Floc Growth Rate Research Articles

Enhancing floc size and strength with a hybrid polymer of zinc oxide, acrylamide, and tannin in textile wastewater.

This study involved synthesising new hybrid polymers called ZOPAT, made up of zinc oxide, acrylamide, and tannin, using a blended technique. The effectiveness of ZOPAT in treating textile wastewater was then tested by measuring floc growth rate, flocculation index, strength factor, and recovery factor under optimised conditions. The study also identified the zeta potential, morphology, elemental composition, and functional groups of the polymers. Response surface methodology determines the optimal pH and ZOPAT dose, resulting in 93% colour, 80% chemical oxygen demand (COD), 100% turbidity, and suspended solids (SS) removal at pH 9.22 and 737 mg/L ZOPAT. The study found that ZOPAT was more effective than commercial Polyaluminium chloride in reducing colour and COD, producing larger and stronger flocs, and requiring a shorter coagulation time of 17.5 min. ZOPAT was also easy to homogenise and operate due to its one-unit dosing system. The study attributes the success of ZOPAT to the presence of Zn, N, and K, which create electrostatic attraction with opposite charged particles, and the formation of dye-particle-dye with amide, hydroxyl, and carboxyl groups in ZOPAT, which remove colour, turbidity, COD, and SS. Overall, the study concludes that ZOPAT has significant potential for textile wastewater treatment.

Salinity Impacts on Floc Size and Growth Rate With and Without Natural Organic Matter

AbstractDue to the flocculation process, suspended mud aggregates carried by rivers to the coastal ocean are thought to undergo changes in size and shape in response to environmental drivers such as turbulence, sediment concentration, organic matter (OM), and salinity. Some have assumed that salt is necessary for floc formation, and that mud, therefore, reaches the estuary unflocculated. Yet mud flocs exist in freshwater systems long before the estuarine zone, likely due to the presence of OM acting as a floc‐promoting binder. Therefore, it is important to consider how salinity affects flocculation, if at all, in the presence of OM. Here, we used experiments to examine the flocculation of a natural mud with and without OM. Results showed that the rate of floc growth and equilibrium size both increase with salinity regardless of the presence or absence of OM. However, the response of both to salinity was stronger when OM was present. In deionized water, natural sediment with OM was seen to produce large flocs. However, the size distribution of the suspension tended to be bimodal. With the addition of salt, increasing amounts of unflocculated material became bound within flocs, producing a more unimodal size distribution. Here, the enhancing effects of salt were noticeable at even 0.5 ppt, and increases in salinity past 3–5 ppt only marginally increased the floc growth rate and final size. Data from the experiment were used to develop a salinity‐dependent model to account for changes in floc growth rate and equilibrium size.

Insight into the purification of algael water by a novel flocculant with enhanced branched nanochitosan structure

For improving inadequate nanostructural stability and promote algal removal efficiency, a novel nanochitosan-grafted flocculant (PAD-g-MNC) with an enhanced branched nanostructure and high molecular weight (MW) was fabricated via maleic anhydride acylation polymerization. Characterization results verified the successful synthesis of the flocculant and the formation of an irregular particle nanostructure. PAD-g-MNC exhibited superior algal and extracellular organic matter (EOM) removal and obtained the turbidity and chlorophyll-a removal rates of 93.46%–95.39% and 95.10%–97.31%, respectively, at the dosage of 4–5 mg L−1. The growth rate, strength factor, and recovery factor of algal flocs flocculated by PAD-g-MNC were 90.36, 0.63, and 0.27 (100 rpm), respectively, and were higher than other flocculants prepared through conventional methods. Results indicated that the high intrinsic viscosity and stability branched nanostructure promoted the formation of stable flocs and regeneration ability of flocs. MW distribution and three-dimensional fluorescence analyses revealed that the special structure of PAD-g-MNC was beneficial to the removal of tryptophan-like proteins in EOM. Strong adsorption–adhesion and bridging–netting effects of the nanostructure chain were the dominated mechanisms in the improvement of flocculation efficiency. This study provided theoretical and experimental guidance for the design of flocculants with superior performance and efficient algal water purification performance.

