The Migration And Transformation Behavior Of Pb During Co-disposal Of Municipal Solid Waste Incineration Fly Ash And Sewage Sludge

The world today is facing two major problems of energy resource shortage and environmental problems.In December 2020,the Central Economic Work Conference put forward the goal of"China aims to reach the peak of CO₂emissions before 2030,and strive to achieve carbon neutrality before 2060".Coping with climate change and low-carbon transformation and development have become major strategies of China.China is actively,orderly and effectively carrying out research and engineering practice around the goal of"carbon peak"and"carbon neutralization".Municipal solid waste incineration fly ash and sewage sludge because it contains a variety of pollutants（including heavy metals,highly toxic dioxins,etc.）,how to scientific disposal has become a worldwide problem.Therefore,the search for harmless,reduction,stabilization,resource disposal has become an increasingly concerned problem.In recent years,the rapidly developing technology of industrial kiln collaborative disposal of solid waste has become an important product under the current circular economy development mode.Ready-made industrial kilns in various industries can reduce the construction and operation costs of solid waste disposal,and replace some of the fossil fuels or production raw materials required for industrial production.It also improves industrial economic benefits while realizing the recycling of solid waste and reduces carbon emissions on the basis of energy saving and consumption reduction.In this paper,aiming at the demand for"reduction,resource utilization,and harmless treatment",guided by low operating costs and high promotion value.Taking advantage of the resource utilization of municipal solid waste incineration fly ash,the technical idea of using sewage sludge as low-quality fuel and co-disposing in cement kiln was proposed.Although this technology is beneficial to reduce the volume of waste and effectively decompose dioxins and fix heavy metals.The high content of chlorine,sulfur and heavy metals in municipal solid waste incineration fly ash and sewage sludge will lead to high-temperature plugging,crust and corrosion of cement kilns,reduce the quality of cement products and seriously limit the development of this technology.Based on this,it is necessary to explore the migration and transformation rules of heavy metals in the co-disposal process under different experimental conditions（mixing ratio,combustion temperature）and the ecological risk of bottom ash to the environment.In order to provide a theoretical basis for the practical project of co-disposal municipal solid waste incineration fly ash and sewage sludge in cement kiln.In this paper,municipal solid waste incineration fly ash and sewage sludge are selected as typical municipal solid wastes,and a co-disposal experimental system is established,which is mainly divided into three parts:gas distribution system,tube furnace incineration system and flue gas absorption system of heavy metals.The tube furnace was used to simulate the high temperature conditions of a cement kiln for co-disposal experiments.By changing the temperature and the mixing ratio,the impact on the migration and transformation of Pb was investigated.The combustion temperature was set at 1000°C,1100℃,1200℃,the mixing ratio（municipal solid waste incineration fly ash:sewage sludge）was set to 10:0,8:2,6:4,4:6,2:8,0:10.Explore the distribution characteristics of Pb under different experimental conditions in the process,as well as the occurrence forms and ecological risks of Pb in bottom ash.The results show that under the experimental conditions,the total concentration of Pb in the residue after co-disposal is significantly lower than that in the raw material.With the increase of temperature,the concentration of Pb in the bottom ash decreases,and the concentration of Pb in municipal solid waste incineration fly ash is on the contrary.The change of Pb concentration in flue gas is not obvious.The concentration of Pb in the bottom during co-disposal is mostly lower than that of municipal solid waste incineration fly ash and sewage sludge disposal alone,and the concentration of Pb in the bottom ash decreased with the increase of the sewage sludge mixing ratio.Pb in materials and bottom ash mainly exists as non-toxic residual components.With the increase of temperature and mixing ratio,the conversion of Pb from unstable state to stable state,indicating that controlling experimental conditions（temperature and mixing ratio）is an effective way to fix heavy metals.In addition,four different environmental risk assessment methods were used to evaluate the results,and it found that the amount of pollution of the bottom ash after disposal is lower than that of the materials,and the ecological risk of co-disposal is lower than that of separate disposal.It can be seen that the co-disposal of municipal solid waste incineration fly ash and sewage sludge can help to improve the solidification rate of heavy metals.By controlling the mixing ratio and temperature,it is beneficial to solidify heavy metals and reduce the harm of bottom ash to the environment.The research results of this paper can further understand the migration and transformation characteristics of heavy metals in the co-disposal process of municipal solid waste incineration fly ash and sewage sludge,help to better formulate policies related to co-disposal and guide downstream control Pb emission technology,and promote the development of municipal solid waste incineration fly ash and sewage sludge harmless treatment and resource disposal in a green,low-carbon and sustainable direction,in order to provide theoretical basis and process reference for the engineering practice of cement kiln co-disposal of municipal solid waste incineration fly ash and sewage sludge.So that cement kiln co-disposal of solid waste technology has been widely promoted and applied in China.