| Municipal sludge treatment and disposal technology in the current years meet the bottlenecks because of the improvement of people's environmental quality requirements.Meanwhile,"sludge disaster" have become urgent problems that need to be cracked.However,the original flocculation performance of polyacrylamide(PAM),widely used in sewage and sludge treatment,is difficult to meet the requirements of new technical indicators for some limitations.Its slow degradation and products make a severe environmental accumulation risk.Consequently,it has theoretical and practical significance to systematicly study the flocculation mechanism of PAM on sludge,modification method for improving PAM flocculation performance,and the reduction of environmental and toxicological characteristics for the effective treatment and disposal of municipal sludge to improve the PAM flocculation performance and environmental friendliness.Therefore,the following work was conducted in this paper.To begin with,the effects of different properties of PAM on sludge conditioning were systematicly studied,and the action mechanism of ionic degree and molecular weight of cation polyacrylamide(CPAM)to the sludge particles was analyzed.The results demonstrated that the molecular weight of CPAM and its ionic degree played different roles,not independent but coupling relationship,in sludge flocculation and dewatering.Thereinto,ionic degree of CPAM,determining the ability of providing cationic electrolytes,played an important role in the destabilization and cohesion of negative charged sludge colloid,and also played a key role in sludge conditioning.In addition,the method of modifing PAM with calcium/magnesium ion was studied and the flocculation performance of the modified product(calcium/magnesium ion-PAM)was designed and optimized.The calcium/magnesium ion-PAM polymeric modification mechanism was explored through molecular structure characterization;conditioning effect of calcium/magnesium ion-PAM on sludge was analyzed on the basis of the specific resistance of sludge,Zeta potential,capillary suction time(CST),the supernatant turbidity and filtrate viscosity test;the mechanism of calcium/magnesium ion-PAM to sludge flocculation was analyzed by using molecular structure characteristics.The results indicated that the molecular structure of calcium/magnesium ion-PAM was formed through cross-linking between the carboxyl group on the PAM chain with the multinucleated hydroxyl bridge ions of calcium and magnesium hydrated ions;provide more effective positive charges from multicore hydroxyl bridge ions in the core were electrically neutralized with the negatively charged colloid particles.The full hydrolysis of polynuclear olation complex ion made PAM polymer molecular chain crosslinked completely opened,this subsequently made bridging and net sweeping role fully exerted,so the routine use of flocculation performance was significantly better than that of CPAM;In this research,three kinds of calcium/magnesium ion-PAM was prepared,which molecular weights were 5.10×106 Da,6.62×106 Da and 6.26×106 Da respectively;Their effluent turbidity removal rate was more than 99%,and the reducing rate of specific resistance of sludge was more than 97%.Finally,series of variation laws were investigated including the natural degradation of calcium/magnesium ions-PAM and CPAM in soil,its toxicological properties on plants,animal,and its influence difference on the seed germination,growth of plant and survival,growth and reproduction of earthworm.Then,the influence mechanism of the molecular structure of PAM on its degradation was also discussed.The results showed that calcium/magnesium ions would promote the degradation of PAM;the degradation rate of calcium/magnesium ion-PAM was 30?50%faster than that of other CPAM with shorter environmental survival time,and low risk of environmental and biological effects of long-term cumulative.Therefore,the calcium/magnesium ion-PAM was more environments friendly. |
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