Impact of coagulation and adsorption on DOC fractions of secondary effluent and resulting fouling behaviour in ultrafiltration

Membrane fouling by macromolecular dissolved organic compounds is still a fundamental drawback in low-pressure membrane filtration of secondary effluent. In this study, pre-treatment of secondary effluent by coagulation and/or adsorption was investigated in terms of removal of different dissolved organic carbon (DOC) fractions, especially macromolecular substances. DOC fractionation has been characterised by size exclusion chromatography. Adsorption tests using four commercially available activated carbons yielded a removal of small as well as larger organic compounds, revealing differences in the affinity towards macromolecules depending on the type of applied activated carbon. By contrast, coagulation removed predominantly larger molecules, i.e., biopolymers and humic substances. In terms of DOC reduction, the coagulant ferric chloride was superior to aluminium chloride. A combination of coagulation and adsorption resulted in the addition of individual removal efficiencies, suggesting that different fractions of organic compounds were involved in each of the processes. After removal of macromolecular organic compounds either by coagulation or by adsorption, a significant reduction of membrane fouling was observed in tests using two different types of ultrafiltration flat-sheet membranes in 20-h cross-flow filtration tests.     

混凝/砂滤结合GAC/UF法处理洗车废水的研究

采用混凝、沉淀-砂滤-GAC-UF工艺对洗车废水进行回用处理,结果表明该工艺的处理效果良好,出水水质可满足洗车水回用的水质要求。混凝、沉淀、砂滤预处理工艺对浊度、LAS和氨氮的去除效果较好,可大大减轻后续深度处理工艺的负荷,延缓GAC／UF反应器的堵塞进程;GAC单元对LAS的去除率〉70％,是整个系统去除LAS的主要单元;UF单元对浊度的去除率〉90％,是出水浊度的有效控制单元。采用该工艺处理洗车废水并回用,每年可节省费用约1．2万元,经济效益显著。     

Effects of super-powdered activated carbon pretreatment on coagulation and trans-membrane pressure buildup during microfiltration

As a pretreatment for membrane microfiltration (MF), the use of powdered activated carbon (PAC) with a particle size much smaller than that of conventional PAC (super-powdered PAC, or S-PAC) has been proposed to enhance the removal of dissolved substances. In this paper, another advantage of S-PAC as a pretreatment for MF is described: the use of S-PAC attenuates trans-membrane pressure increases during the filtration operation. The floc particles that formed during coagulation preceded by S-PAC pretreatment were larger and more porous than the floc particles formed during coagulation preceded by PAC pretreatment and those formed during coagulation without pretreatment. This result was due to increased particle–particle collision frequency and better removal of natural organic matter, which inhibits coagulation by consuming coagulant, before the coagulation reaction. The caked fouling layer that built up on the membrane surface was thus more permeable with S-PAC than with normal PAC. Both physically reversible and irreversible membrane foulings were reduced, and more stable filtration was accomplished with S-PAC pretreatment.     

微污染北江源水的深度处理工艺优选

采用预氧化＋常规处理＋深度处理工艺对微污染北江源水进行了中试研究，考察了在预臭氧、预氯化和无预处理方式下，GAC和O3-BAC深度处理工艺的除污效果。结果表明：采用预臭氧氧化方式可大大改善常规处理工艺对CODMn、UV254的去除效果；在预臭氧氧化方式下，O3-BAC和GAC深度处理工艺均能在长时间内保持对有机物的高效去除，且前者的去除效果及其活性炭的使用周期均优于后者；活性炭吸附对氨氮无明显去除效果，而生物降解能较好地去除氨氮；预臭氧氧化能有效去除原水中的THMFP，但生成的CHCl3不能通过生物降解被去除，只能被活性炭所吸附，在活性炭吸附饱和后出水CHCl3浓度比进水的高；从长远角度考虑，对于北江源水，预臭氧＋常规处理＋O3-BAC是一种较优的组合工艺，它能够有效去除饮用水中的有毒、有害物质，并保障饮用水的安全性。     

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks).Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM.     

