The Investigation Of Dyeing Sludge Conditioning And Deep Dehydration

There are lots of dyeing wastewater produced from the treatment of dyeing wastewater every year in China, a country has prosperity textile industry. The dewatering of dyeing sludge is very difficult because of its complex composition, small particle size and high water content. The sludge dewatering process accounts for a major portion of the cost of the sludge treatment and represents significant technical challenges. So it's very important to find a high efficient dewatering technology for dyeing sludge.To solve the difficulties of dyeing sludge dewatering, we applied pretreatment in sludge conditioning to improve its dewatering properties. Inorganic polymer coagulant, a new type of coagulant, has been applied in wastewater treatment a lot, and has shown superior performance in the decolorization and turbidity removal. But its application in sludge dewatering is still less. In order to improve the dehydration performance of dyeing sludge, this study applied polyaluminium chloride(PAC) and polyferric sulfate iron(PFS), which with relatively low price, in dyeing sludge conditioning.When applying PAC and PFS in dyeing sludge conditioning, it was found that both of them can effectively improve settlement and filtering performance of dyeing sludge, and both of them are major indexes of sludge dewatering performance. And the conditioning effect of PFS was better. By analyzing pH value, zeta potential, particle size, bound water content and the compressibility coefficient, it was found that inorganic polymer coagulants can effectively regulate the pH value of sludge suspension, reduce zeta potential, make the small particles agglomerate into larger flocs. But the flocculation bridging effect is not strong, the main effect was neutralization potential. In addition, inorganic polymer coagulants can also effectively reduce sludge compressibility and the content of bound water. The sludge conditioned with PFS has better performance. The study in former literatures indicated that sludge conditioned with many kinds of coagulants often had better performance than sludge conditioned with one kind of coagulant. PFS was combined with cationic polyacrylamide(CPAM) and lime respectively in this study, and the optimal ratio was obtained by orthogonal experiment. It turned out that when filtering with low pressure(0.1MPa), both complex scheme can effectively improve the filtering performance of dyeing sludge, but when filtered under high pressure(filtration pressure 0.6MPa, expression pressure 2.0MPa), although the combination of PFS and CPAM can effectively reduce the specific resistance of cake, but the water content of filter cake was even higher than sludge conditioned with PFS alone. The combination of PFS and lime not only can further reduce the cake resistance, but also can further reduce the moisture content of filter cake. In the last, applying the optimal scheme(10%PFS+10%lime) in dyeing sludge conditioning, and studying the effect of different operation conditions on dyeing sludge dewatered by continuous pressed filtration. It was found that with the increase of filtering pressure, the filtration efficiency gradually increased, but the moisture content of filter cake has no significant change. When starting expression before the filtering into the compaction period, the processing capacity can be effectively improved. An appropriate improvement of expression press can effectively improve the expression efficiency, but when the expression was too high, not only the filtering efficiency won't be improved, but also the cake moisture content will increased.