The Study On Modified Starch Applied In Water Treatment

In order to wipe off the suspended pollutants and heavy metal ions in wasterwater, a great number of organic and inorganic flocculants have been synthesized. However,most of them are expensive, micro-toxic and the residual sludge is hard to dispose,which is an important source of second pollution.Thus,it is urgent to develop such a kind of water treatment agent that are non-toxic > clean and without second pollution.The paper selects starch as a candidate floccutant because it is a degradable, non-toxic, cleanjiatural organic compound.In experiments,the structure of starch is modified in part with physical,chemical and enzyme methods on the basis of keeping up starch's inherent properties.The modified starch has good performance in flocculation besides it has high attraction to environment. Given that the related study is superficial,the paper analyzes the flocculation effect of four classical modified starch.The conclusions are as follows: l)The graft copolymer of starch with acrylamide has good performance hi flocculation. The raw material is corn starch, weight rate of com starch to acrylamide is 2.7:1 and the concentration of initiator is lx10-3mol/L. pH value, reacting temperature have little influence on flocculant of graft copolymer of starch with acrylamide.2) Cationic natural polymer modified starch "CS-8' produced by Mingyang Starch Corporation hi Guangxi province can treat landfill leachate efficiently when hi high concentration. Experimental results indicate obvious flocculate character of CS-8 on kaolin . FNQE is synthesized by putting cationic additives into the parents fraction-starch-acrylamide graft copolymer. The experimental results show that FNQE has ideal turbidity removal efficiency and its performance is superior to that of polyacrylamide. Focusing on municipal wastewater, COD removal ratio is above 70-80% with FNQE. Polymer iron can remove landfill leachate COD 70%-80% with a little additive-Fenton reagent.3)Synthesis of cross-linking starch xanthate is easier than other modified starch.and the cost is less too. When pH is 5 or so ,molecules and ions of xanthate account for 50%respectively .While pH is above 5, the major effect is from ions, or from raolecules-Meanwhile hydroxides' action in the process of precipitate is hidden. Furthmore, the precipitates containing heavy metals can be leached with nitric acid to recover the heavy metals. 4) The process of synthesizing oxidized starch is simple. It almost can't flocculate suspended pollutants.Its lack of adsorbability maybe arises from its small molecules and negative charge, and ferior bridge function.5) Research on action mechanism of modified starch and coordination effect on different components should be strengthened. How to synthesize excellent modified starch so as to suit for water treatment is urgent.Due to wide resources, gradually improving effect and low residual toxicity of starch, evaluation on modified starch in effect and cost must rely on comprehensive environmental and economic profits. Modified starch can be believed to have wide perspective in the field of waste water treatment as flocculent and sorbents of heavy metals.