The effect of ozonation on natural organic matter removal by alum coagulation

Natural organic matter (NOM) was extracted from a moderately colored, eutrophic surface water source (Forge Pond, Granby, MA), and fractionated into quasi-homogeneous fractions. Fulvic acid (FA) and hydrophilic neutrals (HN) were the two most abundant NOM fractions that were isolated. Adsorption affinity of the isolated NOM fractions on preformed aluminum hydroxide flocs increased with increase in specific organic charge of the fractions, except for the two most highly charged fractions, FA and hydrophilic acids (HAA), which showed less adsorption affinity than expected based on their specific organic charge. Prior ozonation of FA and HN fractions resulted in a decline and an increase, respectively, in their adsorption affinity on aluminum hydroxide surface. Prior ozonation of Forge Pond raw water resulted in a progressive decline in dissolved organic carbon (DOC) removal by alum coagulation with increase in ozone dose. It appeared that ozone applied to raw water reacted preferentially with the humic fraction of NOM, resulting in the detrimental effects of ozonation on subsequent NOM removal by alum coagulation being magnified. Forge Pond raw water was pre-coagulated to remove humic substances. Ozonation of the pre-coagulated water demonstrated the beneficial effects of ozonation on the removal of non-humic NOM through alum coagulation. A strategy for staged coagulation with intermediate ozonation was proposed for waters containing both humic and non-humic NOM for maximum DOC and specific UV absorbance at 254nm (SUVA) removal.     

Removal of THM precursors by coagulation or ion exchange

The removal of natural organic matter (NOM) from drinking water supplies can be achieved by different processes, among them coagulation and adsorption. Synthetic waters made from concentrates of humic substances from reservoir and river waters were tested in the laboratory for ease of removal of NOM by coagulation with cationic organic polymers and with alum, and by adsorption on anion exchangers. For polymers such as high molecular weight polydiallyldimethylammonium chloride (polyDADMAC) and cationic polyacrylamides of high charge, performance was nearly as effective as alum, with colour removals 86–100% of those obtained for alum. Ion exchange using the best commercially available resins designed for this purpose, a gel polystyrene and a macroporous acrylic resin, was more effective than alum treatment for two of the natural waters studied, but inferior for a third. The resins were overall superior to cationic polymers.

The NOM was separated into four fractions based on hydrophobic and hydrophilic properties. Alum was not as effective as ion exchange for the elimination of individual ionic NOM fractions. It was better than cationic polymers for removal of humic and fulvic acids, although polyDADMAC was as good for one water. For the removal of charged compounds alum then polyDADMAC were the best performers for that water. Unequivocal evidence was obtained that coagulants remove material that is not adsorbed by resins, and vice versa. A combination of coagulation with a cationic polymer and adsorption by an anion exchanger removed essentially all of the NOM. The preference of the coagulants was for the larger, more hydrophobic molecules, and of resins for smaller highly charged hydrophilic molecules. Each fraction had trihalomethane formation potentials in the range 11–24 μg/mg, except for one water that was more reactive. Hence, the actual amount of each fraction in the original water becomes a crucial factor.     

Chloroform production from the chlorination of aquatic humic material: The effect of molecular weight, environment and season

Humic material from various aqueous environments and from laboratory microbial cultures was segregated into humic and fulvic acid fractions and then each fraction was separated into eight molecular weight ranges by ultrafiltration. The fractionated material was then chlorinated in aqueous solution and the amount of chloroform produced was measured. Chloroform concentration per unit weight humic material passed through a maximum at molecular weight about 20,000–30,000 for the fulvic acids, whereas the CHCl₃ concentration decreased with increasing molecular weight above 20,000–30,000 for the humic acids. Only minor fluctuations in chloroform concentrations were apparent for samples from various aqueous environments (lake, river, stream, swamp, microbial) and for samples from a single environment obtained during different seasons of the year. Based on the total amount of material isolated from the original samples and the chloroform production per unit weight, the major chloroform precursors in aquatic humic material were the low molecular weight (< 30,000) fulvic acid fractions. Unfortunately, because of their low molecular weight and high surface activity, these fractions will probably prove to be the most difficult to remove by standard water treatment processes.     

