Coagulation Of Humic Acid Research Articles

Coagulation behaviors of aluminum salts towards humic acid: Detailed analysis of aluminum speciation and transformation

The hydrolysis of Al-based coagulants, especially aluminum speciation and transformation, is necessary for organic matter removal by the coagulation process. The goal of this study was to investigate the efficiency and mechanism of hydrolyzed Al species in the coagulation of humic acid (HA) removal. Three aluminum coagulants have been applied to investigate HA coagulation, which are aluminum chloride AlCl3 dominated by monomeric aluminum species Ala, polyaluminum chloride PACl1 dominated by medium polymer species Alb, and commercial polyaluminum chloride PACl2 dominated by larger polymer species and/or colloidal aluminum species Alc. Results showed that the best coagulation effect on HA removal (higher than 90%) occurred at pH 6 for three aluminum coagulants and their effect decreased in the order: PACl1 > AlCl3 > PACl2. Except that, the in situ hydrolyzed aluminum species produced by AlCl3 had synergistic effects on various sites of HA, and showed good adaptability to raw water and coagulant dosage. Hydrolyzed larger polymeric aluminum species of PACl1 could selectively bind to the HA site with strong binding, especially Al13 under the weak acidic condition. While for PACl2, complexation of small and median polymeric aluminum species, charge neutralization effect of Al13, and the effect of sweep coagulation of large polymeric aluminum species were involved. Moreover, diversity of hydrolyzed aluminum species in the coagulation process presented a significantly impact on flocs characteristics. This study provided a new insight into the relationship between HA and aluminum speciation and transformation for Al-based coagulants, which can be indicative to select suitable coagulants according to the water quality in the coagulation process.

Optimized coagulation of humic acid and mineral turbidity at alkaline pH using high basicity PACl

Abstract In this study, the simultaneous removal of inorganic turbidity and organics was investigated at alkaline pH to avert the need for pH adjustment and overdosing. The aim was to compare the doses for conventional and enhanced coagulation and, consequently, arrive at optimized coagulation where both had synergistic maximum removal. High basicity PACl was used to coagulate simulated waters prepared by humic acid (HA) and kaolin. The removal of turbidity, total organic carbon (TOC), dissolved organic carbon (DOC) and UV254 was evaluated. The impact of varying input concentrations of HA and turbidity on doses was studied. The enhanced coagulation doses were higher than conventional ones. However, with an increase in input TOC, the difference between enhanced and conventional doses narrowed. The doses for optimized coagulation ranged from 2 to 9 mg Al/L. At optimized coagulation, the removal of TOC, DOC and UV254 varied from 30–85%, 30–89% and 73–91% respectively. Fourier transform infrared (FTIR) spectroscopy revealed the presence of Si-O-C bond. The interactions of unsaturated bonds of hydrophobic organics to inorganic clay were possibly favoured over hydrophilics. HA agglomeration reduced coagulant consumption as the input TOC increased. It was concluded that instead of a stoichiometric approach, a modified dosing approach can be applied for limiting underdosing and overdosing while ensuring maximum removal of impurities.

Minimization of halogenated DBP precursors by enhanced PACl coagulation: The impact of organic molecule fraction changes on DBP precursors destabilization with Al hydrates

The destabilization of halogenated disinfection-by-product (DBP) precursors by coagulation are mostly subjected to Al speciation of polyaluminum chloride (PACl) and the fraction of dissolved organic matter (DOM), which significantly affect the minimization of halogenated DBP precursors, such as trihalomethane (THM) and haloacetic acids (HAA), in post-chlorination. In this study, the destabilization of DOM in the solution of humic acid (HA) with and without algogenic organic matter (AOM) using two PACl coagulants with different Al speciation was investigated, along with the identification of optical properties for DOM fractions. Additionally, total THM and HAA formation potential of the supernatant before and after coagulation-sedimentation were determined. The results showed that high polymeric Al-containing PACl (PACl-H, 66% Al13) outcompetes in destabilizing HA than commercial PACl (PACl-C, 29% Al13, 32% Al(OH)3). However, the removal of DOM in HA/AOM mixture by both PACl coagulants are significantly suppressed with greater removal of humic-like and fulvic-like substances than aromatic protein-like substances after coagulation-sedimentation, where PACl-C shows superiority in the removal of hydrophobic and hydrophilic substances with MW around 1 kDa than PACl-H. In the absence of AOM, total THM and HAA formation potential were effectively reduced for HA coagulation by both PACl, but vice versa with the presence of AOM, especially for cellular organic matter (COM). Minimization of halogenated DPB precursors by coagulation are predominated by destabilized hydrophilic molecule fractions with Al hydrates. It is concluded that PACl-H favors charge neutralization to destabilize total carbonaceous DBP (C-DBP) precursors in HA or HA/AOM mixture and the corresponding C-DBP formation potential is lower compared to PACl-C that predominates adsorption and co-precipitation in destabilizing C-DBP precursors.

