| In this paper, the effects of alkali concentration, material ratio, pH value and reaction temperature on the process of the preparation of chitosan were researched, in this process, shrimp shell was chosen as the research object. The effects of hydrogen peroxide concentration on the molecular weight were also studied when it was used to degrade the chitosan. In addition, the relations between CS molecular weight, the deacelation degree, dosing quantity, pH value, hydraulic conditions and organic matter, turbidity, COD, removal of residual aluminum were also researched in the enhanced coagulation process. With the high speed development of industrial, the amount and the type of organic pollutants in most of the rivers and lakes in China continues to increase. These trace organic matters in the water could not be removed fully with the traditional flocculant and it could also lead to the remainder of metal aluminum, which is harmful to the health of human body. Due to the characteristics of natural non-toxic, CS has become a hot research topic in wastewater treatment. Its excellent flocculation performance was used in this research, through compound with inorganic flocculant, its application in water treatment was investigated.The chitin was prepared with the shrimp shell in Qianjiang as the material, and then the calcium and protein were removed with3.75%hydrochloric acid and4.5%sodium hydroxide respectively. The reaction conditions to make the high deacelation degree of CS were as follows:the mass fraction of the sodium hydroxide solution is48%, the alkali ratio is1:9, reaction temperature is90℃, and reaction time is2.5h. The result show that the deacetylation degree of CS can reach more than85.3%, the CS molecular weight is6.23×105. The CS samples were characterized through the infrared spectrum analysis and X-ray diffraction analysis and the degradation mechanism were also analyzed.The adsorption capacity of the CS to organic matter in water is investigated, the result show that the COD removal rate was the highest when the deacelation degree of CS was78～85%, the molecular weight was5.83×104, the pH value was6.0～6.5, according to the principle of inorganic, organic, inorganic and organic composite, flocculation experiment was perform to simulate the surface water with the PAC, CF-PAC, CS and PAC/CS, CF-PAC/CS. The results show the simulated water could r -each better effects when it was treated with the primary flocculant CF-PAC (20ppm) and coagulant aid CS (0.10ppm),in the condition of quickly stirring intensity300r/min (60s) and slowly stirring intensity60r/min (10min), the turbidity was below0.4NTU, the content of aluminum ion was only0.041mg/L, the content of PAC was76.02%lower than traditional,70.07%lower than PAC/PAM, the cost to treat one ton was slightly lower than traditional flocculant PAC.The flocculation mechanism of composite flocculant was briefly analyzed. The CF-PAC component in composite flocculant hydrolyzed firstly and then polymerized in water, in this process, iron ion hydrolyzed rapidly first, then the aluminum ion hydrolysis, due to negatively charged colloid particles in water, the polynuclear hydroxy which was formed with iron ion and aluminium ion after hydrolysis is electropositive, which could absorb the colloidal particles in water quickly. There are large numbers of hydroxyl and amino with electropositivity on the molecular chain of CS after hydrolysis,thus enhance the electric neutralization in the flocculation process largely, at the same time, the long molecular chains in CS can be quickly connected adjacent particles to form a mesh structure, CF-PAC and the synergy of CS with electric neutralization, bridge and net-catch combined together to short the flocculating settling time and improve the flocculation efficiency. |
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