Organic polyelectrolytes in water treatment.

Chitin and its deacetylated derivative chitosan are natural polymers composed of randomly distributed � -(1-4)- linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). Chitin is insoluble in aqueous media while chitosan is soluble in acidic conditions due to the free protonable amino groups present in the D-glucosamine units. Due to their natural origin, both chitin and chitosan can not be defined as a unique chemical structure but as a fam- ily of polymers which present a high variability in their chemical and physical properties. This variability is related not only to the origin of the samples but also to their method of preparation. Chitin and chitosan are used in fields as different as food, biomedicine and agriculture, among others. The success of chitin and chitosan in each of these specific applica- tions is directly related to deep research into their physicochemical properties. In recent years, several reviews covering different aspects of the applications of chitin and chitosan have been published. However, these reviews have not taken into account the key role of the physicochemical properties of chitin and chitosan in their possible applications. The aim of this review is to highlight the relationship between the physicochemical properties of the polymers and their behaviour. A functional characterization of chitin and chitosan regarding some biological properties and some specific applications (drug delivery, tissue engineering, functional food, food preservative, biocatalyst immobilization, wastewater treatment, molecular imprinting and metal nanocomposites) is presented. The molecular mechanism of the biological properties such as biocompatibility, mucoadhesion, permeation enhancing effect, anticholesterolemic, and antimicrobial has been up- dated.

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Functional Characterization of Chitin and Chitosan

Chitosan for coagulation/flocculation processes. An eco-friendly approach.

A review on application of flocculants in wastewater treatment

A review on chitosan-based flocculants and their applications in water treatment

Chitosan has unique properties among biopolymers, especially due to the presence of primary amino groups. Chitosan has been used for the chelation of metal ions in near‐neutral solution, the complexation of anions in acidic solution (cationic properties due to amine protonation), the coagulation of negatively charged contaminants under acidic conditions, and for precipitative flocculation at pH above the pKa of chitosan. The coagulation and flocculation properties can be used to treat particulate suspensions (organic or inorganic) and also to treat dissolved organic materials (including dyes and humic acid). This paper will give an overview of the principal results obtained in the treatment of various suspensions and solutions: (a) bentonite suspensions; (b) organic suspensions; (c) anionic dye solutions; and (d) humic acid solutions. Stoichiometry and charge restabilization were determined for the coagulation of humic acid, kaolin, and organic dyes with chitosan, indicating charge neutralization...

A Review of the Use of Chitosan for the Removal of Particulate and Dissolved Contaminants

Influence of chitosan characteristics on the coagulation and the flocculation of bentonite suspensions

Chitosan dissolved in acetic or hydrochloric acid was used for the coagulation and the flocculation of bentonite colloids. The influence of pH was investigated and the double effect of the biopolymer was identified. Experiments were performed at different polymer concentrations and at different pHs with simulated suspension (prepared with different amounts of bentonite). At pH 5 (acidic region), the protonation of amine groups led to coagulation effect and very low amounts of polymer were required to achieve a fast and efficient decantation of colloids; at pH close to neutral, a different mechanism was involved in the flocculating effect of the polymer chain (larger amounts of polymer were usually required). The effect of the characteristics of the polymer, i.e., degree of deacetylation, and polymer weight (related to polymer viscosity) was also investigated in order to optimize the selection of the biopolymer for targeted experimental concentrations.

Chitosan for the Coagulation and Flocculation of Mineral Colloids

A coagulation/flocculation process using a selection of biopolymers (chitosan and tannin) was used to treat an ink-containing effluent generated in the processing of packaging. The efficiency of the process was investigated in terms of the influence of pH, coagulant and flocculant concentrations, as well as chitosan characteristics (especially the molecular weight). The process was particularly efficient under acidic solutions: the amount of coagulant and flocculant to be used were significantly reduced by limiting the pH to 5. Optimum conditions for colour abatement (measured at 528 nm) were obtained at pH 5 using the most viscous chitosan (highest molecular weight) at a concentration close to 20 mg·l-1 and a concentration of tannin close to 70-100 mg·l-1.. Water SA Vol.31 (3) 2005: pp.369-376

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Treatment of ink-containing wastewater by coagulation / flocculation using biopolymers

Several samples of chitosan with different degrees of deacetylation and of different molecular weights were tested for the coagulation–flocculation of organic suspensions. Organic suspensions were prepared by mixing mushroom powder with tap water. Experiments were carried out at pH 5, pH 7, and pH 9. Because decreasing the pH reduced the amount of chitosan required to reach the required turbidity, at pH 9, a high concentration of chitosan was required to achieve the required treatment levels, whereas the difference was less significant between pH 7 and pH 5 (the required concentration of chitosan was halved). Though viscosity, correlated to the molecular weight of chitosan, affected treatment performance, its influence on the efficiency of coagulation–flocculation could be substantially reduced by slightly increasing the concentration of the polymer. This is of importance in the processing of industrial effluents: the aging of a chitosan solution, which may cause partial depolymerization, and loss of viscosity, will have a limited impact on process efficiency. The degree of deacetylation also has a limited effect on treatment performance, especially when the degree of deacetylation exceeds 90%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2070–2079, 2005

Maurice Van Vooren

Papers

A Review of the Use of Chitosan for the Removal of Particulate and Dissolved Contaminants

Influence of chitosan characteristics on the coagulation and the flocculation of bentonite suspensions

Chitosan for the Coagulation and Flocculation of Mineral Colloids

Treatment of ink-containing wastewater by coagulation / flocculation using biopolymers

Influence of chitosan characteristics on coagulation and flocculation of organic suspensions