Transfer And Transformation Of Heavy Metal,carbon,nitrogen And Phosphorus In Sludge During Thermal Conditioning

With the increase of sewage treatment volume in China,sludge production is also increasing.The problem of how to properly dispose of sludge needs to be solved.From a long-term perspective,the land use of sludge can not only completely dispose of sludge,but also achieve the recycling of sludge.However,before the sludge land is used,it is necessary to stabilize or remove heavy metals in the sludge and reduce the ecological risk of heavy metals in the sludge.Sludge thermal conditioning technology can realize the stabilization of heavy metal form,reduce the moisture content of sludge,reduce the transportation cost of sludge,and thermal conditioning technology can decompose the organic matter in the sludge and provide rich inorganic carbon and nitrogen for the plant.Phosphorus nutrition,these are conducive to the realization of the land use of sludge.In this study,the effect of thermal conditioning on the physicochemical properties of sludge was investigated from the aspects of thermal conditioning,sludge reduction,migration and transformation of heavy metals,and transport and transformation of carbon,nitrogen,and phosphorus.At the same time,the factors that caused these effects,thermal conditioning temperature and thermal conditioning time were studied.The results show:(1)Thermal conditioning can greatly reduce the sludge,and improve the dewatering performance of the sludge.Under the conditions of 240? and 60 min,the sludge centrifugal reduction rate reaches 71.34%,the centrifuged water content is61.04%,and the temperature is higher.The longer the time,the greater the reduction rate of sludge and the lower the moisture content.However,from the perspective ofenergy conservation and treatment effect,the temperature is set to 180? and the time is 60 minutes,which is appropriate.Centrifugation under the same thermal conditioning conditions is more effective than suction filtration on sludge reduction.(2)Thermal conditioning has an impact on the content and form of heavy metals in the sludge.The proportion of heavy metals entering the liquid phase is always below 1.4%.The heavy metals in the solid phase are enriched and enriched at 240?for 60 minutes.The rate reached 146%,which is detrimental to the stabilization of sludge.The form of heavy metals in the solid phase also changed,especially at 240?and 60 min,the proportions of residuals(F5)of Cu,Pb,and Cr increased by 10.9%,7.05%,and 2.97%,respectively.The proportion of Ni in the F5 state has declined,mainly due to the transition from the direct risk state(F1+F2)and the steady state(F5)to the potential risk state(F3+F4).Thermal conditioning reduced the RI of heavy metals in sludge,but the risk level did not change.(3)Thermal conditioning has a certain effect on the migration and transformation of carbon,nitrogen and phosphorus in sludge,but the degree of transfer is different.Under the conditions of 240? and 60 min,38.51% of carbon enters the liquid phase,and 58.19% of nitrogen enters the liquid phase.Only 17.5%of the phosphorus enters the liquid phase.