Removal of micropollutants from aerobically treated grey water via ozone and activated carbon

Ozonation and adsorption onto activated carbon were tested for the removal micropollutants of personal care products from aerobically treated grey water. MilliQ water spiked with micropollutants (100-1600 μgL⁻¹) was ozonated at a dosing rate of 1.22. In 45 min, this effectively removed (>99%): Four parabens, bisphenol-A, hexylcinnamic aldehyde, 4-methylbenzylidene-camphor (4MBC), benzophenone-3 (BP3), triclosan, galaxolide and ethylhexyl methoxycinnamate. After 60 min, the removal efficiency of benzalkonium chloride was 98%, tonalide and nonylphenol 95%, octocrylene 92% and 2-phenyl-5-benzimidazolesulfonic acid (PBSA) 84%. Ozonation of aerobically treated grey water at an applied ozone dose of 15 mgL⁻¹, reduced the concentrations of octocrylene, nonylphenol, triclosan, galaxolide, tonalide and 4-methylbenzylidene-camphor to below limits of quantification, with removal efficiencies of at least 79%. Complete adsorption of all studied micropollutants onto powdered activated carbon (PAC) was observed in batch tests with milliQ water spiked with 100-1600 μgL⁻¹ at a PAC dose of 1.25 gL⁻¹ and a contact time of 5 min. Three granular activated carbon (GAC) column experiments were operated to treat aerobically treated grey water. The operation of a GAC column with aerobically treated grey water spiked with micropollutants in the range of 0.1-10 μgL⁻¹ at a flow of 0.5 bed volumes (BV)h⁻¹ showed micropollutant removal efficiencies higher than 72%. During the operation time of 1728 BV, no breakthrough of TOC or micropollutants was observed. Removal of micropollutants from aerobically treated grey water was tested in a GAC column at a flow of 2 BVh⁻¹. Bisphenol-A, triclosan, tonalide, BP3, galaxolide, nonylphenol and PBSA were effectively removed even after a stable TOC breakthrough of 65% had been reached. After spiking the aerobically treated effluent with micropollutants to concentrations of 10-100 μgL⁻¹, efficient removal to below limits of quantification continued for at least 1440 BV. Both ozonation and adsorption are suitable techniques for the removal of micropollutants from aerobically treated grey water.     

粉末活性炭/污泥回流工艺强化膜前预处理的研究

采用粉末活性炭(PAC)吸附/混凝沉淀/浸没式超滤膜组合工艺处理苏州市某河水,考察了PAC/污泥回流工艺对膜前预处理的强化效果及对膜污染的影响,并与常规混凝沉淀、污泥回流强化混凝沉淀、PAC吸附/混凝沉淀等3种预处理工艺进行了对比。结果表明,PAC/污泥回流强化预处理工艺对浊度、DOC、UV254和THMFP的去除率分别为80.2%、47.5%、42.3%和52.3%,均比其他预处理工艺的高,对MW30 ku和MW1 ku有机物的去除效果明显。PAC/污泥回流强化预处理和超滤膜组合工艺对浊度、DOC、UV254和THMFP的去除率分别可达到99.2%、54.1%、47.2%和60.2%;经过15 d的运行,超滤膜的跨膜压差基本保持稳定,而其他预处理工艺虽能在一定程度上减轻膜污染,但无法避免不可逆膜污染的发生。     

Rapid and direct estimation of active biomass on granular activated carbon through adenosine tri-phosphate (ATP) determination

Granular activated carbon (GAC) filtration is used during drinking water treatment for the removal of micropollutants such as taste and odour compounds, halogenated hydrocarbons, pesticides and pharmaceuticals. In addition, the active microbial biomass established on GAC is responsible for the removal of biodegradable dissolved organic carbon compounds present in water or formed during oxidation (e.g., ozonation and chlorination) processes. In order to conduct correct kinetic evaluations of DOC removal during drinking water treatment, and to assess the state and performance of full-scale GAC filter installations, an accurate and sensitive method for active biomass determination on GAC is required. We have developed a straight-forward method based on direct measurement of the total adenosine tri-phosphate (ATP) content of a GAC sample and other support media. In this method, we have combined flow-cytometric absolute cell counting and ATP analysis to derive case-specific ATP/cell conversion values. In this study, we present the detailed standardisation of the ATP method. An uncertainty assessment has shown that heterogeneous colonisation of the GAC particles makes the largest contribution to the combined standard uncertainty of the method. The method was applied for the investigation of biofilm formation during the start-up period of a GAC pilot-scale plant treating Lake Zurich water. A rapid increase in the biomass of up to 1.1 x 10(10)cells/g GAC dry weight (DW) within the first 33 days was observed, followed by a slight decrease to an average steady-state concentration of 7.9 x 10(9)cells/g GAC DW. It was shown that the method can be used to determine the biomass attached to the GAC for both stable and developing biofilms.     

