This paper investigates the factors determining element behavior in municipal solid waste incinerators. The method is based primarily on field measurements in full-scale incinerators. Material flow analyses are carried out in an incinerator. The main focus is placed on the processes in the furnace. The following master variables determine element transfer behavior to the raw gas in the furnace: (i) occurrence and distribution of the elements in the input waste; (ii) temperature, redox conditions, and content of chlorine and of reaction partners other than oxygen and chlorine in the furnace bed; and (iii) residence time and mixing conditions in the furnace bed. Twenty-nine elements are divided into two groups with respect to their transfer behavior to the raw gas and to the bottom ash in the furnace. The results indicate that the elements Si, Fe, Co, Cr, Mn, Ni, P, Al, Ca, Mg, Na, Ba, Li, Ti, and K are transferred mainly to the raw gas by entrainment. Occurrence and distribution of these elements in the input waste determine primarily their transfer coefficients. Evaporation is the main transfer process for the remaining investigated elements to the raw gas. In addition to the occurrence and distribution of the elements in the input waste, physical and chemical conditions as well as kinetics are the main factors responsible for the different transfer behaviors between the elements F, Cu, Mo, Pb, Sn, Zn, Br, Sb, C, S, Cl, As, Cd, and Hg.

Laboratory experiments with synthetic samples are conducted to obtain information on the evaporation behavior of metals in incinerators. In combining the results obtained through field measurements presented in a companion paper in this issue, hypotheses are postulated on the influence of physical and chemical conditions as well as of kinetics on the evaporation behavior of the chosen elements in the furnace bed. These are validated by thermal treatment of bottom ash samples in the laboratory. A temperature increase of from 500 °C to 900 °C causes higher transfers of most metals into the gaseous phase. Mo and Sb are the exceptions. Chlorine availability generally favors evaporation. Increasing oxidative conditions cause lower Sn transfers. Transfer of the elements Cd, Mo, Sb, Sn, and Zn is negatively affected by their reaction with reaction partners other than oxygen and chlorine occurring in municipal solid waste. Oxidation of organic carbon to CO and CO2 as well as HCl formation determine the distribution of temperature, redox conditions, and chlorine availability in the furnace bed. First indications are obtained on the residence times of goods under these different local conditions. The knowledge acquired can be used to design new incinerators with “tailor-made” products that can either be recycled or landfilled without an adverse environmental impact for the long term. For this purpose, mechanical processing techniques, thermal treatments at temperatures between 500 °C and 1100 °C, and high-temperature treatments (>1100 °C) including melting processes will have to be combined.

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Incinerators do not achieve a complete mineralization of organic constituents of municipal solid waste. The solid residues (bottom ash, boiler ash and air pollution control residues) contain carbon which can be determined as total organic carbon (TOC). This work focuses on the TOC composition and its significance to the genesis and diagenesis of the solid residues. An analytical procedure is presented to characterize carbon species by different chemical and microscopic analytical methods. The procedure is based on two steps. In the first step a quantitative classification of TOC into four different carbon species (elemental carbon, water extractable organic carbon, dichloromethane extractable organic carbon and non extractable organic carbon) is performed to obtain a first survey of the TOC composition. Based on this survey a further characterization of individual carbon species is performed. The results of the qualitative and quantitative characterization of carbon species allow to postulate hypotheses on the influence of organic carbon on the long-term behavior of the solid residues.

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A method is presented to predict the short-term (months to years) and long-term (> 30 years) chemical behaviour of bottom ash from municipal solid waste incinerators in monofills. It is based on bottom ash composition and laboratory kinetic studies of bottom ash with water. Bottom ash after the quench tank is a reactive mixture in which slow and fast acid/base reactions occur. These intrinsic acid/base reactions continue for at least several months, and the end point is not yet known. The heavy metal concentrations observed in the aqueous extracts reflect primarily the advance of these reactions. Consequently leaching tests based solely on short-term (hours to months) extraction procedures cannot predict the chemical behaviour of bottom ash in monofills. However, laboratory experiments with samples of bottom ash, in which the intrinsic acid/base reactions have proceeded differently, provide useful information on the nature of chemical reactions significant in the short- and long-term.

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