Carbohydrates are the main varieties of natural polymer coagulant class (glucan), Chitosan, chitin, microbial coagulants such three categories, usually using the extraction of organic polymeric material in agricultural and sideline products produced, cheap, easily biodegradable, but smaller charge density, low molecular weight, and prone to degradation and loss of coagulation activity, it is not widely used.
Based on cheap, nontoxic, biodegradable cationic starch in starch as raw material, treatment of industrial waste water is an excellent polymer coagulant and anion exchangers. Below 0.3 degree of substitution of cationic starch on decolorization of printing and dyeing wastewater with high efficiency, low consumption, low cost and no secondary pollution and so on. With such  selection of n-epoxypropyl trimethyl ammonium chloride (GTA) as a cationic reagent, based on 6% aqueous solution of LiOH catalyst control temperature of 70 ° c, the reaction time of 2 h, reaction system water content 24.6%, replaced by dry preparation for 0.5 of cross-linking cationic starch (CCS), the effect is about 90%. Li xuxiang  with (NH4) 2SO4 initiator, starch and acrylonitrile graft copolymerization modified starch flocculant produced, used in the treatment of printing and dyeing wastewater and chroma removal rate is 91 per cent.