Floc formation and growth during coagulation removing humic acid: Effect of stirring condition

Number of studies have explored the mechanism of humic acid (HA) removal by coagulation, while studies on the formation and growth mechanism of HA-floc are still limited. In this study, a series of dynamically monitored experiments were carried out and floc characterization techniques were applied to investigate HA-floc growth mechanisms and properties under different stirring conditions. First, HA was removed in the early stages and varied insignificantly during floc growth, and the stirring condition did not affect the removal of HA. Moreover, HA hindered the effective collision, resulting in a slower floc growth rate and a lower fractal dimension. Although stirring condition did not markedly affect the HA removal performance, it had a remarkable effect on floc growth and structure. For example, gentle stirring resulted in larger floc d50 and pore size. Intense stirring accelerated the breakage or aging of flocs, resulting in a reduction in the final floc size at equilibrium. In particular, fast stirring in the early stage of coagulation advanced floc growth, but decreased the zeta potential and active sites of flocs, and reduced the capacity of the primary aggregates to grow into larger flocs. This study provides information on the floc formation and growth mechanism and the properties of flocs formed under different stirring conditions, which are helpful for optimizing the coagulation process on organic matter removal and guide the processes utilizing flocs.

Combined dual-size foam glass media filtration process with micro-flocculation for simultaneous removal of particulate and dissolved contaminants in urban road runoff

In this study, a combined media filtration process with micro-flocculation (CMF) was developed, to simultaneously treat particulate and dissolved contaminants in urban road runoff. Dual-size foam glass media with stone and sand layers were applied and the efficiency of road runoff treatment was investigated according to filtration and micro-flocculation under various experimental conditions (stone/sand layer ratio, linear velocity, and coagulant types). Moreover, the removal efficiencies of suspended solids (SS), phosphorus, organic carbon, and heavy metals (Zn, Cu, Pb, Cd) by CMF were evaluated. The removal rate of SS was maintained to be above 84.1% for 1 h filtration by the dual-size foam glass, regardless of increasing pressure. The removal of phosphorus by micro-flocculation was more suitable in alum than ferric due to a higher initial floc growth rate and an increased particle size. The performance of the CMF was significantly improved over media filtration only process (MF) in removing both particulate and dissolved contaminants. The removal efficiency of all particulate pollutants by CMF was found to be more than 90%, and notably, the dissolved phosphorus, which was mostly not removed by MF, was also removed by 97.4%. Meanwhile, the backwash efficiency of CMF was half that of MF. Physical removal mechanisms, such as internal diffusion, dominated MF, whereas chemical removal mechanisms, such as adsorption and surface precipitation, dominated CMF. These results show the potential of the CMF process for the treatment of urban road runoff and identify the removal mechanisms of the filtration process that use micro-flocculation with dual-size foam glass.

Application of Polyaluminum Chloride-Polyacrylamide as New Water Treatment Material for the Removal of Natural Organic Matter

Natural organic matter (NOM) is easily soluble in surface water and difficult to be removed thoroughly. In this paper, polyaluminum chloride-polyacrylamide (PAC-PAM), as a new water treatment material, was proposed to solve this problem by coagulation treatment. The performance, mechanism and kinetic process of NOM removal were investigated systematically. Results showed that the optimum dosage of PAC and PAM was 10 mg/L and 0.5 mg/L for NOM removal of Yellow River water. In this condition, NOM could be removed effectively due to positively charged PAM addition. The size, growth rate and recovery factor of flocs generated by PAC-PAM reached 419 μm, 34.9 μm/min and 0.48, respectively, while only 355 μm, 27.9 μm/min and 0.31 were obtained by PAC. Moreover, the adsorption and bridging effect of PAM assisted the formation of multi-branched flocs, which brought fast settle velocity and low turbidity of supernatant after coagulation.

