Municipal Solid Waste Incineration Bottom Ash: Experimental Study And Thermodynamic Analysis

Incineration is an effective method of treating MSW. However, it is not the last stage of MSW disposal. With the growth of incineration of MSW, the disposal of the increasing amount of bottom ash is becoming a new environmental issue. A societal goal towards bottom ash management is focusing on converting the ash into useful products without any negative impact on environment and human health.The thesis is aiming at investigating the characteristics of MSWI bottom ash as well as its potentials of reutilization. Two kinds of the sampling strategies were carried out to collect different bottom ash streams, including field sampling in Tianjin and Amsterdam incineration plants and experimental sampling by combustion of the synthetic mixtures of basic and specific wastes in a laboratory set-up simulating the process in a stoker furnace. The ash samples were respectively analyzed in terms of their characterization through physical separation technologies, chemical analyses, toxicity leaching tests, and thermodynamics calculations. The influences of the specific wastes on chemical properties of MSWI bottom ash were analyzed, such as small WEEE, shredder fluff, sewage sludge, and plastics packaging wastes.Meanwhile, resource potentials of reutilizing MSWI bottom ash and the related management policies were investigated.The results obtained indicated that bottom ash could be a well-graded granular with a continuous grain size distribution and low proportions of non-plastic fractions. 75μm-28mm size fraction accounted for 90%-95% of the bottom ash weight, and smaller than 75μm size fraction was about 5%. Tianjin bottom ash was basically suitable to be reused as road base aggregates with the exception of the undesirable compatibility and high organic content in the fine fraction. Compared to Tianjin bottom ash, Amsterdam ash contained more glass, synthetic ceramics, and more metals (9%-13% of ferrous metal and 2.1% of nonferrous metals), and showed strong leachabilities of Cu, Pb, Cl- and SO42-. Especially bottom ash from Amsterdam incinerator contained 1.5% of aluminum and 1000ppm precious metals, which was a potential resource of non-ferrous metals smelting industry. A wet physical separation process was proposed to recover aluminum from MSWI bottom ash with the improved performance than the existing dry separation process. Meanwhile, the combustion tests of the spent aluminum cans and foils and small WEEE showed that the particle size distribution of aluminum alloys during combustion was heavily depending on their wall thickness, and precious metals of small WEEE mainly ended up in 0-2mm fraction of bottom ash.Co-combustion tests of the specific wastes indicated that enrichments and leachiabilties of heavy metals (Cu, Zn, Pb, Mn and Mo) and Cl in the resulting bottom ash were, to different extents, linking with the addition of the specific wastes, including WEEE, shredder fluff, sewage sludge, and plastics waste. Cl and S load also gave a great influence on the emissions of some heavy metals, while water content of the input waste showed a fairly limited effect on the emission of heavy metals. It was found that heavy metals tended to end up into smaller particle size fractions of the ashes. The experimental results observed were in good agreement with thermodynamic calculations using FactSage software with the exception of lower Pb content partitioning into bottom ash through the theoretical calculation. In general, the selected specific wastes could be used as a good indicator for predicting heavy metals and chloride leaching, and thus must be monitored before incineration. The results presented in this thesis would aid environmental authorities in making decisions regarding MSWI bottom ash management and provide useful information of controlling the ash and controlling the partitioning of chlorine and heavy metals for incineration plants of MSW in China.