An Investigation On The Composition Of The Solid Residues In Municipal Solid Waste Incineration

With the acceleration of urbanization and the improvement of people’s living standards, the emissions of municipal solid wastes (MSWs) increase annually, and how to effectively treat them has become a global environmental issue. Nowadays, they are commonly treated by landfilling, composting and incineration, of which incineration has been widely employed due to the advantages of volume reduction, quantity reduction and resource recycling. However, highly toxic organic pollutants such as dioxins still cannot be effectively removed hitherto in practice, and the acid gases and solid residues produced from incineration are harmful to the environment. Therefore, preventing secondary pollution by eliminating highly toxic dioxins and by reprocessing flue gas and solid residue predominantly controls the large-scale application of incineration-pyrolysis method.Inorganic substances in the solid residues produced in waste incineration were determined by atomic fluorescence spectroscopy, with the contents converted into equivalent basicities. Then alkali resources were extracted with water as well as dilute and strong acids at high temperature to neutralize acid gases. Water or dilute acids managed to extract 0.78% of the alkali resources, while 2.46% of the alkali resources were extracted with a strong acid. Provided that one ton of solid wastes can generate 150 kg solid residues,0.78% of the alkali resources can neutralize 32.6% of strongly acidic gases based on the flue gas data measured on-site simultaneously. Hence, extracting 2.46% of the alkali resources from solid residues is capable of neutralizing all the strongly acidic gases.In this dissertation, the mechanisms for production of dioxins during the incineration of MSW and their removal were discussed, and then some industrial installations of incineration-pyrolysis worldwide were reviewed. Of the 210 kinds of dioxin congeners produced in waste incineration,2,3,7,8-TeCDD is most toxic. They greatly endanger humans by causing abnormalities, endocrine disorders and chromosome damage. However, dioxins have not been successfully synthesized and no commercial samples are available now owing to high toxicity and unclear formation mechanism. By using the quantum mechanics calculation Gaussian03 program and ab initio methods, the B3LYP/6-311+G(d,p) level was selected to calculate the degradation of 2,3,7,8-TeCDD and to compare the energies required to break the bonds between C-H, C-Cl, C-O and C-C, aiming to reasonably predict and to interpret the degradation steps on the molecular level. Comprehensive analysis of the results suggested that Cl attack was the optimum reaction channel for the degradation of 2,3,7,8-TeCDD.