Coagulation of humic acid and kaolin at alkaline pH: Complex mechanisms and effect of fluctuating organics and turbidity

Coagulation was performed on synthetic test waters prepared with different concentrations of humic acid (HA) and kaolin to simulate organics and turbidity found in natural surface waters. The alkalinity of the test waters was high (180–205 mg/L) and high basicity PACl was used to coagulate the impurities as it is best suited for high alkalinity waters. Separate removal mechanisms of HA and kaolin has been dealt in detail by many researchers but in this paper the simultaneous removal mechanisms are stressed upon. Synthetic test waters were chosen instead of real surface waters to incorporate the effects of fluctuating organics and turbidity to have better insights into the removal mechanisms. Jar test was used to evaluate the removal efficiency of TOC, DOC, UV254 and turbidity. Zeta potential, particle/floc size, pH and alkalinity were also evaluated before and after the coagulation to investigate the charge neutralisation capacity of PACl at alkaline pH. The pH at optimum doses varied from 6.5 to 8 suggesting removal dominantly by sweep coagulation. The complete charge neutralisation was not possible which was indicated by the negative zeta potential even at optimum doses as some residual TOC (0.5–2 mg/L) and DOC (0.4–1.4 mg/L) remained in the treated water. The residual turbidity at optimum doses was <1 NTU. The complex removal mechanisms of HA and kaolin for these test waters were further elucidated by using three adsorption models: Langmuir, Freundlich and BET model. The BET adsorption model showed highest R2 values suggesting removal by multilayer adsorption.

Coagulation behavior of humic acid in aqueous solutions containing Cs+, Sr2+ and Eu3+: DLS, EEM and MD simulations.

The coagulation behaviors of humic acid (HA) with Cs+ (10-500 mM), Sr2+ (0.8-10.0 mM) and Eu3+ (0.01-1.0 mM) at different pH values (2.8, 7.1 and 10.0) were acquired through a dynamic light scattering (DLS) technique combined with spectroscopic analysis and molecular dynamic (MD) simulations. The coagulation rate and the average hydrodynamic diameter (<Dh>) increased significantly as the concentration of nuclides increased. <Dh> could be scaled to time t as <Dh>∝ ta at higher Sr2+ concentrations, which shows that HA coagulation is consistent with the diffusion-limited colloid aggregation (DLCA) model. Trivalent Eu3+ induced HA coagulation at a much lower concentration than bivalent Sr2+ and monovalent Cs+. The coagulation value ratio of Sr2+ and Eu3+ to Cs+ is almost proportional to Z-6, indicating that the HA coagulation process is generally consistent with the Schulze-Hardy rule. Spectroscopic analysis indicated that the complexation between nuclides and carboxylic/phenolic groups of HA molecules played important roles in the coagulation of HA. MD modelling suggested that Sr2+ and Eu3+ ions increased the coagulation process through the formation of intra- or inter-molecular bridges between negatively charged HA molecules, whereas for Cs+, no inter-molecular bridges were formed. This work offers new insight into the interactions between HA and radionuclides and provides a prediction for the roles of HA in the transportation and elimination of radionuclides in severely polluted environments.

Lignin cationization with glycidyltrimethylammonium chloride aiming at water purification applications

Hardwood organosolv lignin (OSL) and enzymatic hydrolysis lignin (EHL) from softwood were cationized by glycidyltrimethylammonium chloride (GTAC) as new lignin starting materials for the reaction. The products were in detail characterized by 31P-NMR to elucidate the reactivity of different lignin functionalities in cationization with GTAC. For OSL, a high cationization level (degree of substitution 0.74) was reached leading to a water-soluble product. For EHL, low solubility and lower reactivity were observed, likely due to the high saccharide content. Further, lower reactivity of the guaiacyl type lignin present in softwood, compared to syringyl type lignin in hardwoods, which was shown to react efficiently during the derivatization of OSL, probably played a role. In parallel to cationization, an increase of carboxylic acids (from 0.03 up to 0.55mmol/g) in the lignin was observed as an unexpected side reaction, possibly as a result of alkaline oxygen oxidation. The applicability of the cationized lignins was tested for water purification applications in three model systems which have only sparingly been studied with cationized lignins. GTAC-OSL and GTAC-EHL were found promising for sulfate removal, with sulfate sorption capacities of up to 54mg/g. GTAC-OSL was also found suitable for promoting kaolin settling and to some extent for humic acid coagulation.

