[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.

[Influencing Factors of Assimilable Organic Carbon (AOC) Formation in Drinking Water During Ozonation Process].

The influences of ozone dosage, pH and ionic strength on the formation of Assimilable Organic Carbon (AOC) during ozonation were investigated. The result demonstrated that within the range of 1-5 mg · L⁻¹ O3, the formation of AOC increased with increasing ozone dosage, but higher ozone dosage (9 mg · L⁻¹) resulted in reduction of AOC formation. AOC formation increased with higher pH but decreased with increasing ionic strength. The result also showed that AOC formation with hydrophobic fraction (HPO) was the most, followed by transphilic fraction (TPI), and charged hydrophilic fraction (CHPI), while neutral hydrophilic fraction (NHPI) was the least. It was found that AOC formation related closely with SUVA of small molecular weight organics, and the lower SUVA produced more AOC.

[Effects and mechanism on removing organics and reduction of membrane fouling using granular macro-porous anion exchange resin in drinking water treatment].

A granular macro-porous anion exchange resin combined with coagulation was used as pretreatment of microfiltration membrane, and their effects and mechanism on removing organics and reduction of membrane fouling were evaluated. The results showed that resin could be effective in removing organics with medium and small molecular weight ( Mr) but ineffective in removing organics with large Mr, while couagulation could significantly remove organics with large Mr, with a limited removal for organics with medium and small Mr. Using resin alone as pretreatment could be effective in removal of organics but limited in reduction of membrane fouling. With combination of coagulation and resin as pretreatment of microfiltration, not only organics could be removed effectively, but also membrane fouling could be reduced.

[Effect of relative molecular mass distribution and hydrophilicity/ hydrophobicity of NOM on membrane fouling in MF-combined process].

This study investigated the reversible and irreversible foulants in a submerged microfiltration (MF) with pretreatments (coagulation/powdered activated carbon (PAC)/potassium permanganate) in a pilot scale treatment of water from Taihu Lake. The study focused on the effect of relative molecular mass (M(r)) distribution and hydrophilicity/hydrophobicity on membrane fouling using high performance size-exclusion chromatography (HPSEC) with UV and TOC detectors and three dimension fluorescence excitation-emission matrix (3DEEM). HPSEC analyses showed that pretreatments could almost completely remove the macro molecules (M(r) > 10 x 10(3)), but only eliminate part of medium (10 x 10(3)) > M(r) > 1 x 10(3)) and micro molecules (M(r) < 1 x 10(3)). A majority of medium and micro molecules were found in chemical cleaning solutions, indicating that medium and micro molecules were the main foulants that contributed to irreversible membrane fouling. In addition, it was also found that the content of strong hydrophobic acids (SHA) and neutral hydrophilic (Neut) fractions in chemical solutions were far higher than that of weakly hydrophobic acids (WHA) and charged hydrophilic (Char), which suggested that both organic fractions were responsible for irreversible fouling. 3DEEM fluorescence demonstrated that aromatic proteins and soluble microbial products were the main contributors to irreversible membrane fouling.

[DOM membrane fouling and effects on rejection behaviors of NF membranes].

This work investigated membrane fouling caused by two kinds of dissolved organic matters (DOMs), i. e., Qingcaosha (QCS) DOM and Taihu lake (TH) DOM, and the effects on the rejection behaviors of two different nanofiltration (NF) membranes, i. e., HL and ESNA1-K, using carbamazepine (CBZ) as a molecular indicator. The results showed that severe membrane fouling occurred in the presence of DOM. And the CBZ removal rate was associated with the properties and characteristics of the organic matters and the membranes. It was found that the hydrophobicity of adhered DOM cake layer was responsible for the flux decline and the influence of CBZ removal. QCS DOM increased the retention of CBZ, while TH DOM decreased the rejection rate of CBZ by both membranes tested. DOMs at medium relative molecular weight (M(r) 1 500-10 000) could adhere closely to NF membranes to form cake layer, thus changed the hydrophobicity of the membranes. DOMs at low molecular weight could enter the membrane pores reducing the M(r), which influenced the CBZ removal and resulted in membrane fouling. The experiment also showed that DOM of TH contained more hydrophobic organic matters than that of QCS, the adhesion free energy and cohesion free energy of which was more negative, and the resulting membrane fouling and membrane flux decline were more severe.

[Determination of the distribution of relative molecular mass of organic matter by high pressure size exclusion chromatography with UV and TOC detectors].

