Abstract: Compared with traditional aluminum salts, polyaluminum chloride (PACl) has better coagulation-flocculation performance in turbidity removal. However, it is still inferior to organic polymers in terms of bridging function. In order to improve the aggregating property of PACl, different composite PACl flocculants were prepared with various organic polymers. The effect of organic polymer on the distribution of Al (III) species in composite flocculants was studied using ^{27} Al NMR and Al-ferron complexation methods. The charge neutralization and surface adsorption characteristics of composite flocculants were also investigated. Jar tests were conducted to evaluate the turbidity removal efficacy of organic polymer modified composite…flocculants. The study shows that cationic polymer and anionic polymer have significant influences on the coagulation-flocculation behaviors of PACl. Both cationic and anionic polymers can improve the turbidity removal performance of PACl but the mechanisms are much different: cationic organic polymer mainly increases the charge neutralization ability, but anionic polymer mainly enhances the bridging function.
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Abstract: Based on numerous latest references, the current developments in surface complexation, surface precipitation and the corresponding models (SCMs and SPMs), were reviewed. The contents involved comparison on surface charge composition and layer-structure of solid-solution interface for the classical 1-pK and 2- pK models, In addition, the fundamental concept and relations of the new models, i.e., multi-site complexation (MUSIC) and charge -distribution (CD) MUSIC models were described as well. To avoid misuse or abuse, it must be emphasized that the applicability nd limitation for each model should be considered carefully when selecting the concerned model(s). In addition, some new powerful techniques…for surface characterization and analysis applied to model establishment and modification were also briefly introduced.
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Abstract: This article discusses the influential factors on Al_{13} separation considering the interaction of sulfate with various polyaluminum chloride (PACl). The experimental results showed that the basicity (B=[OH]/[Al]), the concentration of PACl and Al/SO_4 ratio exhibited significant roles in the PACl-sulfate reaction. It indicated that different species in various PACl underwent different reaction pathway with sulfate. The Al_c , colloidal species, formed precipitation quickly with sulfate, while Al_b , oligomers and polymers, undergoes slow crystallization. And Al_a , monomers, reacts with sulfate to form soluble complexes. The kinetic difference of reaction made it possible to realize the separation of Al_b and…further purification. The decrease of Al_a resulted in the limit of ferron method was also mentioned.
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Abstract: Water samples collected from early March 2001 to the end of April 2002 at the branch of Pearl River around the Guangzhou City were analyzed for its micro-polluted characteristics. The coagulation behavior of polyaluminum chlorides (PACls) was then examined focusing on the effect of primary water quality and speciation distribution. The results showed that PACls exhibit better coagulation efficiency than alum in accordance with the different speciation.The turbidity removal property of PACls is evidently better than alum at Iow dosage. While in neutral zone (about 6.5–7.5), the turbidity removal of PACls decreases owing to the restabilization of particles at higher…dosage. The organic matters in raw water exhibit marked influence on coagulation. In acidic zone, organic matters complex with polymer species and promote the formation of flocs. With an increase in pH, the complexation of organics with polymer species gradually decreases, and the removal of organics mainly depends on adsorption. The effect is evidently improved with the raise of B value.
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Keywords: PACl, micro-polluted river water, DOC, coagulation efficiency
Abstract: FT-IR, Raman microscopy, XRD, {29}^Si and {27}^Al MAS NMR, were used to investigate changes in surface properties of a natural illite sample after acid-base potentiometric titration. The characteristic XRD lines indicated the presence of surface Al-Si complexes, preferable to Al(OH)_3 precipitates. In the microscopic Raman spectra, the vibration peaks of Si-O and Al-O bonds diminished as a result of treatment with acid, then increased after hydroxide back titration. The varied ratio of signal intensity between {IV}^Al and {VI}^At species in {27}^Al MAS NMR spectra, together with the stable BET surface area after acidimetric titration, suggested that edge faces and basal…planes in the layer structure of illite participated in dissolution of structural components. The combined spectroscopic evidence demonstrated that the reactions between illite surfaces and acid-leaching silicic acid and aluminum ions should be considered in the model description of surface acid-base properties of the aqueous illite.
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Abstract: The sorption behavior was determined for a model polycyclic aromatic hydrocarbon (PAH), i.e., phenanthrene (PHN), from water to three humic acids (HAs) and three sediments in different reacting time. The chemical compositions of HA samples were measured using cross polarization magic angle spinning carbon-13 (CPMAS^{13} C) NMR along with elemental analysis. The dissolved humic substances dissociating from solid HAs and sediments were characterized by ^1 H NMR. The experiments indicated that the sorption modes and mechanisms of natural sorbents for PHN varied significantly between short (<7 d) and long contact time and the reaction time should be taken into consideration…in studying the overall sorption process. The sorption capacity (K'_1 ) and exponent (n) might be relative to the properties of dissolved humic materials in initial stage but the solid aromatic organic matter after long time reaction. According to the experiments performed in this investigation and the previous researches, a conceptive sorption model was established.
