| Flocculation is the most commonly used method of water treatment. The development of new type of flocculants with excellent performance, safety and environmental protection is a heated issue. This topic is made from natural polymer corn starch as the main raw material, by modification of grafting and crosslinking to prepare a new type of flocculant. Single factor and orthogonal optimization experiments were to explore the flocculant conditions. The structure and properties of flocculant were characterized by means of infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis and X-ray diffraction. Flocculation experiments in kaolin suspension, Cr(VI) aqueous solution together with dewatering of activated sludge were carried out.The main findings are as follows:(1) Preparation of corn starch-graft-polyacrylamide:Took5g of corn starch dissolved in a certain amount of water, gelatinization at90℃for30min, and then adjusted the water bath to the reaction temperature. The system was under nitrogen protection for30min and then added initiator (NH4)2S2O8. After5minute slowly added2mol/L acrylamide aqueous solutions to the system, and the reaction time was5h. Three different proportion of grafted starch were synthesized, the mass ratio of Starch and acrylamide was respectively5:2,1:1,1:3.(2) Flocculants Preparation:Using starch-graft-polyacrylamide (Mass ratio of starch and acrylamide was1:1) crosslinked with cationic starch, to explore the best preparation conditions. Optimum conditions:the mass ratio of cationic starch and starch-graft-polyacrylamide was3:1, the amount of crosslinking agent was0.35mL/g, reaction temperature was60℃, and reaction time was2.5h. The surface of synthetic flocculant was rough and even had wrinkles. The flocculant had a lower and wide range of pyrolysis temperature, showed that thermal stability was became deteriorated.(3) The best dosage of flocculant for kaolin suspension flocculation was32mg/L, and then transmission rate of upper supernatant was89.0%. Upper Supernatant transmittance was increasing with the increase of the deposition time, and almost reached equilibrium after5min. When the system pH at2had the best flocculation effect for the kaolin suspension, and then the zeta potential of kaolin particles were at the minimum absolute value. The higher the temperature the performance of flocculate was better. And while the temperature increased the growth rate decreased. Synthetic flocculant had better flocculation performance than PAM. Removal rate of Cr (VI) reached the highest46.4%when Flocculant dosage was9.3g/L. The initial concentration of Cr (VI) and pH of the system were very important impacts for Cr (VI) removal, and when the pH of the system was4.00had the highest removal rate50.4%.(4) Flocculant can improve the performance of sludge dewatering. The flocculant dosage was a very important impact on activated sludge dewatering performance. When the dosage of flocculant was2g/L the settling characteristics of the activated sludge was best. The modified starch flocculant had an approximate dewatering compared with polyacrylamide. |
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