Copper catalysis in chloroform formation during water chlorination

The seminal work of Rook initiated a considerable body of research regarding the formation of trihalomethanes (THMs) and other by-products of chlorine-based disinfection. Since that time, a broad spectrum of compounds has been identified as precursors to THM formation. More recently, it has been demonstrated that the presence of copper in solution enhances THM formation. Copper is known to catalyze a number of reactions that are similar to the conventional haloform reaction. A study was therefore initiated to investigate the specific role played by copper in the formation of chloroform during chlorination of water supplies. Aqueous solutions containing a number of known THM precursors were chlorinated in the presence and absence of copper, and subjected to time-course monitoring of chloroform concentration. The results of experiments with humic acid demonstrated an apparent catalytic effect on the part of copper in chloroform formation. To examine the role of copper in greater detail, a series of experiments involving aqueous solutions of pure compounds of humic substance structural units was conducted. Of the pure compounds investigated as THM precursors, only citric acid demonstrated enhanced chloroform formation in the presence of copper. A detailed matrix of experiments conducted with citric acid as a precursor demonstrated that copper, at environmentally relevant concentrations, can have a profound effect on chloroform formation. Based on previously published information regarding the mechanism of chloroform formation from citric acid and the results of these experiments, it is hypothesized that copper promotes chloroform formation from chlorination of citric acid through catalysis of oxidative decarboxylation, and the subsequent chlorination of beta-ketoglutaric acid.     

Enhanced coagulation for high alkalinity and micro-polluted water: the third way through coagulant optimization

Conventional coagulation is not an effective treatment option to remove natural organic matter (NOM) in water with high alkalinity/pH. For this type of water, enhanced coagulation is currently proposed as one of the available treatment options and is implemented by acidifying the raw water and applying increased doses of hydrolyzing coagulants. Both of these methods have some disadvantages such as increasing the corrosive tendency of water and increasing cost of treatment. In this paper, an improved version of enhanced coagulation through coagulant optimization to treat this kind of water is demonstrated. A novel coagulant, a composite polyaluminum chloride (HPAC), was developed with both the advantages of polyaluminum chloride (PACl) and the additive coagulant aids: PACl contains significant amounts of highly charged and stable polynuclear aluminum hydrolysis products, which is less affected by the pH of the raw water than traditional coagulants (alum and ferric salts); the additives can enhance both the charge neutralization and bridging abilities of PACl. HPAC exhibited 30% more efficiency than alum and ferric salts in dissolved organic carbon (DOC) removal and was very effective in turbidity removal. This result was confirmed by pilot-scale testing, where particles and organic matter were removed synergistically with HPAC as coagulant by sequential water treatment steps including pre-ozonation, coagulation, flotation and sand filtration.     

Chlorination of humic substances in aqueous solution: Yields of volatile and major non-volatile organic halides

In this paper, we present the study of the effect of chlorination contact time, of the chlorine/carbon ratio and of the bromide concentration on the major halogenated products in the case of chlorinated humic substance solutions at neutral pH. The yields of chloroform, of trichloroacetic acid and of dichloro-acetic acid increase with the increase in reaction time and in chlorine dosage. Various values for the yield are given for chlorinated commercial humic acid solutions and for chlorinated solutions of aquatic fulvic and humic acids. The simultaneous presence of trihalomethanes precursors and bromides in the solution leads to the formation of organo-brominated products. Total trihalomethanes increase with the increase of bromide concentration.     

Simultaneous colour and DON removal from sewage treatment plant effluent: Alum coagulation of melanoidin