Characteristics and mechanism of chitosan in flocculation for water coagulation in the Yellow River diversion reservoir

In this paper, water from the Yellow River reservoir was treated with Polyaluminum chloride (PAC) and a PAC/chitosan (CTS) composite to study the flocculation efficiency, changes in the flocculation characteristics, and the role played by CTS in the process of coagulation. The floc microstructure was analyzed by scanning electron microscopy, and the floc characteristics and fractal dimension were studied using a laser particle size analyzer. The results showed that addition of a small quantity of CTS could produce a relatively good coagulation effect, and the removal effect of each index increased by 8.7 %–46.83 % compared with that obtained with only PAC. However, as the dose increased, the effects on various indexes did not increase significantly. Under the same conditions, the growth rate and size of flocs formed with the composite coagulant containing CTS were better than those obtained with only PAC, with an increase in the floc size about 36.67 % with CTS. The floc regeneration capacity showed the opposite trend. It is likely that when long-chain bridging is dominant, the conditions are more conducive to rapid formation of structured and dense flocs. By contrast, when electrical neutralization plays a leading role, the flocs have better disintegration and regeneration abilities.

Laboratory study of the properties of frazil ice particles and flocs in water of different salinities

Abstract. Measurements of the size and shape of frazil ice particles and flocs in saline water and of frazil ice flocs in freshwater are limited. This study consisted of a series of laboratory experiments producing frazil ice at salinities of 0 ‰, 15 ‰, 25 ‰ and 35 ‰ to address this lack of data. The experiments were conducted in a large tank in a cold room with bottom-mounted propellers to create turbulence. A high-resolution camera system was used to capture images of frazil ice particles and flocs passing through cross-polarizing lenses. The high-resolution images of the frazil ice were processed using a computer algorithm to differentiate particles from flocs and determine key properties including size, concentration and volume. The size and volume distributions of particles and flocs at all four salinities were found to fit log-normal distributions closely. The concentration, mean size, and standard deviation of flocs and particles were assessed at different times during the supercooling process to determine how these properties evolve with time. Comparisons were made to determine the effect of salinity on the properties of frazil ice particles and flocs. The overall mean size of frazil ice particles in saline water and freshwater was found to range between 0.52 and 0.45 mm, with particles sizes in freshwater ∼13 % larger than in saline water. However, qualitative observations showed that frazil ice particles in saline water tend to be more irregularly shaped. The overall mean size of flocs in freshwater was 2.57 mm compared to a mean size of 1.47 mm for flocs in saline water. The average growth rate of frazil particles was found to be 0.174, 0.070, 0.033, and 0.024 mm min−1 and the average floc growth rate was 0.408, 0.118, 0.089, and 0.072 mm min−1 for the 0 ‰, 15 ‰, 25 ‰, and 35 ‰, respectively. Estimates for the porosity of frazil ice flocs were made by equating the estimated volume of ice produced based on thermodynamic conditions to the estimated volume of ice determined from the digital images. The estimated porosities of frazil ice flocs were determined to be 0.86, 0.82, 0.8 and 0.75 for 0 ‰, 15 ‰, 25 ‰ and 35 ‰ saline water, respectively.

Effects of powdered activated carbon on the coagulation-flocculation process in humic acid and humic acid-kaolin water treatment

The addition of powdered activated carbon (PAC) to remove micropollutants is a commonly used technology to improve drinking water quality. However, the effects of PAC dosing strategy on the coagulation-flocculation process of water treatment have not been well understood, especially for water with low amounts of inorganic particles. Therefore, the current research aimed to comprehensively study the effects of simultaneous addition of PAC and aluminum sulfate (AS) coagulants (denoted as PAC-AS) or adding PAC 2 h before coagulation (denoted as PAC2h-AS) on the coagulation behavior in humic acid (HA) and HA-kaolin water treatment. The results showed that the floc size, growth rate, breakage factor, and fractal dimension were all enhanced by PAC-AS and PAC2h-AS for HA but not for HA-kaolin water treatment. In HA water treatment, PAC-AS reached a larger floc size and faster growth rate, while PAC2h-AS achieved a larger floc breakage factor and fractal dimension value. For PAC2h-AS, the pre-adsorption of HA onto PAC would lower the initial particle concentration and reduce the collision probability during HA water coagulation process; thus, the DOC removal efficiency, floc size, and growth rate of PAC2h-AS were relatively smaller than those of PAC-AS. For the floc strength and floc fractal dimension, the pre-adsorption of HA onto PAC contributed to formation of stronger inter-particle bonds; thus, stronger and more compact flocs were formed by PAC2h-AS compared with those of PAC-AS. The addition of PAC had a smaller impact on the floc properties in HA-kaolin water treatment owing to its higher initial particle concentration.

