Effect Of Municipal Sludge Biochar Amendment On The Behavior Of Polycyclic Aromatic Hydrocarbons And Greenhouse Gas Emission During Rice Planting Period

The disposal situation of sludge is becoming a serious problem as the production of municipal sludge increase year by year.Municipal sludge biochar?MSB?preparation and usage as soil fertilizer is a kind of sludge treatment and disposal method,which is good for the harmless,stable and resourceful of sludge.Polycyclic aromatic hydrocarbons?PAHs?,contented in MSB,have the potential of being released into ecological system with the agricultural use of MSB.Meanwhile,its environmental behaviors,which do harm to ecological system and human's health,will be affected by MSB duing to the adsorption ability of MSB.However,to our best knowledge,there is little study concerning about the content of PAHs in the MSB??15PAHs?,PAHs content in its leachate,and PAHs environmental behaviors after agricultural use.Therefore,the following works were conducted in this study.Firstly,the optimal pyrolysis conditions of MSB for agricultural use were determined by analyzing its physical and chemical properties and leaching toxicity.It was found that the better MSB with low volatile,environmental risk and high ash and fix carbon was obtained at 650 ? for 2 h.In addition,the potted plant experiment was conducted by adding paddy soil with various MSB content.The result showed that MSB would change soil particle structure and inhibit the microbial metabolic activity,especially for those organisms which used WSOC as the sole carbon source,promoting the growth of rice and the reproduction of PAHs degradation bacteria;MSB changed the distribution of PAHs in soil,increased soil?16PAHs.When the MSB applied ratio ws?10%,the toxic equivalent concentration of PAHs increased significantly,and the soil health risk increased.Finally,greenhouse gas emissions from potted rice were measured.Its results indicated that the emission of CO₂ decreased first and then increased with the increase of the MSB applied ratio while the emission reduction effect of CH₄ and N₂O increased gradually.MSB has significant effect on greenhouse gas emission reduction when the ratio is<10%.From the view point of agricultural suitability,the optimum application ratio of MSB is 5%.