The aim of this study was to detect and characterise melanoidin in sewage treatment plant (STP) effluent, and to study the ability of alum coagulation to remove the colour and dissolved organic nitrogen (DON) associated with melanoidin. The melanoidin is non-biodegradable due to the complex cyclic based structure and thus it directly contributes to effluent nitrogen concentrations from the sewage treatment plant (STP). Lowering of effluent total nitrogen limits and the link between colour and chlorinated disinfection by-products have therefore driven a need to understand the structure, properties and treatability of DON species found in STP effluent.The focus of this paper is the refractory coloured, organic nitrogen compound melanoidin. Wetalla STP effluent has relatively high colour (170 mg-PtCo L⁻¹) and DON (2.5 mg L⁻¹) for a biological nutrient removal STP, owing to an industrial supply of melanoidin containing molasses fermentation wastewater. Alum coagulation jar tests were performed on synthetic melanoidin solution, STP effluent containing melanoidin (Wetalla, Toowoomba, Australia) and STP effluent free of melanoidin (Merrimac, Gold Coast, Australia) to examine the treatability of melanoidin and its associated colour and DON content when present in STP effluent.The removal of melanoidin from STP effluent resulted in significant colour and DON reduction. An alum dose of 30 mg L⁻¹ as aluminium was sufficient to reach maximum removal of colour (75%), DON (42%) and dissolved organic carbon (DOC) (30%) present in melanoidin containing STP effluent. Alum was shown to preferentially remove DON with a molecular weight >10 kDa over small molecular weight DON. Fluorescence excitation-emission matrix examination of the humic compounds present in the STP effluent indicated that melanoidin type humic compounds were more readily removed by alum coagulation than other humic 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.     

高锰酸钾与粉末炭联用处理微污染源水

烧杯试验和生产应用的结果表明,高锰酸钾与粉末活性炭联用对低温低浊微污染源水具有明显的强化处理效果,能显著降低滤后水浊度和高锰酸盐指数。但高锰酸钾与粉末活性炭的投加顺序对混凝效果有一定的影响,在投加混凝剂快速搅拌末活性炭可取得很好的强化混凝效果。生产运行结果还表明,少量剩余高锰酸钾可被粉末活性炭还原,而后被混凝过程去除。     

Effects of humic acid on physical and hydrodynamic properties of kaolin flocs by particle image velocimetry

The physical and hydrodynamic properties of kaolin flocs including floc size, strength, regrowth, fractal structure and settling velocity were investigated by in situ particle image velocimetry technique at different humic acid concentration. Jar-test experimental results showed that the adsorbed humic acid had a significant influence on the coagulation process for alum and ferric chloride. Kaolin flocs formed with the ferric chloride were larger and stronger than those for alum at same humic acid concentration. Floc strength and regrowth were estimated by strength factor and recovery factor at different humic acid concentration. It was found that the increased humic acid concentration had a slight influence on the strength of kaolin flocs and resulted in much worse floc regrowth. In addition, the floc regrowth after breakage depended on the shear history and coagulants under investigation. The changes in fractal structure recorded continuously by in situ particle image velocimetry technique during the growth-breakage-regrowth processes provided a supporting information that the kaolin flocs exhibited a multilevel structure. It was proved that the increased humic acid concentration resulted in decrease in mass fractal dimension of kaolin flocs and consequently worse sedimentation performance through free-settling and microbalance techniques.     

Enhanced coagulation using a magnetic ion exchange resin

The objective of this investigation was to examine the effectiveness of a magnetic ion exchange resin (MIEX) to enhance the coagulation of disinfection by-product precursors in nine surface waters, each representing a different element of the USEPA's 3 x 3 enhanced coagulation matrix. The effect of MIEX-pretreatment on the requisite alum dose needed for subsequent coagulation of turbidity was also evaluated. Enhanced coagulation with MIEX was found to be very effective for removing trihalomethane (THM) and haloacetic acid (HAA) precursors from the nine waters examined. THM and HAA formation potential was reduced by more than 60% in all of the waters studied; reductions approaching 90% were seen in the waters with the highest specific ultraviolet absorbance values. The residual total organic carbon concentration, ultraviolet absorbance, and THM and HAA formation potential were all substantially lower as a result of MIEX and alum treatment compared to alum coagulation alone. MIEX pre-treatment also lowered the coagulant demand of each of the waters substantially.     

Contribution à l'étude de la détermination des conditions de formation des haloformes

In recent years the presence of haloforms has been observed by some researchers in waters of various origins.The aim of this study is to determine the conditions in which chloroform is formed by chlorination of aqueous solutions of some organic compounds.The first part of this work was carried out by chlorination of synthetic basic solutions of acetone and thus enabled us to determine the reagent concentrations needed to obtain the maximum quantity of chloroform.We studied next the effect of chlorination on organic material solutions (humic acids and phenols), in the course of an oxidation treatment; the results obtained by chlorination of aqueous solutions of humic substances show that the quantity of chloroform produced passes through a maximum value which depends on the time of ozonisation. Similar results were obtained for the chlorination of phenol solutions during oxidation by the u.v. + H₂O₂ system. These results may be explained by the partial degradation of the molecules which leads in the formation of reactional intermediate precursors of the haloform reaction. We undertook at the same time the study of a rapid test allowing us to detect the presence of haloform reaction precursors in a certain sample of water.     

