| With the increasing contradiction between industrial production and environmental pollution, environmental governance, along with energy saving and emission reduction has attracted much attention. A lot of sludge is produced in the process of treating sewage and waste water.The moisture content of this sludge is up to 95%, which not only causes the sludge to occupy a large space, but also brings inconvenience to the subsequent treatment,and also pollute the environment. Therefore, it is a current research hotspot to improve the dewatering performance and reduce the volume of sludge.At present, the flocculant of the sewage plant for sludge treatment is mostly synthetic flocculant, such as polyacrylamide(PAM) and poly aluminium chloride(PAC), which they or the generated monomer after degradation is toxic and not easy to degrade, has brought great harm to the living environment and human health. Moreover, some countries have forbidden the use of PAM in the water treatment, so it is significant to develop and study the sludge dewatering flocculant without PAM. In this paper, the green high efficient sludge dewatering flocculants were synthesized by using cationic monomer to modify the natural polymers CMC and Chitosan, and the application of these flocculants in sludge dewatering were rarely reported.Firstly, cellulose is the most abundant natural polymer in nature. Sodium carboxymethyl cellouse is widely used derivatives of cellulose, which takes negative charge after the ionization in water. The sludge particles also have negative charge, so it is more prefer to the charge neutralization of the flocculant with positive charge. Herein, the amphoteric polymeric flocculant(CMC-g-PDMC) was synthesized by sodium carboxymethyl cellulose modified by the quaternary ammonium salt with positive charge(DMC) and aqueous solution polymerization method using potassium persulfate as a free radical initiator. The effects of initiator dosage, reaction time, reaction temperature, monomer mass ratio on the grafting ratio and grafting efficiency of the synthesized polymer were investigated by orthogonalexperiments. The optimal reaction condition was confirmed.Secondly, chitosan is the only nature polymer with positive charge in nature, and has been widely used in sewage and sludge treatment. But its application in sludge dewatering has been limited because of its poor solubility and low positive charge density. In this paper,the flocculation effect was improved by grafting copolymerization of chitosan and cationic agent(dimethyl diallyl ammonium chloride). The cationic chitosan flocculant(chitosan-g-PDMDAAC) was synthesized by aqueous solution polymerization with ceric sulphate as an initiator. The effects of initiator dosage, reaction time, reaction temperature,monomer mass ratio on the polymerization effect were investigated by orthogonal experiments. The optimum polymerization condition was determined.Lastly, flocculation capacity of the two kinds of flocculants to municipal sludge treatment was evaluated by filter cake moisture content, specific resistance in filtration,sludge index and transmittance of filtrate. The effects of the dosage of flocculant, grafting rate, cationic degree, p H value, temperature on the sludge dewatering performance were investigated in the sludge treatment by comparing with the common flocculants CPAM,PAM and PAC. The results showed that the flocculation capacity of the cationic chitosan flocculant was better than the other flocculants. The water content of sludge was decreased from more than 95% to the moisture content of the filter cake about 68%.In conclusion, two kinds of modified natural polymer flocculants were synthesized, and were confirmed with good flocculation performance in the actual sludge dewatering, and which broadened the application of natural polymer. So this research has practical value. |
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