Enhanced Production of in Situ Keggin Al137+ Polymer by a Combined Fe-Al Coagulation Process for the Treatment of High Alkalinity Water

Treatment of high alkalinity water by coagulation is one of the challenges for drinking water treatment. The solution of acidifying the raw water or adding more coagulants would inevitably increase the corrosive tendency and treatment costs. In this study, a combined Fe-Al coagulation, during which a small amount of Fe was introduced prior to Al, promoted the coagulation efficiency of Al salts significantly. In contrast to the individual Al process, the combined Fe-Al coagulation accelerated the floc growth rate with the turbidity removal increased from 46% to 73% at the Fe:Al mole ratio of 1:10 and time interval of 10 s, and better tolerated the high basicity. The Keggin Al137+ polymer of the combined process was confirmed by the surface-enhanced Raman spectroscopy, X-ray photoelectron spectra, and 27Al nuclear magnetic resonance analyses, and its enhanced generation induced by the Fe addition was investigated by the Ferron assay. The favored local pH at the colloid-water interface governed by the hydrol...

The influence of particle size and concentration combined with pH on coagulation mechanisms

In order to evaluate the influence of particle size and particle concentration on the coagulation process, two kinds of particle suspensions, nanoparticles and microparticles, were employed to investigate the effect of particle size on coagulation mechanisms with varying coagulation parameters. Results showed that it is easier for nanoparticles to cause self-aggregation because of Brownian motion, while interception and sedimentation are the mainly physical processes affecting particle transport for microparticles, so they are more stable and disperse more easily. The particle size distribution and particle concentration had distinct influence on the coagulation mechanisms. Under neutral conditions, as the amount of coagulant increased, the coagulation mechanism for nanoparticles changed from charge neutralization to sweep flocculation and the nanoparticles became destabilized, re-stabilized and again destabilized. For microparticles, although the coagulation mechanism was the same as that of nanoparticles, the increased rate of aluminum hydroxide precipitation exceeded the adsorption of incipiently formed soluble alum species, resulting in the disappearance of the re-stabilization zone. Under acidic conditions, Brownian motion dominates for nanoparticles at low particle concentrations, while sweep flocculation is predominant at high particle concentrations. As for microparticles, charge neutralization and sweep flocculation are the mechanisms for low and high particle concentrations respectively. Under alkaline condition, although the mechanisms for both nano- and microparticles are the same, the morphology of flocs and the kinetics of floc formation are different. At low particle concentrations, nanoparticles have larger growth rate and final size of flocs, while at high particle concentrations, nanoparticles have higher fractal dimension and recovery factors.

Coagulation Behavior and Floc Properties of Dosing Different Alkaline Neutralizers into the Fenton Oxidation Effluent

Neutralization is the necessary operation to ensure the Fenton effluent pH. In situ coagulation can be induced during neutralization. In this study, three types of alkaline neutralizers (Ca(OH)2, NaOH, and Ca(OH)2 + NaOH) were added into the Fenton oxidized PSE to control the effluent pH of 6 to 9. The coagulation behavior, floc structure, and properties were investigated. The results indicated that the coagulation with the adding of three neutralizers can remove 9.68 to 24.02% of the TOC. Ca(OH)2 exhibited the highest TOC removal efficiency at the dosage of 0.4 g/L. Charge neutralization ability was in the following order: Ca(OH)2 > Ca(OH)2 + NaOH > NaOH. Ca(OH)2 and Ca(OH)2 + NaOH showed the increase of floc growth rate with the increase of agent dosage, especially for Ca(OH)2 + NaOH. Moreover, Df of NaOH flocs was higher than that of Ca(OH)2 and Ca(OH)2 + NaOH, indicating the floc formed by NaOH was more compact than that of Ca(OH)2. The main coagulation process of three neutralizers was different, and it was also affected by the agent dosage (or pH). When the dosage was 0.35 g/L (pH 6–7.5), the complexation, adsorption, and bridging were the predominant processes while charge neutralization gradually became the main coagulation process for Ca(OH)2 and Ca(OH)2 + NaOH with the increase of dosage (pH 7.5–9).