混凝剂中的铝形态对藻类混凝过程的影响

为了考察混凝剂中的铝形态对藻类混凝过程的影响,使用3种具有不同铝形态分布的混凝剂对含藻水进行了混凝试验。结果表明,硫酸铝由于具有较低含量的Alb,电中和能力较差,故需要较大的投量才能去除藻类,形成絮体;含藻水体系中的有机物主要是腐殖酸及富里酸类物质,微生物代谢产物(SMP)在硫酸铝作混凝剂时得到较好的去除,而腐殖酸及富里酸的去除率较低可能是造成硫酸铝混凝效果较差的原因; Alc(Al(30))在混凝中的作用机理主要是吸附架桥作用,可有效去除水体中的有机物,Al₁₃的主要作用机理是电中和作用,可以有效去除水体中的颗粒物;Al₁₃与Al₃₀由于具有形态的稳定性,其混凝过程受pH值的影响较小。絮体强度因子随着pH值的升高先增大后减小,Al₁₃作混凝剂时絮体恢复因子随pH值的升高先增大后减小,而其他两种混凝剂所形成絮体的恢复因子随pH值的升高而增大。     

Colour and turbidity removal with reusable magnetic particles—II. coagulation with magnetic polymer composites

Composite particles containing magnetic iron oxides in an insoluble polymeric matrix were used to enhance the coagulation of a turbid, coloured river water. Uncharged magnetic particles increased the turbidity removal at a given alum dose, or alternatively achieved a desired level of turbidity removal at a lower alum dose. Rates of floc formation and settling were approximately double those obtained with alum alone. Grafting linear polymers to the magnetic particles increased their effectiveness. The uncharged particles could be reused after simply washing with water. Magnetic particles with grafted chains of cationic polymers, when used in conjunction with alum, gave excellent removal of colour and turbidity and rapid settling, but required brine for regeneration. These materials were also effective in coagulating algae. When used in high doses without alum, the cationic magnetic particles initially gave good turbidity and colour removal from river water, but could not be completely regenerated     

The effect of boiling water on disinfection by-product exposure

Chloraminated and chlorinated waters containing bromide were used to determine the impact of boiling on disinfection by-product (DBP) concentrations. No significant changes were detected in the concentrations of the dihalogenated haloacetic acids (DXAAs) (i.e., dichloro-, bromochloro-, dibromoacetic acid) upon boiling of chloraminated water, whereas the levels of the trihalogenated haloacetic acids (TXAAs) (i.e., trichloro- (TCAA), bromodichloro- (BDCAA), dibromochloroacetic acid (DBCAA)) decreased over time (e.g., 9-37% for TCAA). Increased DXAA concentrations (58-68%) were detected in the boiled chlorinated sample, which likely resulted from residual chlorine reacting with DXAA precursors. TCAA concentration was unchanged after boiling chlorinated water for 1 min, but a 30% reduction was observed after 5 min of boiling. BDCAA concentrations decreased 57% upon boiling for 1 min and were completely removed after 2 min of boiling, whereas DBCAA was removed after boiling chlorinated water for 1 min. Trihalomethane concentrations were reduced in both chloraminated (74-98%) and chlorinated (64-98%) water upon boiling. Boiling chloraminated water for 1 min reduced chloroform concentration by 75%. Chloroform was reduced by only 34% in chlorinated water after a 1 min boil, which indicates that simultaneous formation and volatilization of chloroform was occurring. Most of the remaining DBPs (e.g. haloketones, chloral hydrate, haloacetonitriles) were removed by at least 90% after 1 min of boiling in both samples. These data suggest that other mechanisms (e.g., hydrolysis) may have been responsible for removal of the non-volatile DBPs and further highlight the importance of examining individual species when estimating thermal effects on DBP concentrations.     