Amine-Cross-Linked Lignin-Based Polymer: Modification, Characterization, and Flocculating Performance in Humic Acid Coagulation

In this study, a lignin-based flocculant (LNF) was synthesized by grafting amine groups into alkali lignin containing papermaking sludge. Characterization of LNF, such as FTIR, zeta potential, cationic degree, viscosity, and molecular weight, showed that the product was a cationic polymer with high solubility. LNF was used with aluminum sulfate (AS) and polyaluminum chloride (PAC) in humic acid coagulation to demonstrate its efficiency. Coagulation behavior and floc properties of LNF+PAC and LNF+AS dual-coagulant were comparatively evaluated. Results showed that the coagulation aid effect of LNF was independent of aluminum species. Addition of LNF could enhance humic acid removal efficiency and floc properties including size, strength, and fractal dimension significantly. The effect of solution pH on coagulation processes was also studied. Dual-coagulants showed the same variation trend as that of aluminum-based coagulants but enhanced coagulation performance during the investigative pH range. Flocs forme...

The coagulation characteristics of humic acid by using acid-soluble chitosan, water-soluble chitosan, and chitosan coagulant mixtures

Chitosan is a potential substitute for traditional aluminium salts in water treatment systems. This study compared the characteristics of humic acid (HA) removal by using acid-soluble chitosan, water-soluble chitosan, and coagulant mixtures of chitosan with aluminium sulphate (alum) or polyaluminium chloride (PACl). In addition, we evaluated their respective coagulation efficiencies at various coagulant concentrations, pH values, turbidities, and hardness levels. Furthermore, we determined the size and settling velocity of flocs formed by these coagulants to identify the major factors affecting HA coagulation. The coagulation efficiency of acid- and water-soluble chitosan for 15 mg/l of HA was 74.4% and 87.5%, respectively. The optimal coagulation range of water-soluble chitosan (9–20 mg/l) was broader than that of acid-soluble chitosan (4–8 mg/l). Notably, acid-soluble chitosan/PACl and water-soluble chitosan/alum coagulant mixtures exhibited a higher coagulation efficiency for HA than for PACl or alum alone. Furthermore, these coagulant mixtures yielded an acceptable floc settling velocity and savings in both installation and operational expenses. Based on these results, we confidently assert that coagulant mixtures with a 1:1 mass ratio of acid-soluble chitosan/PACl and water-soluble chitosan/alum provide a substantially more cost-effective alternative to using chitosan alone for removing HA from water.

Effects of UV radiation on humic acid coagulation characteristics in drinking water treatment processes

Abstract Humic acid (HA) commonly exists in natural waters and drinking water treatment processes. The effects of UV light radiation on the coagulation of HA were investigated in this paper. It was determined that UV light radiation could effectively improve the removal of HA at pH above 6.0. The concentration of residual HA in the coagulated water was in the range of 1.5–3.0 mg/L, which was significantly lower compared to that without pretreatment. However, in waters tested with pH below 5.5, the UV light radiation showed an adverse effect on HA removal using coagulation, which might be connected to its high oxidation function under acidic conditions. The zeta potential of the HA solution with UV light radiation was approximately 10 mv higher compared to that without pretreatment at pH above 6.0; while its apparent diameters and heights increased from less than 130 nm and 0.5–3.5 nm to 100–240 nm and 1.0–4.5 nm respectively, after 2.0 h of UV light radiation as the aggregation of HA. The compressed double electric layer caused by the formation of positive charged sites after UV light radiation was considered to be the primary factor that led to the enhanced removal of HA in the following coagulation process.