The role of mixing hydrodynamics on floc growth in unbaffled square stirred-tank reactors for flocculation

This study focuses on the effect of mixing hydrodynamics, generated in unbaffled square stirred tanks with different liquid-level heights (H), on floc growth during flocculation over the same shear-rate range (Gave = 10–70 s−1) by using an in-situ recognition system for floc morphology. The hydrodynamic environments under each combination of H and Gave were characterized by calculated circulation time (tc) and impeller tip speed (Nd). It was found that the temporal evolution of floc size appeared to be sensitive to the value of H at a given Gave, and with increasing Gave, greater difference occurred at the same flocculation moments for different H-value cases. Also, under a fixed Gave-value condition, the H-value effect on floc size evolution at steady state of flocculation was shown to largely depend upon the predominant growth mechanism(s). An appropriate liquid-level height should be required to bring about an optimal combination of tc and Nd, thereby maximizing floc growth rate under both aggregation-dominated and breakage-dominated circumstances for enhancing floc formation and subsequent particle removal efficiency. The present study may provide useful insights into the design and operation of stirred-tank reactors for flocculation.

Evaluation of cationic polyacrylamide-based hybrid coagulation for the removal of dissolved organic nitrogen.

Dissolved organic nitrogen (DON) is an important component of aquatic environment of which amount impacts water quality. Thus, removal of DON has attracted wide attention. At present, it is difficult for common coagulation to remove DON from the aquatic environment. The cationic polymers can help to improve the removal efficiency of DON to some extent, but the underlying mechanism of the ascension is not clear. In order to grasp its removal behavior and further improve the removal efficiency of DON in the future, we evaluated the effect of a hybridized coagulant of polyacrylamide with iron-based coagulant on removal of aquatic DON. A higher floc growth rate (119.82μm/min) and recovery factors (26.96) were found in the hybrid coagulation. The parameters affecting the DON and the dissolved organic carbon (DOC) included the molar ratio of Zn to Fe (nZn/nFe), CPAM content, and molar ratio of OH to Fe (nOH/nFe): nZn/nFe had a larger influence in DON removal than CPAM content; CPAM had a larger influence in the DOC removal; nOH/nFe played a moderate effect between CPAM and nZn/nFe. Mutual effect of hybrid coagulants indicated the colloidal species to be helpful in enhancing DOC and DON removal. Other parameters affecting coagulation performance included the pH: the estimated maximum DON removal efficiency occurred at pH 6, DOC removal efficiency at pH 8. The above results found in this study showed that DON removal was affected by the ingredient and the species composition of the hybrid coagulant, and the water environmental parameter. The enhanced efficiency of DON removal in the presence of CPAM was mainly attributed to the increased adsorption-bridging and sweep-floc.

In situ polymer flocculation and growth in Taylor-Couette flows.

Flocculation of small particulates suspended in solution is a key process in many industries, including drinking water treatment. The particles are aggregated during mixing to form larger aggregates, known as flocs, through use of a polyelectrolyte flocculant. The flocculation of these particulates in water treatment, however, are subject to a wide spatial variation of hydrodynamic flow states, which has consequences for floc size, growth rate, and microstructure. Floc assembly dynamics are explored here using a commercially available cationic polyacrylamide, commonly used in water treatment, and anisotropic Na-bentonite clay particles under a variety of hydrodynamic mixing conditions. A Taylor-Couette cell with the unique ability to radially inject fluid into the rotating annulus was used to study how specific hydrodynamic flow fields affect assembly and structure of these materials during the flocculation process. Faster floc growth rates and decreased floc fractal dimensions were observed for higher order flow states, indicating improved mass transfer of the polymer flocculant and breakage at the edges of the flocs (shear rounding), respectively. This work sheds more light on the complexities of polymer-induced flocculation, towards improving dosing and efficiency of large-scale operations.

