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This is the first attempt to use cationic polyacrylamide (PAM) as coagulant aid with titanium tetrachloride (TiCl4) to improve the coagulation performance and floc properties. Coagulation-flocculation treatment was applied to simulated water (with fulvic acid (FA) as model organic matter) for both coagulation behavior investigation and floc characterization. The effect of PAM on floc reformation properties after cyclic breakage/regrowth was also investigated. Ultrafiltration experiments were performed to investigate the influence of PAM aided TiCl4 coagulation on the membrane fouling. The results showed that organic removal was enhanced by PAM addition at low TiCl4 doses. Floc growth rate and floc size were significantly affected by dosing sequence. TiCl4-PAM significantly improved the floc strength factors (Sf) and recovery factors (Rf). The dosing sequence of TiCl4 and PAM significantly influenced the floc structure. Characterization of the flocculated sludge indicated that TiO2 with anatase structure and high photocatalytic activity could be obtained from the TiCl4-PAM flocculated sludge., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Characteristics of flocs formed by charge neutralization and sweep coagulation using titanium tetrachloride (TiCl(4)) were investigated with humic acid-kaolin suspension by continuous optical monitoring. This paper focused on the regrowth ability of broken flocs after addition of second TiCl(4) dose. Variation of floc size and the fractal dimension of flocs versus second TiCl(4) dose after regrowth were investigated. Second TiCl(4) dose was added during the floc breakage period, and addition time of second TiCl(4) dose was also investigated. The results showed that, when coagulated by charge neutralization at pH 6, an appropriate second TiCl(4) dose improved regrowth ability of broken flocs at low initial TiCl(4) doses. While for high initial TiCl(4) doses, second TiCl(4) dose lowered floc re-growth ability. When coagulated by sweep coagulation at pH 10, second TiCl(4) dose made regrown flocs larger than those without second TiCl(4) dose. Floc structure analysis showed that it was determined by not only the fractal dimension of flocs, but also the chemical characteristics of floc surface. Addition time of second TiCl(4) dose had a great effect on floc regrowth ability, suggesting that the broken flocs had better regrowth when second TiCl(4) dose was added at the end of the breakage period., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The growth, breakage and regrowth nature of flocs formed by Titanium tetrachloride (TiCl(4)) and polyaluminum chloride (PACl) was comparatively evaluated with surface water treatment. A series of jar experiments were conducted to investigate the impacts of different operating parameters such as shear force, solution pH and a breakage period on floc strength and re-aggregation potential. Results indicated that the responses of flocs to different operating parameters depend on the coagulant used. The ability of floc to resist breakage decreased with the increase of shear force and breakage period. Floc strength properties were also measured in response to increasing shear force, with the results suggesting that the order of floc strength was TiCl(4)>PACl. Floc regrowth of the two coagulants after exposure to high shear was limited, and flocs formed by TiCl(4) displayed weaker recoverability. The flocs generated in acid conditions were more recoverable than those generated in alkaline conditions no matter which coagulant was used., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The floc strength and regrowth properties of three polyferric-cationic polymer dual-coagulants were comparatively evaluated using surface water sample. The first dual-coagulant PFC-PD was prepared by premixing of polyferric chloride (PFC) and polydiallyldimethylammonium (PDADMAC) before dosing. The other two, PFCF (PFC dosed firstly) and PDF (PDADMAC dosed firstly), were achieved by dosing PFC and PDADMAC in different order. Floc strength properties were measured in response to increasing shear levels in the long period and high shear level in the short or long period. For the given optimum dose (3.0 mg L(-1)) and water pH (6.5) condition, the order of floc strength was PFCF>PDF>PFC-PD. The dual-coagulant which gave stronger flocs also gave a lower absolute value of zeta potential. The floc regrowth properties of all three dual-coagulants after short and long period high shear level were also investigated. The floc recoverability was in the following order: PFCF>PFC-PD>PDF., ((c) 2009 Elsevier B.V. All rights reserved.)

A series of composite flocculants PFC-PD with different basicity (B) of polyferric chloride (PFC), different weight percentage (w(P)) and intrinsic viscosity (eta) of polydimethyl diallylammonium chloride (PDMDAAC) were prepared by prepolymerization. The turbidity, dissolved organic carbon (DOC) and specific ultraviolet absorbance (SUVA) removal efficiency as well as flocculation mechanism of PFC-PD were compared with that of PFC, PDMDAAC and successive addition of PFC and PDMDAAC in treating high DOC and high alkalinity surface water by jar tests. The effect of B, w(P) and eta on coagulation efficiency and mechanisms were also studied. The experimental results showed that PFC-PD was more efficient and more applicable for turbidity, DOC and SUVA removal than PFC, PDMDAAC and successive addition of PFC and PDMDAAC. Further, the water pH was slightly depressed by PFC-PD. Coagulation efficiency of PFC-PD was improved at lower B, larger w(P) and larger eta. Charge neutralization was dominant mechanism of PFC-PD.

Polyamine flocculants were synthesized by the polycondensation of dimethylamine and epichlorohydrin, in which organic amines, e.g. 1,2-diaminoethane, were used as modifying agents. Different products were obtained by varying the reaction parameters, such as the molar ratio of epichlorohydrin to dimethylamine, the amount of 1,2-diaminoethane and reaction temperature. The polyamine flocculants were characterized by transmission electron microscope (TEM). Their flocculation performance was evaluated with simulated dye liquor and actual printing and dyeing wastewater. The behavior of the flocculants was compared with that of inorganic coagulant, polyaluminum chloride (PAC). The experimental results show that polyamine with the highest viscosity and cationicity could be prepared under following conditions: an epichlorohydrin to dimethylamine molar ratio of 1.5, a reaction temperature of 70 degrees C, a 3% content of 1,2-diaminoethane in the total reaction monomers and a reaction time of 7h. Polyamine polymers can, as flocculants for treating simulated and actual dye wastewater, remove color and COD efficiently. The rate of color removal from reactive red liquor, reactive blue liquor and reductive yellow liquor reached as high as 96%, 97% and 96%, respectively. The highest efficiency of color removal and COD removal from polyamine for treating dye wastewater was 90% and 89%, respectively.

Fly ash modification by polydimethydiallylammonium chloride (PDMDAAC) in laboratory scale was explored in this work and the adsorption performance of modified fly ash and its application in dyeing wastewater treatment were also studied. The key factors (concentration and temperature) for PDMDAAC to affect the adsorption properties of fly ash (FA) were revealed using the orthogonal test with four factors. The results indicated that the adsorption magnitude of fly ash to PDMDAAC increased due to its favorable specific surface causing the change of the surface charge nature. Hence, adsorption performance of modified fly ash on organic molecules and its ion exchange capacity are strengthened. The maximum color removal efficiency was obtained as 88.2% by modified fly ash with 2.0 g/100 mL dosage in dyeing wastewater, which is much higher than 12.5% color removal efficiency by raw fly ash with the same dosage. And, the used modified fly ash could be used for cement production as additive agent. The intensity of cement produced with 15% the modified fly ash in weight reached the Chinese Cement Standard (GB/T17671-1999), blazing a promising novel way in fly ash utilization.