Fate of hydrolyzed Al species in humic acid coagulation

The hydrolysis of Al-based coagulants in acidic conditions is necessary for the removal of organic matter by the coagulation/sedimentation process. However, interactions between hydrolyzed Al species and organic matter are complicated and this makes it difficult to optimize coagulant dosing for organics removal. The goal of this study was to investigate the reactions of hydrolyzed Al species in the coagulation of organic matter. Two polyaluminum chloride (PACl) coagulants, a commercial product with sulfate (PACl-C) and lab-prepared material (PACl-Al13) containing 7% and 96% of total Al as Al13, respectively, have been applied to investigate the coagulation of humic acid (HA). At pH 6, a lower dosage of PACl-Al13 than of PACl-C was required for optimized HA removal through coagulation/sedimentation due to the strong complexation and charge neutralization by Al13. Observation of the coagulation process using wet scanning electron microscopy showed that PACl-C produced both clustered flocs and linear precipitates in the presence of sulfate while PACl-Al13 produced curled precipitates due to the formation of intermolecular complex, when both coagulants were added at the optimum doses. Investigation of Al–HA floc by 27Al-NMR and Al 2p XPS suggested that monomeric Al (Alm) was hydrolyzed into Al(OH)3 with tetrahedron for PACl-C coagulation while a half of Al13 slowly decomposed into octahedral Al–HA precipitates for PACl-Al13 coagulation. Meanwhile, C ls XPS indicated that aromatic CC of HA was preferentially removed from solution to Al–HA flocs for both PACl-C and PACl-Al13 coagulation. It was concluded that Al–HA complexation strongly affects the reaction pathways for Al hydrolysis and the final nature of the precipitates during PACl coagulation of HA and that the hydrolysis products are also strongly affected by the characteristics of the PACl coagulant.

Impacts of salt type and concentration on coagulation of humic acid and silica

Zeta potential distributions of model waters containing silica, humic acid, and differing ionic composition were evaluated. These distributions showed that under high ionic strength and in the presence of divalent cations, positive colloids exist in suspension with neutral and negative colloids. Positive colloids do not form at lower ionic strength or when polyvalent cations are absent. The existence of the positive colloids in suspension with the negative colloids suggests that, while electrodynamically unstable, some stabilizing factor is preventing coagulation. This stabilizing factor is likely adsorbed humic acid causing steric hindrance. Further tests indicated that under the conditions that lead to the existence of positive colloids, removal of humic acid by ferric chloride coagulation is diminished as compared to coagulation in lower ionic strength water or water containing just sodium chloride as the ionic matrix. As positively calcium–humic complexes can increase fouling of desalting membranes through the formation of densely packed fouling layers, understanding the mechanisms of coagulation in high ionic strength waters is crucial to improving performance of desalination operations.

Effect of Al species in polyaluminum silicate chloride (PASiC) on its coagulation performance in humic acid–kaolin synthetic water

The relative importance of three different Al species (Ala, Alb and Alc) in polyaluminum silicate chloride (PASiC) was investigated in terms of coagulation removal efficiency and floc characteristic during the coagulation of humic acid–kaolin clay (HA–Kaolin) synthetic solution. Coagulation performance of PASiC (Al/Si molar ratio of 10:1) was also compared with that of polyaluminum chloride (PAC). Three PASiC coagulants with Ala, Alb and Alc dominant in one of them were denoted as PASiCa, PASiCb and PASiCc, respectively. The results showed that PASiCb performed the best turbidity and DOC removal, followed by PASiCc and PASiCa, while PASiCb and PASiCc removed UV254 more efficiently than PASiCa. At low dosages (1–4mg/L), flocs formed by PASiCb and PASiCc coagulation had higher zeta potential than those by PASiCa coagulation. However, order of zeta potential was PASiCa>PASiCc>PASiCb at high dosage of 18mg/L. Both coagulation efficiency and zeta potential were observed to be maximal at pH of 6. Zeta potential of formed flocs formed by PASiCc coagulation was the highest followed by PASiCb and PASiCa (in decreasing order) in pH range of 4–8, while PASiCa coagulation showed highest zeta potential followed by PASiCb and PASiCc at pH 9. The average size of flocs formed by three PASiC coagulants varied according to the following order: PASiCa>PASiCb>PASiCc. The floc equivalent diameters obtained by PASiCb coagulation were invariable with pH variation. Strength factors and recovery factors of flocs formed by PASiCc coagulation were larger than those by PASiCa and PASiCb coagulation within all investigated pHs.