含炭高密度沉淀池/超滤工艺处理污水厂二级出水

采用含炭高密度沉淀池/超滤组合工艺处理污水厂二级出水,考察了其对常规指标和微量有机污染物的去除效能,并对膜污染特性进行了分析。结果表明,组合工艺对浊度的去除率高达99.9%,出水浊度在0.01 NTU左右;对DOC、UV(254)、TP、氨氮和TN的平均去除率分别为41.02%、49.82%、60.44%、23.34%和10.90%;三维荧光光谱分析表明,组合工艺能有效去除水中的腐殖质和蛋白质类有机物;通过LC-MS/MS检测水中微量有机污染物发现,组合工艺可以使水中的微量有机污染物含量下降66%以上;同时含炭高密度沉淀池预处理能有效减轻膜污染,使跨膜压差增长速度减缓。     

活性炭吸附用于城市污水地下回灌技术的研究

通过静态吸附试验比较与Ｃｒｉｔｔｅｎｄｅｎ计算模型分析,选择ＧＨ－１６型粒状活性炭对北京高碑店污水处理厂二级出水进行深度处理试验。结果表明：ＧＨ－１６型活性炭的净化效果存在阈值,约２５％的ＤＯＣ不能被吸附,不被吸附的主要是分子量〉３０００ｕ的有机物。对以ＵＶ２５４表征的有机物去除效果最好,分子量〈１０００ｕ的弱极性有机物易被微孔吸附且吸附容量,对以ＡＯＸ表征的极性有机物去除效果较差。二级出水经活性     

Removal of micropollutants and reduction of biological activity in a full scale reclamation plant using ozonation and activated carbon filtration

Pharmaceutical compounds are found in secondary treated effluents up to μg L^-1 levels and therefore discharged into surface waters. Since the long term effects of these compounds on the environment and human health are, to date, largely unknown, implementation of advanced treatment of wastewaters is envisaged to reduce their discharge. This is of particular relevance where surface waters are used as drinking water sources and when considering indirect potable reuse. This study aimed at assessing the removal of organic micropollutants and the concurrent reduction of their biological activity in a full scale reclamation plant treating secondary effluent. The treatment consists of 6 stages: denitrification, pre-ozonation, coagulation/flocculation/dissolved air flotation and filtration (DAFF), main ozonation, activated carbon filtration and final ozonation for disinfection. For that purpose, representative 24-hour composite samples were collected after each stage. The occurrence of 85 compounds was monitored by LC/MS-MS. A battery of 6 bioassays was also used as a complementary tool to evaluate non-specific toxicity and 5 specific toxic modes of action. Results show that, among the 54 micropollutants quantified in the influent water, 50 were removed to below their limit of quantification representing more than 90% of concentration reduction. Biological activity was reduced, depending on the specific response that was assessed, from a minimum of 62% (AhR response) to more than 99% (estrogenicity). The key processes responsible for the plant's performances were the coagulation/flocculation/DAFF, main ozonation and activated carbon filtration. The effect of these 3 processes varied from one compound or bioassay to another but their combination was almost totally responsible for the overall observed reduction. Bioassays yielded complementary information, e.g. estrogenic compounds were not detected in the secondary effluent by chemical analysis, but the samples had an estrogenic effect. The main ozonation formed oxidation by-products of the organic micropollutants but decreased the level of non-specific toxicity and other specific toxic modes of action, demonstrating that the mixture of oxidation by-products was less potent than the mixture of the parent compounds for the considered effects.     

Membrane filtration of two sulphonamides in tertiary effluents and subsequent adsorption on activated carbon

The adsorption behaviour of two polar organic micropollutants (N-n-butylbenzenesulphonamide and sulphmethoxazole) onto powdered activated carbon (PAC) under competitive conditions prior to and after filtration with a tight ultrafiltration membrane was examined. The sulphonamides were spiked into microfiltered tertiary municipal effluent in microg L(-1) quantities. Ultrafiltration of these effluents resulted in better adsorbability for both the micropollutants and the background organic matter in the permeates compared to the feed waters. This behaviour seems to be caused by a reduced blocking of micropores by lower concentrations of high molecular weight compounds in membrane filtrates. A combined treatment of ultrafiltration prior to adsorption can therefore reduce the carbon demand for potentially harmful micropollutants in effluents.     

