Urban Sludge Compost Maturity,application Effect And Ecological Risk Assessment

Sludge composting for landscaping can effectively avoid the food chain,prevent harmful substances such as heavy metals from causing harm to humans and animals,it is one of the safest and most efficient methods of sludge treatment and disposal.Using sludge,fly ash,sawdust,garden waste as raw materials,realizing urban sludge mixed composting test,one is the mixing of municipal sludge and fly ash,another is the mixing of municipal sludge with garden waste.Comparing the speed and degree of sludge maturity during composting,and the effect of heavy metal passivation,the experiment yielded the most favorable time for composting and the proportion of added additives.Based on this,the compost product of garden waste mixed sludge is used to pot Rosa rugosa.Study on ecological environmental benefit evaluation and ecological risk assessment of sludge land use.Selection of additives for sludge composting process(including the type of additives and the proportion of additives used),and improve the basic data of landscaping utilization and ecological risk assessment of sludge.Main conclusion:(1)Adding fly ash compost,the results of gray clustering evaluation showed that 0%of fly ash was added,and the compost was not decomposed;Adding 5%fly ash to fundamental decomposed;Adding 15%,25%and 35%fly ash to completely maturity.Before composting,Zn mainly concentrated in Fe-Mn oxide fraction;Cu mainly concentrated in organic combined fraction;Cd mainly concentrated in exchangeable;Pb,As,Ni and Cr mainly concentrated in residual fraction;Hg mainly concentrated in residual fraction and organic combined fraction.Adding 25%of fly ash to compost for 25 days has significant effect on passivation of As and Ni;Adding 35%of fly ash compost for 25 days has significant effect on passivation of Cu,Cd,Pb and Cr,composting for 35 days has a significant effect on Hg passivation,and 40 days of composting has a very good passivation effect on Zn.(2)The gray clustering evaluation shows that 0%of the garden waste was added,and the compost was not decomposed;Adding 10%garden waste to fundamental decomposed;Adding 20%garden waste to better decomposed;Adding 30%,40%and 50%garden waste to completely maturity.Adding 20%-40%of garden waste compost for 35 days has a good passivation effect on heavy metals Hg;Adding 40%of garden waste compost for 25 days has a good passivation effect on pb,30 days has a good passivation effect on As and Ni,45 days has a good passivation effect on Zn and Cu,50 days has a good passivation effect on Cd;Adding 40%-50%of garden waste compost for 35 days has a good passivation effect on heavy metals Cr.Comprehensive analysis,adding garden waste composting time is slightly longer,but the passivation of heavy metals is better,saving resources.Therefore,the compost product with 40%garden waste was selected for the rose pot experiment.(3)With the increase of the amount of compost product added,the number of rose flowering,flowering time,plant height and fresh weight increased first,then decreased slightly.Planting Rosa rugosa is beneficial to improve soil electrical conductivity and pH value,the nutrient content and heavy metal content of compost products are reduced.Adding 10%,20%,30%,40%and 50%of garden waste mixed sludge compost products,the soil nutrient comprehensive index increased by 44.63%,89.89%,102.47%,119.21%and 165.14%,and soil nutrient levels increased from very low to low,low,low,medium and medium.The application of compost products promotes the absorption and enrichment of heavy metals in the roots of Ro,sa rugosa,and the roots have strong absorption of heavy metals Zn,Cd,Pb,As and Cr,stems and leaves have strong absorption of heavy metals Cu and Ni.(4)The results of the index of geoaccumulation and the single factor potential ecological risk index indicate that the heavy metals Zn,Cu,Pb,As,Ni and Cr in the soil are non-polluting and low ecological risk levels.The potential ecological risk index of each treatment comprehensive factor is at the low,low,low,medium,middle and middle ecological risk levels.The index of geoaccumulation and the single factor potential ecological risk index of Cd are both high.