Aggregation of nano-sized alum–humic primary particles

In order to understand the mechanism of floc formation and growth in coagulation process, effect of zeta potential and surface characteristic of nano sized primary particles on coagulation efficiency were investigated by coagulation of humic acid with alum in this study. It was demonstrated that only 1min rapid mixing was enough for adsorption of humic acid onto the precipitates of alum, and 15min flocculation (slow mixing) only induced the formation and growth of flocs. The primary particle size of alum–humic flocs was near 50nm and spherical. Mathematical model deduced from Derjaguin–Landau–Verwey–Overbeek (DLVO) theory showed that the formation of micro-flocs (or lag time) was determined by the square value of zeta potential of nano-sized primary particles and intensity of Brownian motion, which is closely related to water temperature. There was an absolute critical zeta potential, i.e. 13.5mV in this study, determining whether two nano-sized particles could overcome the energy barrier consisted of Van der Waals force and electrical double layer repulsion force to allow floc formation to occur at a certain temperature. The Brownian motion determined whether the nano-sized primary particles (aluminum hydroxide precipitates with humic acid) had the opportunity to overcome the repulsive force and cement with each other. Low coagulation efficiency at high latitude area in winter is caused by low collision frequency, which is mainly attributed to the low intensity of Brownian motion at a low temperature. Furthermore, it was demonstrated that aggregation of micro-flocs or their clusters significantly depended on activated sites on the primary particles rather than the zeta potential of primary particles when sweep flocculation dominated the coagulation mechanism if the size of flocs was larger than some value.

The impacts of coagulant aid-polydimethyldiallylammonium chloride on coagulation performances and floc characteristics in humic acid–kaolin synthetic water treatment with titanium tetrachloride

Coagulation of humic acid–kaolin synthetic water was conducted with Titanium tetrachloride (TiCl 4) and/or polydimethyldiallylammonium chloride (PD) to assess the effect of coagulant aid PD on coagulation behavior and floc characteristics. Coagulation behavior was investigated in terms of the reduction of turbidity and the removal of natural organic matter (NOM). The results show that the humic acid (HA) removal increased with the addition of PD depending on the doses of it and TiCl 4, and the HA removal was more enhanced by PD at low TiCl 4 doses than at higher ones. In addition, PD–TiCl 4 (PD dosed firstly, followed by TiCl 4 addition) gave better turbidity and HA removal than TiCl 4–PD (TiCl 4 dosed firstly, followed by PD addition) in this investigation. The growth, breakage, regrowth and fractal nature of flocs was investigated by use of Mastersizer 2000. TiCl 4 plus cationic polymer PD exhibited an apparent improvement on floc size and floc grow rate, and they were both in the following order: PD–TiCl 4 > TiCl 4–PD > TiCl 4. Compared with TiCl 4, the dual-coagulants significantly improved the floc recoverability. Besides, the dual-coagulants gave more compact floc structure than TiCl 4 coagulant at each coagulant dose under investigation and the values of fractal dimension ( D f) were in the order of TiCl 4–PD > PD–TiCl 4 > TiCl 4.

Effects of advanced oxidation pretreatment on residual aluminum control in high humic acid water purification

Due to the formation of disinfection by-products and high concentrations of Al residue in drinking water purification, humic substances are a major component of organic matter in natural waters and have therefore received a great deal of attention in recent years. We investigated the effects of advanced oxidation pretreatment methods usually applied for removing dissolved organic matters on residual Al control. Results showed that the presence of humic acid increased residual Al concentration notably. With 15 mg/L of humic acid in raw water, the concentrations of soluble aluminum and total aluminum in the treated water were close to the quantity of Al addition. After increasing coagulant dosage from 12 to 120 mg/L, the total-Al in the treated water was controlled to below 0.2 mg/L. Purification systems with ozonation, chlorination, or potassium permanganate oxidation pretreatment units had little effects on residual Al control; while UV radiation decreased Al concentration notably. Combined with ozonation, the effects of UV radiation were enhanced. Optimal dosages were 0.5 mg 0 3/mg C and 3 hr for raw water with 15 mg/L of humic acid. Under UV light radiation, the combined forces or bonds that existed among humic acid molecules were destroyed; adsorption sites increased positively with radiation time, which promoted adsorption of humic acid onto polymeric aluminum and Al(OH) 3(s). This work provides a new solution for humic acid coagulation and residual Al control for raw water with humic acid purification.