Inhibition of disinfection by-product formation in silver nanoparticle-humic acid water treatment

Abstract Health risk of disinfection by-products (DBPs) makes the removal of trihalomethanes (THMs) precursors a great concern in water treatment. This study investigated the THMs precursors removal by coagulation with four coagulants, namely TiCl 4 , polymerized titanium chloride (PTC), Al 2 (SO 4 ) 3 , polymerized aluminum chloride (PAC), in silver nanoparticle-humic acid (AgNPs-HA) water treatment. Flocs formed during coagulation process were characterized using a laser diffraction particle-sizing device, and the residual dissolved organic matter (DOM) in coagulated water was characterized using three-dimensional Excitation and emission matrix (3DEEM) fluorescence spectroscopy. Results showed the reduction of THMs by a large margin through coagulation by the four coagulants, and CHCl 3 and CHBrCl 2 were observed as main species. Compared with conventional Al 2 (SO 4 ) 3 and PAC, TiC 4 and PTC achieved efficient AgNPs removal and were superior in terms of DOM removal with improved floc characteristics in terms of floc growth rate and floc size. Analysis of 3DEEM results suggested the fluorescent substance removal ability of TiCl 4 > PTC > Al 2 (SO 4 ) 3 > PAC, and the predominant fulvic acid-like DOM was removed to the largest extent through coagulation. Besides, anatase structured TiO 2 with efficient photocatalytic performance was finally recovered from TiCl 4 and PTC coagulated sludge. The atomic percentage of Ag-doped TiO 2 was TiO 1.82 Cl 0.25 Na 0.29 Ag 0.14 .

Stability, morphological transformation and flocculability investigation of planar tridecameric Al 13 (OH) 24 (H 2 O) 24 15+

Abstract Though great efforts have devoted to prepare planar Al13 [Al13(OH)24(H2O)2415+, M-Al13], the lack of knowledge of its stability and hydrolysis behavior in aqueous solution limits its practical application as coagulant. In this study, the stability, morphological transformation and coagulation property of M-Al13 were thoroughly investigated. The 27Al-NMR spectra revealed temperature-dependent morphological transformation from M-Al13 to K-Al13 in aqueous solution. This transformation was completely inhabited below 5 °C, but was accelerated with increased temperature from 5 to 70 °C. Moreover, higher temperature and longer aging time led to further transformation of K-Al13 to the aluminum species with higher degree of polymerization such as Al30. Thus, low temperature was favorable for the morphological stability of M-Al13. Due to the maintenance of M-Al13 structure, all as-prepared M-Al13 crystal, M-Al13 solution (0 °C) and freeze dried M-Al13 showed excellent and comparable flocculation property in the terms of floc growth rate, floc size and floc strength. Interestingly, the flocculability dramatically decreased after M-Al13 solution aged at 25 °C or 40 °C for 120 min with 29% and 62% of M-Al13 transformed to K-Al13, respectively. These results implied that M-Al13 was an important flocculant with better performance than the well-known and efficient flocculant K-Al13. Our study about the stability and hydrolysis behavior of M-Al13 might prompt its application as a highly efficient flocculent for water purification.

Adsorption Neutralization Model and Floc Growth Kinetics Properties of Aluminum Coagulants Based on Sips and Boltzmann Equations.

