No abstract

Recently, more attentions have been paid to natural polymer-based flocculants in water treatment, since they are believed to be low-cost, nontoxic, and environmentally friendly materials. In this work, strong cationic chitosan-based graft copolymer flocculants (3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CTA) modified chitosan-graft-polyacrylamide, denoted as chitosan-CTA-g-PAM) have been prepared, and their flocculating properties were studied systematically, both at the laboratory scale and at the pilot scale. In laboratory scale, a kaolin suspension was employed as synthetic wastewater. The effects of dosage, temperature, and original turbidity of untreated wastewater were investigated, respectively. Moreover, in pilot scale, the raw water from the Zhenjiang part of the Yangtse River in China was used as wastewater. The influences of three external factorsdosage, sedimentation time, and mechanical mixing rate-on the flocculating performances have been studied by orthogonal testing, respectively. The experimental results in pilot scale were fairly consistent with those from the beaker experiment in laboratory scale. In comparison with polyferric sulfate, which is the flocculant currently used by the Zhenjiang Water Supply Company, chitosan-CTA-g-PAM showed better flocculating properties. Meanwhile, the effect of the degree of substitution of CTA on the flocculating properties has been also studied, both at the laboratory scale and at the pilot scale. It was indicated that chitosan-CTA-g-PAM with higher cationic degree had better flocculating performances, which was also confirmed by the flocculation kinetics analysis. Furthermore, the flocculation mechanisms of chitosan-CTA-g-PAM have been discussed in detail. Above all, the flocculating experiments in laboratory and pilot scales both indicated that chitosan-CTA-g-PAM showed good flocculating performances in water treatment.

A series of chitosan-graft-polyacrylamide copolymers have been prepared as flocculants for waste water treatment. The results indicated that the grafting ratio was one of the key factors for the flocculating effects. The copolymers with various grafting ratios showed different flocculating properties. To observe every detail of this effect, the specific refractive index increment measurement (SRIIM) method was used to determine the grafting ratio at the beginning of this study. Interestingly, it was found that as the grafting ratio increased, the flocculating effect increased until it reached its maximum point. At that point, it decreased. This result was discussed in terms of the cooperative effects of the charge neutralization and bridging flocculating mechanisms. A structure model of chitosan-g-polyacrylamide copolymer flocculants has been proposed.

In this study, the flocculating properties of chitosan-graft-polyacrylamide (PAM) copolymer flocculants have been investigated in pilot scale, and the raw water from Zhenjiang part of Yangtse river in China was used as simulated waste water. The influences of dose, mechanical mixing rate, and sedimentation time to the flocculating effects have been investigated in different seasons: summer and winter, respectively. The optimal experimental conditions have been studied by orthogonal test. In addition, the structure effects of the flocculants: the grafting ratio, on the flocculating properties have been also investigated in pilot scale, which results were fully consistent to those from the beaker experiment in laboratory scale using kaolin suspension as simulated waste water. Compared to poly ferric sulfate, current used flocculants in Jinxi Water Factory, chitosan-g-PAM copolymer flocculants showed better flocculating properties, which was ascribed to the cooperative effects of the charge neutralization and bridging flocculating mechanisms of polymer flocculants. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci

No abstract