Effects Of Municipal Sludge Application After Leaching On Growth Of Chinese Cabbage And Soil Quality

With the increase of sewage treatment capacity in China,a large amount of municipal sludge needs to be disposed every year.The common disposal methods include stacking,landfill and incineration.It is the best dispose way to use sludge for agriculture from the perspective of sustainable development.This paper takes dewatered sludge of Beijiao and Yangjiapu sewage treatment plant in Taiyuan as the research object,optimized mixed chelators（MC₄）was adopted to elute two kinds of sludge.The sludge before and after elution was added to the farmland soil with different mass ratio（0.3%,1%,3%）,and greenhouse cultivation experiments and pot experiments were carried out.The effects of mass ratio on Chinese cabbage growth,soil heavy metals content and physicochemical properties were investigated.The main research results are as follows:（1）The removal efficiency of heavy metals from the sludge of Beijiao and Yangjiapu plants by using mixed chelators was better than that of single leachate,and the removal efficiency of MC₄（GLDA:CA=1:5）was the best.The removal efficiency of Cd,Cu,Zn,Mn and Cr in Yangjiapu sludge were 1.25%,11.05%,97.71%,95.40%and 27.90%,respectively,when the concentration of MC₄ was0.2 mol·L^-1 under the optimal molar ratio,vibration time and p H value.The removal ratios of Cd,Cu,Zn,Mn and Cr in the Beijiao sludge were 14.09%,71.01%,46.03%,76.70%and 29.35%,respectively.The MC₄ with high concentration was selected for removal of heavy metals from municipal sludge due to its high efficiency and environment friendly.（2）The aboveground biomass of Chinese cabbage was significantly increased at the addition of municipal sludge.The heavy metals content of Chinese cabbage decreased effectively by adding leaching sludge.The Cu and Mn contents of Chinese cabbage in the underground part had little change among different treatments.Zn content of the underground part in the first season was much higher than that in the second season,whereas Cr content of the underground part in the first season was much lower than that in the second season.Except Ni,the contents of other metals in the aboveground part of Chinese cabbage in the second season were higher than those in the first season.（3）The direct agricultural use of sludge has obvious influence on the heavy metals content in soil.In this study,five index metal elements of Cu,Zn,Cr,Ni and Mn in soils treating with different sludge were determined.It was proved that the contents of Cu,Zn,Cr and Ni were all lower than the risk screening value of soil pollution risk control standard for agricultural land（GB 15618-2018）,which provided a theoretical basis for the agricultural use of sludge.（4）The effect of municipal sludge on soil nutrient content was obvious.Except for cation exchange capacity（CEC）,the physicochemical properties of soil such as organic matter,alkali-hydrolyzable nitrogen,total phosphorus and available phosphorus increased significantly with increasing sludge mass ratio.The supplement effect of soil nitrogen was very obvious.According to the soil nutrient classification standard,the overall fertilizer of the soil was significantly improved.It can be seen that municipal sludge has a good supplemental effect on soil fertility.