Drinking water treatment options for taste and odor control

The effectiveness of drinking water treatment options for eliminating seasonal taste and odor events caused by phytoplankton blooms in the source water were evaluated. Dissolved air flotation (DAF), conventional gravity sedimentation (CGS), ozonation and granulated activated carbon (GAC) filtration processes were studied in pilot plant-scale experiments. Clarification by DAF consistently produced water with lower turbidity and particle counts (NP > 2.0 μm/ml) than CGS. Mean particle counts detected in water following DAF and CGS treatment were 3600 and 7500 particles/ml, respectively. The absolute abundance of phytoplankton in the source water was the single most important factor influencing DAF and CGS removal efficiency. Removal efficiencies for both processes were poorer at low source water biomass (near 250 μg/l) than at higher biomass concentrations (1750 μg/l). For the eight phytoplankton taxa present in the source water, DAF and CGS removal ranged from 29–85% and 21–49%, respectively. With the exception of the total nanoplankton for which removal by both processes was comparable, all other taxa were removed more efficiently by DAF than CGS. Flavor profile analysis (FPA) indicated that DAF alone could not completely mitigate the strong fishy, musty odors associated with some phytoplankton blooms. Ozone altered the fishy odor to an undesirable “plastic-like” odor. Only filtration through GAC/sand filters removed all odors. Removal of soluble constituents such as color and total organic carbon (TOC) by DAF and CGS were comparable for most of the year. During phytoplankton blooms, however, TOC removal by DAF was significantly greater than by CGS. TOC and color removal were substantially greater through GAC than through anthracite filters. A combination of DAF clarification and GAC filtration was the most effective treatment combination for removal of particulates, color and taste and odor compounds.     

Comparaison de l'elimination de molecules organiques par coagulation-floculation et par adsorption sur flocs d'hydroxyde metallique preformesComparison of organic compounds removal by coagulation-flocculation and by adsorption onto preformed hydroxide flocs

The coagulation process is traditionally described in terms of the destabilization of colloids present in a water supply. Many studies show that coagulants are not only used to destabilize organic or inorganic colloidal particles, but also to remove natural organic matter. The removal of this organic matter from the bulk water can occur by direct precipitation or by adsorption of the organic matter onto metal hydroxides. The goal of this study is to compare the removal of organic compounds by coagulation and by adsorption onto preformed flocs with aluminium and iron salts who are the most used coagulants in drinking water treatment.

Various studies (Chadick and Amy, 1987; Dentel and Gosset, 1988; Edwards and Amirtharajah, 1985; Hundt and O'Melia, 1988; Jekel, 1986; Randtke, 1988; Tipping et al., 1988) have been reported concerning the removal of humic substances and the removal of low molecular weight compounds (Lefebvre, 1990; Lefebvre et al., 1990).

Only a few studies show the interactions between preformed hydroxide flocs surface and these organic compounds.     

臭氧/活性炭工艺深度处理微污染水源水的中试

以邯郸市滏阳河水为原水,进行臭氧/活性炭工艺深度处理微污染水源水的中试研究.中试采用混凝沉淀/Zeo-carbon生物滤池/臭氧/活性炭工艺,综合考察臭氧/活性炭对浊度、COD<,Mn、UV<,254>、NH<,4><'+>-N等指标的去除效果.结果表明,在该深度处理工艺中,臭氧的最佳投加量为2.0 mg/L,活性炭滤池的最佳滤速为6.0 m/h.在最佳运行工况下,出水浊度、COD、NH<,4><'+>-N、UV<,254>的平均值分别为0.85 NTU、2.43 mg/L、0.33 mg/L和0.031 cm<'-1>,平均去除率分别为62.4%、53.5%、73.0%和59.4%,出水水质满足<生活饮用水卫生标准>(GB 5749-2006)的要求.     

