Plant polysaccharides as a new source for coagulant-flocculant aids and surfactants

Polysaccharides are polymeric carbohydrate structures, formed of repeating units (either mono- or disaccharides) joined together by O-glycosidic bonds. Virtually, polysaccharides can be found in any vegetal, specially forming structural complexes. Non-starch water soluble polysaccharides are usually isolated by dissolving-purificationalcohol precipitation process. Lipids can be removed by solvent extraction of raw materials. Protein can be removed by enzyme digestion, while insoluble fiber can be removed by centrifugation of polysaccharide solutions. Finally, it can be said that most of purification cost comes from alcohol consumption. Plant polysaccharides have been employed in a wide range of applications. Very traditional gums, such as Arabic, karaya and tragacanth gums, which in turn are exudates gums, are known from ancient times. Their recent applications range from food (beverages bases, chewing gums, confectionary and frostings, dairy products analogs, fats and oils, gelatins, puddings and fillings, hard candy, etc.) to non-food applications (pharmaceutical industry, suspending agents, etching and plating solutions, foam stabilizers, dispersant in paint and insecticidal emulsions, etc). More specifically, these polysaccharides are very interesting because of their emulsion properties such as surface tension, emulsion capacity and emulsion stability, as well as their rheological properties. Besides these applications nowadays the use of these natural gums in the treatment of municipal and industrial wastewaters has been reported. These products act as coagulant-flocculants, substituting Fe and Al salts+ synthetic polymers in the treatment of contaminated waters. Sludges and waters produced in the treatment contain fewer metals and in the case of the sludges, they result more biodegradable. On the other hand, some vegetal gums have been employed as surfactantsemulsifiers in the field of remediation of contaminated soils. Some of these products have been employed successfully in the washing of soils contaminated with petroleum hydrocarbons, different metals, pharmaceutical products or pesticides. They are used in smaller quantities than their counterpart (i.e, synthetic surfactants). An additional purpose of the use of vegetal products is that wastewater generated are biotreated more easily that the wastewaters generated when using synthetic products. A second application in the treatment of contaminated soils, is its use in small quantities for the biodegradation of products present in contaminated soils, only as an aid, to enhance the desorption of organic products and thus, the microorganisms can use more efficiently the organic compounds as carbon or energy sources. The benefit of using natural products is the concern of leaving non-degraded products in soils which could be hardly biodegraded in long periods. This chapter describes the polysaccharides, emphasizing in those of vegetal origin. Also, a description of some of the functional properties of the vegetal products is made. Finally, the main applications of natural products as coagulant-flocculants or surfactants are discussed.