| There is an amount of sludge produced in the industrial wastewater and domestic sewage treatment. However, the sludge contains large proportion of water, about 95%～97%,which enlarges the volume of the sewage and brings too much trouble in the process of treating the sludge. For the sludge particles are tiny, distributed unevenly, negative electric charged, exclusive from each other, steady, strong combination ability with water, so the specific resistance is large and the performance of dewatering is a little weak, which brings great trouble in processing and treatment of the sludge consequently. Employing the organic macromolecule flocculants to pretreat the sludge,which is a simple but effective method applied widely, can greatly increase the sludge dewatering ability and then make the sludge lose a great deal of liquid in the subsequent mechanical dewatering process.The main results of this thesis were as follows:(1) In the thesis, after reading many books and doing several initial experiments, a cationic sludge dewatering flocculant was synthesized by means of free radical copolymerization of acrylamide and cationic monomer named DAC in aqueous solution by using complex initiator.The influence of experimental conditions on the free radical copolymerization in aqueous solution, including pH value, the concentration of monomers, the mol distribution ratio of monomers,the concentration of initiators,the distribution of initiators, initiating temperature, reaction time, were studied. The optimum conditions of copolymerization were obtained as follows: pH value is 7 (controlled by buffer solution), the concentration of monomers is 20%, the mol distribution ratio to AM and DAC is 6:1, the concentration of initiators is 0.125%,the mass ratio to complex initiator I1 and I2 is 3:1, initiating temperature is 35°C and reaction time is 5 hours. The cationic polyacrylamide was obtained by using this process, with molecular weight 3 million and cationic degree being adjusted from 20% to 30%.The analysis of production cost reveals that the cost of home-made product is 17820 Yuan per ton and 14180 Yuan per ton is saved compared with similar products available in the market.(2) The flocculation performance of home-made CPAM was studied for sludge in condense pool of a sewage plant in the city of ChongQing, China. When the quality concentration of CPAM is 0.325%～0.48%, the adding quality is 0.01%～0.02%, pH value of sludge is 4.5～8.0, CPAM has the ideal treatment effects. Under the optimum conditions, the turbidity removal for upper clean liquid is more than 96%, the colourity removal for upper clean liquid is over 93% and the water content for press cake is decreasing to 68%. In addition, the effects of cationic degree, molecular weight and environmental temperature on sludge dewatering were also researched. The results revealed that the separation effect of sludge particle and water is not better even with excessive cationic degree and molecular weight. The treatment effect is worse when the environmental temperature is lowered to certain degree. Therefore, heat preservation of transfer system for sludge should be paid more attention in winter.The results of the experiment indicated that the dewatering ability of home-made CPAM is inferior to the imported similar products. But it is still economical considering the treatment cost. The analysis of production cost revealed that the cost of home-made product is 106.4 Yuan per ton, thus 53.6 Yuan per ton is saved compared with treatment cost of sewage plant at present.(3) The mechanism of dewatering and flocculant of CPAM for sludge were also studied in this thesis. The results of the experiment revealed that the interaction between flocculant and sludge particle is not only compressing double electroform and charge neutralization effect, but also the adsorption bridge effect.The experiment of absorptive capacity indicated that adsorption isotherm curve of CPAM is S shape. |