Single-molecule aluminum salt AlCl3, medium polymerized polyaluminum chloride (PAC), and high polymerized polyaluminum chloride (HPAC) were prepared in a laboratory. The characteristics and coagulation properties of these prepared aluminum salts were investigated. The Langmuir, Freundlich, and Sips adsorption isotherms were first used to describe the adsorption neutralization process in coagulation, and the Boltzmann equation was used to fit the reaction kinetics of floc growth in flocculation. It was novel to find that the experimental data fitted well with the Sips and Boltzmann equation, and the significance of parameters in the equations was discussed simultaneously. Through the Sips equation, the adsorption neutralization reaction was proved to be spontaneous and the adsorption neutralization capacity was HPAC > PAC > AlCl3. Sips equation also indicated that the zeta potential of water samples would reach a limit with the increase of coagulant dosage, and the equilibrium zeta potential values were 30.25, 30.23, and 27.25 mV for AlCl3, PAC, and HPAC, respectively. The lower equilibrium zeta potential value of HPAC might be the reason why the water sample was not easy to achieve restabilization at a high coagulant dosage. Through the Boltzmann equation modeling, the maximum average floc size formed by AlCl3, PAC, and HPAC were 196.0, 188.0, and 203.6 μm, respectively, and the halfway time of reactions were 31.23, 17.08, and 9.55 min, respectively. The HPAC showed the strongest floc formation ability and the fastest floc growth rate in the flocculation process, which might be caused by the stronger adsorption and bridging functions of Alb and Alc contained in HPAC.

Coagulation behavior and floc characteristics of a novel composite poly-ferric aluminum chloride-polydimethyl diallylammonium chloride coagulant with different OH/(Fe3+ + Al3+) molar ratios.

In this paper, flocculating performance and mechanisms of a new composite coagulant, poly-ferric aluminum chloride-polydimethyl diallylammonium chloride (PFAC-PD) with different OH-/(Fe3+ + Al3+) molar ratios, were investigated for humic acid (HA)-kaolin synthetic wastewater treatment. The impact of OH-/(Fe3+ + Al3+) molar ratios on the removal efficiencies of turbidity and dissolved organic carbon, specific UV absorbance, coagulation mechanisms and dynamics was explored during the coagulation process using composite coagulants. The coagulation experimental results revealed that the composite coagulants with lower OH-/(Fe3+ + Al3+) molar ratio exhibited better coagulation efficiency. When OH-/(Fe3+ + Al3+) molar ratio of the composite coagulant was 1.5, adsorption-bridging played a dominant role in coagulating HA-kaolin synthetic wastewater. The floc growth rate and floc size, increased with increasing OH-/(Fe3+ + Al3+) molar ratio and the highest peak height of the size distribution was obtained by PFAC-PD with OH-/(Fe3+ + Al3+) = 1.5. Also, the composite coagulants with higher OH-/(Fe3+ + Al3+) molar ratio formed more compact flocs, as reflected by the higher fractal dimension value. The flocs coagulated by PFAC-PD with basicity value of 1.0 gave strong strength and good recoverability.

Polytitanium sulfate (PTS): Coagulation application and Ti species detection

Interest in the development of inorganic polymerized coagulants is growing; however, there are only limited studies on the synthesis of polytitanium coagulants, which are expected to exhibit improved coagulation efficiency with better floc properties. This study presents the synthesis of polytitanium sulfate (PTS) for potential application in water purification, followed by characterization of PTS flocs and titanium species detection. Stable PTS solutions were successfully synthesized and standard jar tests were conducted to evaluate their coagulation efficiency. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) speciation analysis revealed that a variety of mononuclear and polynuclear complexes were formed in PTS solution, indicating the polymeric nature of the synthesized coagulant. Floc characteristics were studied through on-line monitoring of floc size using a laser diffraction particle size analyzer. Results showed that PTS had a comparable or in some cases even higher organic matter and particulate removal efficiency than Ti(SO4)2. The effluent pH after PTS coagulation significantly improved toward desirable values closer to neutral pH. Properties of flocs formed by PTS were significantly improved in terms of floc size, growth rate and structure. This study showed that PTS could be an efficient and promising coagulant for water purification, with the additional benefit that its coagulated sludge can be used to recover valuable TiO2 nanoparticles for various commercial applications.