Comparaison de l'elimination de molecules organiques par coagulation-floculation et par adsorption sur flocs d'hydroxyde metallique preformes

The coagulation process is traditionally described in terms of the destabilization of colloids present in a water supply. Many studies show that coagulants are not only used to destabilize organic or inorganic colloidal particles, but also to remove natural organic matter. The removal of this organic matter from the bulk water can occur by direct precipitation or by adsorption of the organic matter onto metal hydroxides. The goal of this study is to compare the removal of organic compounds by coagulation and by adsorption onto preformed flocs with aluminium and iron salts who are the most used coagulants in drinking water treatment.Various studies (Chadick and Amy, 1987; Dentel and Gosset, 1988; Edwards and Amirtharajah, 1985; Hundt and O'Melia, 1988; Jekel, 1986; Randtke, 1988; Tipping et al., 1988) have been reported concerning the removal of humic substances and the removal of low molecular weight compounds (Lefebvre, 1990; Lefebvre et al., 1990).Only a few studies show the interactions between preformed hydroxide flocs surface and these organic compounds.     

Coagulation of humic substances and dissolved organic matter with a ferric salt: an electron energy loss spectroscopy investigation

Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) was used to investigate the coagulation of natural organic matter with a ferric salt. Jar-test experiments were first conducted with a reconstituted water containing either synthetic or natural extracts of humic substances, and then with a raw water from Moselle River (France). The characterization of the freeze-dried coagulated sediment by EELS in the 250-450 eV range, showed that Fe-coagulant species predominantly associate with the carboxylic groups of organic matter, and that this interaction is accompanied by a release of previously complexed calcium ions. The variation of Fe/C elemental ratio with iron concentration provides insightful information into the coagulation mechanism of humic substances. At acid pH, Fe/C remains close to 3 over the whole range of iron concentrations investigated, while a much lower atomic ratio is expected from the value of optimal coagulant dosage. This suggests that a charge neutralization/complexation mechanism is responsible for the removal of humic colloids, the aggregates being formed with both iron-coagulated and proton-neutralized organic compounds. At pH 8, the decrease in Fe/C around optimal coagulant concentration is interpreted as a bridging of stretched humic macromolecules by Fe-hydrolyzed species. Aggregation would then result from a competition between reconformation of humic chains around coagulant species and collision of destabilized humic material. EELS also enabled a fingerpriting of natural organic substances contained in the iron-coagulated surface water, N/C elemental analyses revealing that humic colloids are removed prior to proteinic compounds.     

Characterization and treatability of aerobic bacterial thermophilically treated wastewater by a conventional activated sludge and granular activated carbon

An industrial wastewater that was pretreated by an aerobic thermophilic bacterial consortium (THE) was subjected to additional treatability studies by granular activated carbon (GAC) and a conventional activated sludge (CAS). The removal of dissolved organic carbon (DOC) in both systems was generally found to be similar. While GAC was able to attain better effluent concentrations of toluene and methyl isobutyl ketone (MIBK), the CAS was much more efficient at removing acetone. Furthermore, unlike the GAC, the performance of the CAS was not influenced by the high degree of variability in the influent wastewater. Characterization of the influent thermophilic wastewater using gas chromatography-mass spectroscopy (GC/MS) was performed to quantify the micropollutants as well as to evaluate removal efficiencies from the GAC and CAS systems.     

混凝和活性炭联用对有机物质的去除效果

研究了混凝和粉末活性炭对水中腐殖酸和苯酚的去除效果,选用聚合氯化铝作为混凝剂和粉末活性炭分别和联合使用时对水中腐殖酸和苯酚的去除效果进行了考察,结果表明：单独使用聚合氯化铝对苯酚的去除效果不佳,先投加活性炭后投加聚合氯化铝比两种同时投加时效果更好。     

Bromate ion removal by activated carbon

Bromate ion removal by powdered activated carbon (PAC) in batch mode and granular activated carbon (GAC) in continuous mode was evaluated under various operational conditions. For PAC, removal kinetics were found to be prohibitively slow, with high PAC doses required; removal improved with decreasing pH and decreasing natural organic matter. GAC was also influenced by these same water quality conditions, with an additional influence by empty bed contact time (EBCT). Bromate ion was found to be reduced to bromide ion and not all bromide in bromate was recovered supporting the theory that bromate reduction involves non-equilibrium sorption-reduction mechanisms. Both PAC and GAC results were found to be carbon-specific.