An on-line high pressure size exclusion chromatography (HPSEC) with UV and TOC detectors was adapted to examine the distribution of relative molecular mass of natural organic matter (NOM). Through synchronous determination of UV254 and TOC responses in a wide range of relative molecular mass, it was possible to accurately characterize the structure of NOM, especially for some non-aromatic and non-conjugated double bond organics which have low response to UV. It was found that, TOC detector was capable of detecting all kinds of organic matters, including sucrose, sodium alginate and other hydrophilic organic compounds. The sample volume had a positively linear correlation with the TOC response, indicating that the larger volume would produce stronger responses. The effect of ion strength was relatively low, shown by the small decrease of peak area (1.2% ) from none to 0.2 mol x L(-1) NaCl. The pH value of tested samples should be adjusted to neutral or acidic because when the samples were alkaline, the results might be inaccurate. Compared to the sample solvents adopted as ultrapure water, the samples prepared by mobile phase solvents had less interference to salt boundary peak. The on-line HPSEC-UV-TOC can be used accurately to characterize the distribution of relative molecular mass and its four fractions in River Xiang.

[Researches on factors affecting the removal of carbamazepine by nanofiltration membranes].

The influence factors on removal of carbamazepine (CBZ) in drinking water by nanofiltration membrane was mainly investigated. The effect of CBZ removal by NF270 and NF90 was firstly compared and found that removal efficiency by NF90 with small pore size showed more effectively than removed by NF270 with large pore size. The next experiment focused on the effect of various factors on removal with respect to CBZ initial concentration, pH, ionic strength and water temperature. The results showed that removal efficiency reduced with decreased pH and increased Ca2+ concentration and water temperature. The effect of initial concentration in the range of 50-500 microg/L on flux and CBZ removal was insignificant. It can be concluded that the retention of non-ionic CBZ by loose NF membrane was strongly dependent on the mechanism of steric (size) exclusion.

[Effect of ozone/coagulation pretreatment on membrane fouling reduction].

In order to investigate the effect of ozone and coagulation pretreatments on organic matter and MF membrane filtration, pretreated Huangpu River surface water was filtrated by MF membrane. The results showed that there were the optimal dosages of ozone and coagulant made maximum membrane flux. The result of membrane fouling reduction by coagulation was better than that by ozone, which was relative to character of organic matter removed by two pretreatment processes. Organics in Huangpu River water mostly concentrates in relative molecule mass (Mr) ranging 3 x 10(3)-5 x 10(3). Research on the chemical cleaning of the fouled membrane indicated that fouling organic substance concentrated about Mr 4.5 x 10(3). Removals of Mr 3 x 10(3) organic matter are higher than Mr 5 x 10(3) organic matter by ozone oxidation. Coagulation process can remove 5 x 10(3) high relative molecular mass organic matter effectively. Removal of these organics fouled membrane by coagulation was better than that by ozone, thereby to effectively reduce membrane fouling.

[Characteristic of algogenic organic matter (AOM) membrane fouling and its effect on UF membrane fouling].

Algogenic organic matter (AOM) was extracted from blue-green algae (Cyanobacteria) and its characteristics was determined by various methods including high-pressure size-exclusion chromatography (HP-SEC), hydrophobic and hydrophilic fractionation and fluorescence excitation emission matrix (EEM). The results showed that AOM was composed of hydrophilic fraction predominantly, account for 78%. The SUVA of AOM was only 1.1 L/(mg x m). The analysis for relative molecular weight (Mr) demonstrated that organic matter greater than 30,000 accounted for above 40% and mostly was composed of neutral hydrophilic compound. EEM analyses revealed that protein-like and humic substances existed in AOM. A test for membrane filtration exhibited that AOM could make ultrafiltration membrane substantial flux decline, which can be attributed to membrane pore clog caused by neutral hydrophilic compound with larger MW.

Formation of chloroform during chlorination of alanine in drinking water.