Oxidation and coagulation of humic substances by potassium ferrate

Ferrate (FeO₄²⁻) is believed to have a dual role in water treatment, both as oxidant and coagulant. Few studies have considered the coagulation effect in detail, mainly because of the difficulty of separating the oxidation and coagulation effects. This paper summarises some preliminary results from laboratory-based experiments that are investigating the coagulation reaction dynamically via a PDA instrument, between ferrate and humic acid (HA) at different doses and pH values, and comparing the observations with the use of ferric chloride. The PDA output gives a comparative measure of the rate of floc growth and the magnitude of floc formation. The results of the tests show some significant differences in the pattern of behaviour between ferrate and ferric chloride. At pH 5 the chemical dose range (as Fe) corresponding to HA coagulation was much broader for ferrate than ferric chloride, and the optimal Fe dose was greater. Ferrate oxidation appears to increase the hydrophilic and electronegative nature of the HA leading to an extended region of charge neutralisation. A consequence of the ferrate oxidation is that the extent of HA removal was slightly lower ( approximately 5%) than with ferric chloride. At pH 7, in the sweep flocculation domain, ferrate achieved much greater floc formation than ferric chloride, but a substantially lower degree of HA removal.

The effectiveness of humic acid coagulation with the use of cationic polyacrylamides

The chemical coagulation process is a popular method for eliminating the precursors of disinfection by-products. This study presents the results of a laboratory experiment which investigates the use of cationic polyacrylamide copolymers (CPAMs) as primary coagulants in the purification of solutions containing humic acids (HA). A number of polymers with various molecular weight and charge density were tested. The optimal doses were determined by colloidal titration. The effectiveness of coagulation-flocculation was determined by jar test method. The post-coagulation suspension was separated by filtration through cellulose filter paper. The experiment showed that charge neutralization destabilizes organic colloidal particles. An inversely proportional relationship was observed between the optimal dose and polymer charge density. The effectiveness of UV(254) reduction (52-81%) and colour removal (51-88%) was determined by the effectiveness of filtration in removing post-coagulation turbidity, as well as by the type of applied polymer. The results of the study suggest that the use of CPAMs with high charge density and low molecular weight enables effective removal of humic acids from water in the coagulation and filtration process.

Effect of shear force and solution pH on flocs breakage and re-growth formed by nano-Al 13 polymer

The breakage and re-growth of flocs formed by polyaluminum chloride (PAC) and the Al 13O 4 (OH) 24 7+ (Al 13 for short) polymer were comparatively evaluated for the coagulation of humic acid (HA). A series of jar experiments were conducted to investigate the impacts of shear rate and solution pH on flocs breakage and re-aggregation potential. Results indicated that the responses of flocs to the increasing shear force and solution pH depend on the coagulant used. The ability of flocs to resist breakage decreased with the increasing shear rate. For all levels of shear force investigated in this study, the flocs formed by Al 13 polymer were weaker than those of PAC, whereas Al 13 polymer displayed a better recoverability than PAC. The similar results were obtained when pH of solution was changed. The flocs generated in acidic conditions were stronger and more recoverable than those generated in alkaline conditions no matter which coagulant was used.

Coagulation of humic acid by PACl with high content of Al 13: The role of aluminum speciation

The role of aluminum speciation in coagulation–flocculation of humic acid (HA) by polyaluminum chloride (PACl) with high content of Al 13 was investigated using 27Al NMR spectroscopy, solid-state 27Al NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and Al-Ferron method. Experimental results show that, in the coagulation process, the Al 13 polymers are the dominant species in acidic pH and some of them change to Al precipitates at higher pH. The mechanism of HA removal is directly related to the form of aluminum in solution. The maximum removal of the HA is found to occur in the pH range from 5.0 to 6.0, which means that charge neutralization by Al 13 polymer is the main mechanism of coagulation at slightly acidic pH. The results of zeta potential and solid-state 27Al NMR spectroscopy of the flocs also confirm that positive polymers are very effective in charge neutralizing with HA molecules. Adsorption and sweep coagulation of HA by amorphous Al(OH) 3(s) play an important role at pH > 6.0 or over dosing.

Characterization of floc size, strength and structure in various aluminum coagulants treatment

Flocs generated in various aluminum coagulants treatment exhibit difference in size, strength and structure. The formation, breakage and re-formation of flocs were investigated by using a laser diffraction instrument (Malvern Mastersizer 2000, Malvern, UK). Different Al coagulants – conventional Al salt (AlCl 3), polyaluminum chloride (PAC-1) and the purified polyaluminum chloride (PAC-2) – were investigated for the coagulation of humic acid (HA). The results showed the properties of HA flocs depend on which species of aluminum used. The monomeric and dimeric aluminum species (denoted as Al mono) formed the largest and strongest HA flocs with longest growth time. The HA flocs formed by Al 13O 4(OH) 7+ 24 (Al 13 for short) is the smallest and weakest. The properties of HA flocs made it possible to investigate the relationship between the flocs growth process and aluminum species.