-potential at pH 7 was -40 mV. Laboratory tests using single-fiber modified membrane modules were performed to evaluate the removal of antibiotic resistance genes; the LbL-coated membranes were able to completely retain DNA fragments from 90 to 1500 nt in length. Furthermore, the pure water permeability and the retention of single inorganic salts, MgSO4, CaCl2 and NaCl, were measured using a mini-plant testing unit. The modified membranes had a retention of 80% toward MgSO4 and CaCl2 salts, and 23% in case of NaCl. The modified membranes were also found to be stable against mechanical backwashing (up to 80 LMH) and chemical regeneration (in acidic conditions and basic/oxidizing conditions).

Application of coagulation-ultrafiltration-nanofiltration in a pilot study for Tai Lake water treatment.

In this study, the inline coagulation was combined with ultrafiltration and nanofiltration (UF-NF) in a pilot study for Tai Lake water treatment. The results showed that the combination process was very effective for Tai Lake water treatment in terms of organic removal and membrane fouling control. With inline coagulation, no irreversible membrane fouling was observed for either UF or NF at fluxes of 65-90 and 22-26 L/(m2  hr), respectively. The membrane foulants were analyzed, and the results indicated that the low molecular weight fractions in the feed were main membrane fouling contributors for both UF and NF, where hydrophilic substances and proteins, as well as neutral substances and humic acids with polycarboxyl groups, contributed significantly to UF and NF membrane fouling, respectively. Compared with direct UF-NF filtration without coagulation, the coagulants could aggregate organic micromolecules for cake formation. With inline coagulation, the moving flocs could generate shear stress to scrub the membrane surface for fouling control of UF. Moreover, with inline coagulation, the organics removal efficiency could be further increased by 10%-20%. With NF, the permeate had a TOC concentration of less than 0.5 mg/L, satisfying the drinking water quality. Therefore, the coagulation-UF-NF is very useful for Tai Lake water treatment. PRACTITIONER POINTS: Inline coagulation-UF-NF for Tai Lake Water treatment is implemented. Inline coagulation can aggregate hydrophilic substances to reduce membrane fouling. Moving flocs produce shear stress for fouling control of UF-NF. Superior quality of permeate is achieved with the combined coagulation-UF-NF process.

Investigation of the fouling behaviors correlating to water characteristics during the ultrafiltration with ozone treatment.

This study investigated the fouling behavior and mechanism of ozone treatment correlating to water characteristics for micro-polluted water during ultrafiltration (UF). The results indicated that pre-ozonation efficiently mitigated membrane fouling of natural organic matter (NOM). The higher ozone doses were, the more the performance transmembrane pressures (TMPs) decreased. Ozone mainly converted macro molecule organics into low molecule organics. Macro molecular biopolymers (BP) can be removed up to 35.5% with an ozone treatment of 9 mg/L, while low molecular weight building blocks of acids and humics (BB) and neutrals (LMWN) increased 7.25% and 14.62%, respectively, with an ozone treatment of 9 mg/L. Analysis of fluorescence excitation emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) indicated that ozone mainly removed soluble microbial organics and fulvic-like and humic-like organics but not tyrosine organics. Hydrophobic organics (HPO) were reduced with an increase of ozone doses, especially macro molecular BP and humic substances (HS), and the neutral hydrophilic fraction (N-HPI) was enhanced. Ozone treatment helped to reduce the interception of BP and HS in HPO and improved the interception of BP and HS in N-HPI, as well as BB and LMWN, in both fractions. Principal component analysis suggested that BP, as well as UV254, had high correlations with a membrane fouling index, which can be used as the fouling indicator during ozone treatment.

Degradation of carbamazepine by vacuum-UV oxidation process: Kinetics modeling and energy efficiency.

Vaccum-ultraviolet (VUV) is effective for elimination of organic contaminants in aqueous environment and degradation of carbamazepine (CBZ) by VUV irradiation was systematically investigated in this study. A dynamic kinetic model was developed to simulate the destruction of CBZ that is mainly initiated by hydroxyl radicals (HO). The second-order rate constant of the reaction between CBZ and HO was determined to be 1.4 × 109 M-1 s-1. Effect of initial CBZ concentration, VUV irradiation intensity and natural organic matter (NOM) were further investigated in several batch experiments. The predicted CBZ removal rates increased with the increasing VUV intensity, while decreased with the increasing initial CBZ and NOM concentrations. Based on the electrical energy per order (EE/O) calculation, the optimal VUV intensity was determined to be 7.5 × 10-8 Einstein s-1. Meanwhile, several intermediates/products were identified and their time-dependent evolution profiles were determined, and finally a plausible degradation pathway of CBZ was proposed. Ecotoxicity assessment indicated that the potential toxicity of CBZ and its oxidation products should be paid more attention in the VUV process.