高锰酸钾除污染生产性试验研究

生产性试验结果表明，高锰酸钾预处理能有效地去除受污水中多种有机污染物，降低水的致突变活性，并可显著地控制氯化消毒副产物，使水的致突变性由阳性转变为阴性或接近阴性，水中氯仿和四氯化碳的生成量也有显著地下降。     

Chemical aspects of coagulation using aluminum salts—I. Hydrolytic reactions of alum and polyaluminum chloride

This is the first of a two-part series of papers investigating the chemistry of Al coagulants. This paper examines hydrolysis reactions of alum and polyaluminum chloride (PAC1). Part II of the series addresses the coagulation of fulvic acid by these coagulants.

Monomeric, polymeric and precipitated Al were identified based on a timed spectrophotometric analysis. At typical A1 doses used in water treatment, alum showed no evidence of polymer formation. PAC1 consists of preformed polymers which are stable upon dilution below pH 6 and over the time frames encountered in water treatment. Solubility studies showed that alum and PAC1 precipitate to form different solid phases. Alum precipitates are adequately described by amorphous A1(OH)₃(s) solubility. The polymeric structure of PAC1 is retained upon precipitation yielding a solid phase with different light scattering characteristics, electrophoretic mobility and solubility than alum floc. A1 hydrolysis is interpreted as a coordination reaction between A1 and OH⁻. Effects of low temperature on alum are shown to be a result of changes in OH⁻ caused, in part, by the temperature dependence of the ion product of water. Hydrolysis products in PAC1 are preformed and therefore less sensitive to in situ hydrolysis than alum. Results suggest that when using alum, some of the adverse effects of low temperatures may be mitigated by an increase in pH, thereby maintaining a constant concentration of the complexing ligand, OH⁻.     

饮用水中溴化物的混凝去除及影响因素研究

在饮用水的消毒过程中，溴化物可与消毒剂反应生成具有“三致”效应的消毒副产物。为此，选择AlCl3作混凝剂，研究了混凝去除溴化物的效果及影响因素。结果表明，向模拟水样（溴化物初始浓度为0．2mg／L）中投加3-15mg／L的AlCl3，当无腐殖酸存在时对溴化物的去除率为93．3％-99．2％，当有腐殖酸存在时对溴化物的去除率为78．4％～98．4％；对于湘江原水。投加15mg／L的AlCl3时对溴化物的去除率为87．0％。在低混凝剂投量或高pH值条件下，腐殖酸的存在明显降低了对溴化物的去除率；在高混凝剂投量或低pH值条件下，腐殖酸对去除溴化物的影响较小。因此，可采用强化混凝去除饮用水中的溴化物。     

Chemical aspects of coagulation using aluminum salts—II. coagulation of fulvic acid using alum and polyaluminum chloride

This is the second of a two-part series investigating chemical aspects of coagulation using AI salts. Part I of the series examined the hydrolytic reactions of AI. In this paper, the coagulation of fulvic acid (FA) by alum and polyaluminum chloride (PACI) is examined. An Al speciation methodology was used to examine complexation reactions between Al and FA for water treatment conditions. From pH 5 to 7 and at typical coagulant doses, hydrolysis and complexation of Al is described by a simple model based on the reaction stoichiometry between AI, FA and OH⁻. Model results show that when alum is used as a coagulant, Al complexed with FA is hydrolyzed to a ligand number, This is similar to the ligand number for the prehydrolyzed PACI and explains similarities in dose requirements for these coagulants. Effects of temperature on coagulation performance are shown to be largely chemical in nature. Chemical aspects of coagulation are discussed and the importance of complex formation in coagulation is examined.     

不同分子质量区间腐殖酸的氯化反应特性研究

以自配的腐殖酸水样为研究对象,投加次氯酸钠对其进行消毒,考察了消毒过程中三卤甲烷、卤乙酸的生成量及DOC、UV254、A410、A465/A656的变化情况。结果表明,分子质量为50—100ku的腐殖酸为生成三卤甲烷和卤乙酸的最主要前体物;消毒反应后,各分子质量区间腐殖酸的DOC、UV254和A410都有不同程度的下降,且对小分子质量腐殖酸的DOC、UV254和A410的去除率高于对大分子质量腐殖酸的;A465／A656的变化表明消毒过程中腐殖酸的分子质量呈下降趋势。