Study On Dewatering Flocculants Of Chitosan Grafted Acrylamide And Chitosan-acylamide Complex

A great deal of sludge produced during waste water covered with sediment of living and industrial waste water which composed of a lot of pathogen, heavy metal, organic contamination and other pollutants leading to the second pollution. If sludge are treated inappropriately, deleterious will move and empoison the soil and river though infiltration and flow along the earth's surface, which has potential harm to the environment and people's health. One of the traits of sludge is high water content, often from 95% to 99%. It makes sludge bulky and runny, hard to sequent dispose. In order to benefit the following landfill, incineration agriculture and transport, the first step of dealing with sludge is dewatering. But, the sludge particle covered with negative charge which exclusive from each other forming a steady system, thus water absorbed tightly by the particle through physical or chemical action is hard to separate only by mechanical power.Chemical conditioning-adding flocculant changing the physical and chemical characters of sludge separating water and solid is adopted widely in home and oversea. The general sludge dewatering agent is polyacrylamide. It is an artificial agent and the degraded matter and monomer of it are harm to people. While, nature matter chitosan owning the advantages of biocompatibility, easy biodegradable and being abundant in nature becomes available green flocculant. But, the molecular chain is not long enough, the molecular weight is not heavy and it can't dissolve in water. Two ways have been tried to amend, modify chitosan by chemistry reaction and complex with other flocculant reaching the aim of reduce the dosage and improve the results.A grafting reaction conducted with chitosan and acrylamide initiated by ceric ammonium nitrate(CAN) to prolong the molecular chain and introduce the active group which can enhance the flocculating ability. This reaction was affected by the solid content, the ratio of reactor, the concentration of initiator, temperature and some other factors. Regard the percentage of adding on as an index, intersection experiments show when all the reagents contents are 11%, put nitrogen 20 min, reaction time is 3.5 h, m (CTS): m (AM) =1:8, the concentration of initiator is 0.06% and the temperature is 45℃, the reaction have the best value of 396.4%.Intuitionistic analysis show the most important factor affecting the reaction is the ratio of reactor, then the concentration of initiator, the last is temperature. Infrared spectrum and sanning electron microscope (SEM) indicated that a new matter of CTS-g-AM had been produced. And this new matter had more efficiency on turbidity removing with the removing rate of 94.9%, the same index of chitosan is just 74%.No one grafted chitosan had been produced as a commodity yet, in order to apply this nature flocculant, the cationic polyacrylamide(CPAM) was used together with it, that is complex flocculant. polyferric sulfate(PFS) was also used with polyacrylamide to compare with the former. The ratio and dewatering effect of these two complex flocculants had been studied. The results show PFS-CPAM with the dosage of 40 mg/L PFS and 200 mg/L CPAM had the best quality of filtrate with removing rates of corlority, turbidity and COD reached 79.8%, 90.5% and 77.9%.Although CTS-CPAM had less improvement on filtrate quality, it had the best performance on dewatering amount in every independent experimnet with the dosage of 20 mg/L chitosan and 200 mg/L CPAM and the best dewatering rate is 61 ml/100 ml sludge. Whether dewatering amount,filtrate quality or filtration ability indicated two kinds of complex flocculants had better performance than single flocculant. This is the result of complex flocculant exerting the advantages of two kind flocculant and having some interaction.Modified chitosan and chitosan complex flocculant had better flocculate ability than chitosan itself and had an exploitable prospect. This should attribute to the special configuration of chitosan. The active amido and hydroxide on the chain side and other advanced structure. According to the trend of dewatering effect changed with adding dosage of chitosan, some mechanism had been presumed, that was chitosan with moderate molecular weight had both function of counteracting charge and building bridge.