Analysis of organic foulants in the coagulation-microfiltration process for the treatment of Taihu Lake.

This paper analysed organic foulants in the coagulation-microfiltration process for Taihu Lake treatment. High-performance size-exclusion chromatography (HPSEC) and fluorescence excitation-emission matrices (EEM) were applied to elucidate the influence of characteristics of organics on microfiltration (MF) membrane fouling. Results showed that coagulation pretreatment could extend the operation duration of MF based on the fact that pretreatment could effectively remove macromolecular substances as well as a portion of small molecular weight (MW) organics. The analysis of foulants indicated that organics of strong hydrophobic acids (SHA) and neutral hydrophilic (Neut) fractions (based on hydrophobicity) and medium and small MW components (based on MW distribution) contributed greatly to irreversible fouling. EEM fluorescence analysis of chemical solutions exhibited that aromatic proteins and soluble microbial products were mainly a response to irreversible fouling.

Fate and UF fouling behavior of algal extracellular and intracellular organic matter under the influence of copper ions.

Copper ion plays an important role in the outbreak of algal blooms. The aim of this research was to investigate the fate and fouling behavior of algal extracellular organic matter (EOM) and intracellular organic matter (IOM) under different copper concentrations during ultrafiltration (UF). Under the lowest copper concentration of 0.01 µmol/L, both the EOM and IOM caused the largest decrease in filtration flux, followed by EOM under high copper concentrations of 0.3 µmol/L and 0.1 µmol/L; less membrane fouling was induced by IOM under a copper concentration of 0.3 µmol/L than under a copper concentration of 0.1 µmol/L. More reversible fouling (Rre) was induced by EOM/IOM at the lowest copper concentration of 0.01 µmol/L than under the other two copper concentrations, whereas more membrane fouling was induced by EOM than by IOM under the different copper concentrations. Fluorescence excitation-emission matrices-parallel factor analysis (PARAFAC) indicated that fouling by the protein-like components in EOM was more irreversible under 0.01 µmol/L copper than under 0.1 µmol/L and 0.3 µmol/L copper. However, the fouling by this component was more reversible in the IOM solutions than in the EOM solutions. The amount of macromolecular biopolymers was highly correlated with the total and reversible membrane fouling during the EOM/IOM filtration, whereas a weaker correlation (r2) between the humic-like organics and membrane fouling was determined by Pearson's correlation matrix analysis. High-performance size exclusion chromatography (HPSEC) combined with peak-fitting prediction was suggested to be more suitable for membrane fouling implication in algal water treatment.

[Effects and Mechanism of the Combination of Ozone-PAC as a Pretreatment for the Reduction of Membrane Fouling].

The effects of ozone, powdered activated carbon (PAC), and their combination on controlling fouling and the removal of organic matter were investigated. The results showed that ozone mainly oxidized strong hydrophobic, high relative molecular mass (Mr) compounds and the high Mr was transferred to medium and small Mr hydrophilic fractions. Ozone could control fouling effectively, demonstrating that hydrophobic organic matter with higher Mr contributed to membrane fouling. PAC adsorbed organics with small Mr and alleviated membrane fouling, showing that organics with small Mr contributed also to membrane fouling. The ozone and PAC combination controlled membrane fouling and also enhanced the removal of organics, demonstrating the synergistic effect of such a combination.

Investigation of the mechanisms of membrane fouling by intracellular organic matter under different iron treatments during ultrafiltration.

Iron is an important trace element in algal growth and water eutrophication. This study focused on the ultrafiltration (UF) membrane fouling mechanism by the intracellular organic matter (IOM) of Microcystis aeruginosa under different iron treatments. The results indicated that the membranes experienced faster flux decline and worse fouling reversibility when the IOM formed under low iron concentrations. In contrast, less IOM membrane fouling was found under normal and high iron concentrations. The mass balances of the dissolved organic carbon (DOC) content implied that the IOM in the low-iron treatment was associated with higher IOM retention and a higher capacity of reversibly deposited organics, whereas more IOM in the high-iron treatment passed through the UF membrane. The IOM in the low-iron treatment was composed of more biopolymer macromolecules, whereas the IOM in the high-iron treatment contained more UV-absorbing hydrophobic organics. The fluorescence excitation-emission matrix (EEM) spectra coupled with peak-fitting analysis implied that the fouling associated with protein-like components was more irreversible in the low-iron treatment than those in the normal- and high-iron treatments. Cake formation combined with intermediate blocking was identified as the main membrane fouling mechanism responsible for the flux decline caused by IOM solutions in the three iron treatments in this study.