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Abstract: Typical sediments from Taihu Lake, a meso-to-hypereutrophic lake, were collected and examined on the basis of P-fractionation by sequential extraction scheme. Sedimentary inorganic phosphorus were fractioned into four forms and the rank order according to the mean concentration of P-fractions in Taihu Lake was NaOH-P > BD-P > HCI-P > NH_4 Cl-P. The concentrations of BD-P were linearly correlated with the content of active Fe (R^2 = 0.96). Also, the linear relationship between the sum of BD-P and NaOH-P and the sum of active Fe and active Al content was observed within the six sediments investigated (R^2 = 0.96). Moreover,…the bio-available phosphorus (BAP) content was estimated by the sum of NH_4 CI-P, BD-P, and NaOH-P, viz. BAP = NH_4 CI-P + NaOH-P + BD-P. In Taihu Lake, the BAPcontents are ranging from 0.10 mg/g dw to 1.25 mg/g dw, and average 0.40 mg/g dw for all sediment samples. The relative contributions of BAP to total sedimentary phosphorus (TP) and inorganic sedimentary phosphorus (IP) range from 18.67% to 50.79% (33.61% on average) and from 52.82% to 82.09% (67.81% on average), respectively.
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Keywords: phosphorus fractionation, bio-availability, sediment, Taihu Lake
Abstract: Systematic investigation on enhancing removal of natural organic matter (NOM) using inorganic polymer flocculant (IPF), polyaluminum chloride (PACI) and polyacrylamide (PAM) was performed in a typical south-China source water. Enhanced coagulation and applying polymer flocculant-aid were compared through jar tests and pilot tests. Raw water and settled water were characterized and fractionated by resin adsorption. The results show that DOC composes major part of TOC. The DOC distribution keeps relatively stable all around the year with typical high amounts of the hydrophilic matter around 50%. The distribution between HoB, HoA and HoN varies and undergoes fluctuation with the year round.…During the summer season, the HoN becomes gradually the major part in hydrophobic parts. PACl with the species being tailor-made shows little pH effect during coagulation. The enhanced coagulation dosage for PACl could be 4.5 mg/L for the typical source water. The highest TOC removal achieved 31%. To be economically, 3 mg/L dose is the optimum dosage. Although hydrophilic fractions of NOM of both treatment strategies are removed about 30%, NOM causing UV_{254} absorbance were well removed (about 90%). Hydrophobic bases and acids fractions are much more removed under enhanced conditions. The hydrophilic fraction could be better removed using PAM, the polymer coagulant aid.
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Keywords: enhanced coagulation, PACI, PAM, NOM fractionation
Abstract: Ozone plays an important role as a disinfectant and oxidant in potable water treatment practice and is increasingly being used as a pre-oxidant before coagulation. The purpose of this study is to obtain insight into the mechanisms that are operative in pre-ozonized coagulation. Effects ofpre-ozonation on organic matter removal during coagulation with IPF-PACl were investigated by using PDA (photometric disperse analysis), apparent molecular weight distribution and chemical fractionation. The dynamic formation of flocs during coagulation process was detected. Changes of aquatic organic matter (AOM) structure resulted from the influence of pre-ozonation were evaluated. Results show that dosage of O_3 and…characteristics of AOM are two of the major factors influencing the performance of O_3 on coagulation. No significant coagulation-aid effect of O_3 was observed for all experiments using either AlCl_3 or PACl. On the contrary, with the application of pre-ozonation, the coagulation efficiency of AlCl_3 was significantly deteriorated,reflected by the retardation of floc formation, and the removal decreases of turbidity, DOC, and UV_{254} . However, if PACl was used instead of AlCl_3 , the adverse effects of pre-ozonation were mitigated obviously, particularly when the O_3 dosage was less than 0.69 (mg O_3 /mg TOC). The difference between removals of UV_{254} and DOC indicated that pre-ozonation greatly changed the molecular structure of AOM, but its capability of mineralization was not remarkable. Only 5% or so DOC was removed by pre-ozonation at 0.6–0.8 mg/L alone. Fractionation results showed that the organic products of pre-ozonation exhibited lower molecular weight and more hydrophilicity, which impaired the removal of DOC in the following coagulation process.
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Abstract: The capillary model was used to analyze the hydraulic conditions in the deep bed filtration process. The physicochemical interaction forces between the filter media and suspended particles and their influence on deep bed filtration process were also studied theoretically. Through the comparison of the hydraulic and physicochemical forces, the key influencing factors on the filtration process were proposed and investigated. Pilot study of the micro-flocculation deep bed filtration was carried out in the No. 9 Potable Water Treatment Plant of Beijing, and the experimental results of hydraulic head loss, particle distribution and entrapment were presented. The theoretical prediction was reasonably…consistent with the experimental results under different conditions, which indicated that the regulation and control of micro-flocculation and deep bed filtration could be realized by the evaluation of the physicochemical interactions. Further theoretical and experimental research should be carried out to investigate the interaction mechanism and its application in the deep bed filtration and other cases.
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