Currently, dissolved nitrogenous organic matters in water, important precursors of disinfection by-products (DBPs), are of significant concern. This study was to explore the formation of chloroform (CF) during chlorination of alanine (Ala), an important nitrogenous organic compound commonly present in water sources. Our results indicated that the CF yield reached a maximum value of 0.143% at the molar ratio of chlorine atom to nitrogen atom (Cl/N)=1.0 over a Cl/N range of 0.2-5.0 (pH=7.0, reaction time=5d, and initial Ala=0.1mM). At an acidic-neutral condition (pH 4-7), the formation of CF was suppressed. However, the highest CF yield (0.227%) occurred at weakly alkaline condition (pH 8.0) (initial Ala=0.1mM, and Cl/N=1.0). The increase of Br(-) in water can increase total trihalomethanes (THMs) and bromo-THMs. However, the bromo-THMs level reached a plateau at Br(-)/Cl>0.04. Finally, based on the computation of frontier electron density and identification and measurement of key intermediates during Ala chlorination, we proposed a formation pathway of CF from Ala chlorination: Ala-->monochloro-N-alanine (MC-N-Ala)-->acetaldehyde (AAld)-->monochloroacetaldehyde acetaldehyde (MCAld)-->dichloroacetaldehyde (DCAld)-->trichloroacetaldehyde (TCAld)-->CF.

[Effect of preozonation on microfiltration for Huangpu River].

This study investigated the effect of preozonation on organic matter and microfiltration membrane filtration, Huangpu River surface water ozonated was filtrated by MF membrane. The results show that highest rejection efficiency of DOC and UVr by ozone are 10% and 71% respectively during 0.5-3.0 mg/L ozone dosage. With increasing of ozone concentration, organic substances of 2 x 10(3)-7 x 10(3) reduce gradually, while organic matter of which less than 0.5 x 10(3) change slightly. Ozone oxidizes more hydrophobic fraction to hydrophilic one and only few to inorganic matter. Changes of organic matter composition affect membrane filtration resistance, thereby improve membrane flux. There is the optimal dosage with ozone of 1.5 mg/L made membrane flux maximum in the range of 0.5-3.0 mg/L ozone dosage. The reason is change of organic matter composition which made membrane filtration resistance minimum in the ozone dosage of 1.5 mg/L.

[Effect of different organic fraction on membrane flux declines].

Organic matter in the tap water was isolated into strongly hydrophobic acids, weakly hydrophobic acids, charged hydrophilic and neutral hydrophilic by DAX-8, XAD-4 and IRA-958 synthetic resins. Filtration tests using polyvinylidene fluoride (PVDF), polyethersulphone (PES) and cellulose acetate (CA) membranes were conducted to investigate the contribution of different organic fractions to membrane fouling. The results show that in filtration of raw water, flux declines with PES, PVDF and CA membrane are 67%, 59% and 19% of the initial flux, indicating that the more hydrophobic membrane resulted in more severe fouling. For the effect of different fractions on flux, flux decline with neutral hydrophilic is 41%-75% of the initial flux, whereas weakly hydrophobic acids is 6%-33%, suggesting that neutral hydrophilic has a great impact on filtration flux. Among three membranes tested, CA membrane shows the lowest flux decline compared with other membranes in spite of rejection of as high as 14.69% of neutral hydrophilic, suggesting that the extent of flux decline may not be associated with the total amount of NOM removed. The mechanism of fouling was discussed and found that the neutral hydrophilic fraction with greater than 3 x 10(4) of molecular weight caused a significant flux decline, through blocking the pore for the MF or UF having greater relative molecular mass cut-off (MWCO), but resulted in a little impact on flux with the UF having lower MWCO, through forming cake layer on the surface of membrane due to not entering the inside of pore.

[Degradation of MC-LR by combination of UV/H2O2 process].

The degradation of MC-LR in water by UV/H2O2 process was investigated. The effects of intensity of UV radiation, initial concentration of MC-LR, dosages of H2O2, initial pH value and anions on degradation of MC-LR by UV/H2O2 process were studied. The results show that the removal of MC-LR only by H2O2 is nearly zero, and UV process can degrade MC-LR to a certain extent. However, the degradation efficiency of UV/H2O2 process is much higher than UV and H2O2 process due to the synergetic effect between UV and H2O2. The removal of MC-LR increases with the enhancement of intensity of UV radiation, but decreases gradually with the increase of initial concentration of MC-LR. When the dosages of H2O2 change from 1 mmol/L to 3 mmol/L, the constant of degradation rate rises from 0.0844 to 0.1664. The optimum pH value is 3.13. The added anions have adverse effect on the degradation of MC-LR, especially carbonate and nitrate ions have the biggest influence among the studied anions.

[Influence of coagulation pretreatment on UF membrane flux].

