Study On The Reusability Of Landscape Greening Of Municipal Sludge Passivated By Modified Environmental Mineral Materials

The treatment rate and capacity of urban sewage in China has been increasing with the continuous progress of urbanization,which has led to a rapid increase in the number of sewage sludge generated.How to deal with the sludge safely and effectively has become an urgent problem to be solved.The reasonable land use of sludge can not only solve the problem of sludge disposal,but also effectively utilize the organic matter,N,P and other nutrients in sludge.In this paper,the passivator of heavy metal in sludge was prepared by modifying illite and montmorillonite.The dewatered sludge from Jinan West District sewage treatment plant was investigated.Firstly,the influence of modified illite and montmorillonite on the four heavy metals of Cu,Pb,Zn and Cr in sludge was studied.The best passivation conditions were determined by orthogonal experiment.The effect of stabilized sludge on ryegrass growth and bioavailability of four heavy metals was studied by passivation was studied by ryegrass planting experiment.The accumulative release characteristics of nutrients and heavy metals were simulated by soil column leaching experiment,and the release process was studied by different kinetic models.TCLP method was used to evaluate the risk of heavy metal migration in the land use of passivated sludge.Finally,the passivation mechanism of modified silicon-containing materials was analyzed.The main experimental conclusions are summarized as follows:1. The surface area of illite and montmorillonite increased by 34. 3%and 36.5%,EC by 18%and 27.3%,CEC by 27.4%and 14.2%,respectively,after being burned at500?and then modified in the 1.0 mol/l Na₂CO₃solution at a ratio of 1:10.2. The dewatered sludge of Jinan West District sewage treatment plant was rich in organic matter,N and P,and its fertilizer efficiency was fully in line with the relevant standards for landscape use.The content of Cu,Zn,Cr and Pb were far higher than those in the background soil,but lower than the standards for landscape use.The dewatered sludge could be used for landscape use in neutral and alkaline soil.3. Illite and montmorillonite showed different passivation effects on four kinds of heavy metals. The single factor experiment results showed that the passivation effect of illite and montmorillonite could be improved by modification treatment.The best passivation effect for heavy metals could be obtained with the 10%?20%illite addition.When adding 10%modified illite,the residue of Zn,Cr,Pb and Cu increased by 9%,5.9%,9%and 5.3%,respectively.Adding 5%?20%montmorillonite could obtain the best passivation effect,and the proportion of residual state of four heavy metals increased.4. Taking illite addition,montmorillonite addition and passivation time as three factors,three factors and three levels of orthogonal test were designed. The results showed that the most important affecting factor on Cu immobilization was the amount of illite powder,the amount of montmorillonite powder on the Cr passivation,and the passivation time on the Zn passivation.According to the experimental results,the optimum passivation conditions were determined as 10%illite powder,5%montmorillonite powder and 15 days passivation time.5. The fertilizer effect of passivated sludge was reduced after treated with modified illite and montmorillonite. However,it still conformed to the relevant standards of sludge treatment for landscape greening in urban sewage treatment plant?GB/T23486-2009?.In the ryegrass planting experiment,the plant height,tiller number,chlorophyll content,leaf dry and wet weight of the passivated treatment were higher than those of the control group.The content of heavy metals in the underground part of ryegrass was higher than that in the aboveground part.6. The results of leaching experiment showed that passivation treatment could significantly reduce the leaching rate of heavy metals in sludge,and the order was:Zn>Cu>CR>Pb.The heavy metals concentration in the leaching solution from passivation treatment,non-passivation treatment and control treatment were all lower than the class IV limits of groundwater quality standard.The first-order kinetic equation,the modified Elovich equation,the double constant rate equation and the parabolic diffusion equation were used to study the cumulative leaching amount of heavy metals and nutrients in the leaching solution.It was found that the heavy metal release under the leaching condition was not a simple single factor control reaction process,but a multi-factor control process.7. According to the results of relevant indicators?pH,EC,BET?in the soil,the passivation of silicon containing mineral materials to heavy metals was mainly due to the adsorption caused by large specific surface area and the formation of hydroxide precipitation due to the increase of pH.