Experimental Study On Treatment Of Residual Sludge By Constructed Wetland

The excess sludge,as a by-product of the municipal wastewater treatment plant,contains not only the harmful substances such as heavy metals and bacteria,but also other nutrients required for plants including large amounts of organic substances,nitrogen,phosphorus and potassium.With the acceleration of urbanization process,the growth rate of sludge volume is more and more fast.And the excess sludge would pollute the environment and cause the resources wasting without any treatment.Even the simple treatment would cause serious secondary pollution and bring new difficulties to the comprehensive environmental management.Hence,how to deal with the excess sludge containing sludge reduction,harmlessness,stabilization and final resource utilization,attracts more and more attention.Constructed wetland is a kind of natural treatment technology which has a better purification and stabilization effect on excess sludge.Stable sludge is suitable for land use and is more economical and environmentally friendly than traditional methods such as landfill and incineration.Based on the analysis of the characteristics of the excess sludge in the urban sewage treatment plant,three units of vertical flow constructed wetlands were designed,namely,I unit was reed,progressively-graded,?unit was unit reed,anti-graded,?unit was canna,anti-graded.The effects of graded and plant species on the leachate purification and the stabilization on the accumulated sludge were investigated.The differences of heavy metals enrichment by the wetland plants were also studied.The results showed that the treatment effect of leachate through artificial wetland system is obvious,and the effect on the organic matter of leachate of ? unit is better than other two units.The order of denitrification is from ? to,II,I unit.The types of wetland plants have an effect on the treatment of excess sludge.The results showed that the removal rate of organic matter,TN and TP of was higher than that of ? unit.The water content of sludge was positively correlated with organic matter and sludge TN.Reed had better effect on the mineralization and stabilization of accumulated sludge.Reed and Canna can absorb and enrich heavy metals and the roots absorbed the most than stem and leaves.The absorption of Zn of root is higher than other four elements.The absorption of heavy metals was different in different plants,and Cr and Cu were significantly different,Sig.<0.05,and Pb and Zn was extremely significant difference,Sig.<0.01.It was found that the thickness of accumulated sludge is linear with running time.The content of EPS in the system was low,and preliminary estimated the system was not to be clogged.The results show that the vertical flow constructed wetland system has a more obvious dewatering effect on the excess sludge,and can effectively promote the sludge stabilization.The research of this study has a good reference and guidance significance for the further utilization of excess sludge.