In this study, the effect of coagulation pretreatment on improvement of UF membrane filtration flux was investigated. The experiment using four water samples having different hydrophobic and hydrophilic compound was focused on the effect of coagulation on removing hydrophobic and hydrophilic fraction of organics and resulting enhanced flux. In the filtration of raw water, the organics removal for the four water samples were in the ranges of 12% and 20%, in which hydrophobic fraction accounting for over 50%, suggesting that membrane prefers to remove hydrophobic fraction. In the addition of 25 mg/L coagulant, the organics removals for the four water samples were in the ranges of 12% and 28%. As coagulant dosage increased to 100 mg/L, removals increased to 25% and 38% accordingly, in which hydrophobic fraction accounting for over 50%, suggesting that coagulation prefers to remove hydrophobic fraction. Coagulation pretreatment could enhance flux of all of water samples studied. The analyses for each organic compound show that after coagulation pretreatment membrane reject hydrophilic fraction mainly due to removal of hydrophobic fraction effectively by coagulation. It can be concluded that the flux decline of UF membrane was mainly caused by hydrophobic compound and hydrophilic compound had less effect on flux.

Effect of coagulation pretreatment on the fouling of ultrafiltration membrane.

The purpose of this study is to understand the effect and mechanism of preventing membrane fouling, by coagulation pretreatment, in terms of fractional component and molecular weight of natural organic matter (NOM). A relatively higher molecular weight (MW) of hydrophobic compounds was responsible for a rapid decline in the ultrafiltration flux. Coagulation could effectively remove the hydrophobic organics, resulting in the increase of flux. It was found that a lower MW of neutral hydrophilic compounds, which could remove inadequately by coagulation, was responsible for the slow declining flux. The fluxes in the filtration of coagulated water and supernatant water were compared and the results showed that a lower MW of neutral hydrophilic compounds remained in the supernatant water after coagulation could be rejected by a membrane, resulting in fouling. It was also found that the coagulated flocs could absorb neutral hydrophilic compounds effectively. Therefore, with the coagulated flocs formed on the membrane surface, the flux decline could be improved.

[Effect of chlorine on PAC's ability to adsorb microcystin].

Bottle-point experiments were conducted in Huangpu river raw water to examine the extent to which chlorine influenced the ability of powdered activated carbon (PAC) to adsorb two kinds of microcystins (MC-RR and MC-LR). The result shows that,when adding PAC and chlorine at the same point, chlorine can enhance the removal effect of the combined process (about 20%), which may be because the surface of PAC catalyzes the reaction between mirocystin and chlorine molecule, when adding PAC and chlorine at different points, the strengthening effect disappear [chlorine reduces the ability of PAC to microcystins to some extent (5%-10%)], the effect of chlorine to PAC becomes weak when raise the dosage of PAC. PAC can effectively remove microcystins (the removal effect can reach 55% and 45% for MC-RR and MC-LR respectively at the dosage of 10 mg/L, contact time of 6 hours) when using PAC alone.

[Removal of EDCs(BPA) by ultrafiltration and impact factors].

The removal of bisphenol A (BPA) in drinking water was investigated by ultrafiltration membranes (UF) using dead-end stirred-cell filtration system. The experiment was focused on the effect of various factors on removal efficiency with respect to BPA initial concentration, molecular weight cut offs (MWCOs) of membrane, pH, ionic strength and organic matter. The results showed that UF could remove BPA effectively. UF with 2 000 - 10 000 MWCOs removed BPA by over 92%, with initial concentration of BPA ranging from 100 to 600 microg/L. As pH of solution approached the pK(a) of BPA (9.6 - 11.3), BPA removal efficiency dropped significantly. The effect of ionic strength on BPA removal was negligible. The influence of humic acid in solution on BPA removal was minor. It can be concluded that adsorption may play a significant role in UF process for removing hydrophobic molecular BPA.

[Effect of coagulation on preventing membrane from fouling].

In this experiment, the effects on improve of flux and prevention of membrane from fouling is studied. The results demonstrate that after backwashing, the flux was completely recovered by addition of 4mg/L and l0mg/L(as Al), while the flux was only 40% of initial flux without coagulation pretreatment. It is also observed that whether or not prevention of fouling by coagulation are depended on the characteristics of cake layer formed on membrane surface during membrane filtration. In the presence of filtration of coagulation floc suspension, coagulation can form cake layer on membrane surface, thus prevent membrane from fouling effectively, while in the presence of filtration of supernatant, fouling are occurred due to cake layer comprising small, neutral, hydrophilic compounds, which can not remove by backwash.