Microwave-assisted Acid Degradation Treatment of MSWI Fly Ash

Autor: Chien-Chung Liu, 劉建中
Rok vydání: 2013
Druh dokumentu: 學位論文 ; thesis
Popis: 101
The refuse disposal strategy of Taiwan has adoped incineration as the primary method of treatment with landfills as supplement. Fly ash discharged from municipal solid waste incinerators (MSWI) was classified as hazardous waste because the leashing of heavy metals (especially Pb) and the content of PCDDS/FS are usually over the regulation limits, so it was majorly treated by Solidifition/Stabilization method, after that sent to the landfills for final disposal. Such way will caused the serious loading of limited landfills capacity and also affected the implementation of Zero Waste Policy. This study fouced on using the microwave-assisted acid degradation treatment (MDT) to reduce the hazardous materials (Pb and PCDDS/FS) simultaneously. The fly ash after MDT will be harmless and easily be resused. Microwave-assisted acid degradation treatment has the advantages of uniform heating, quick reaction, low power consumption and effect reduction of hazardous materials. The fly ash (FA) and reaction ash (RA) used in this study were sampled separately from a domestic large-scale MSWI in northern Taiwan. They were tested by physical and chemical properties but only the RA was used for MDT test. The MDT method usesd an acid combination of H2SO4 (17.8M) for its high boling point and HNO3 (15.6M) for strong oxidation power, and tested with different reaction time and temperature in the same conditions of solid/liquid ratio (1/10) and 600W. It is found that the TCLP-extractable concentration of Pb will decrease with the increases of both treatment time and temperature, especially the reduction efficiency is significant in the early time of reaction. In the case of treatment temperature of 433°K, the reduction efficiency can reach 98.5％ after treatment time of 16 minutes. It is equivalent to the TCLP-extractable lead concentration of 46.2 mg/L in raw fly ash is down less than 0.69 mg/L, which is very lower than the hazardous regulation limit in Taiwan (5.0 mg/L). This work took the experimental data for correlation, and obtained the correlation equation between reduction efficiency and treatment time and temperature with a square correlation coefficient of 0.9401 as following: η(%)= 1-exp〔-30‧t‧exp (-2,210/T)〕. This equation can be used to estimate the reduction efficiency (η) for different temperature and time by the MDT in order to choose the effective operating conditions that make sure the fly ash after treatment is below the legal limits. The toxic equivalent concentration of PCDDS/FS has dropped to 0.00047 ng-I-TEQ/gdw (reduction efficiency is 99.94%) after MDT with the same test conditions above but higher solid/liquid ratio (1/20), which means that the MDT also get good reduction efficiency for PCDDS/FS in fly ash. In this study, on the basis of 100 tons / day for MDT plant scale, with a subsequent two-stage washing units, the treatment cost is 6,877 NTD / ton. The fee is higher than solidifition method (3,758 NTD / ton) and two-stage water washing method (3,939 NTD / ton), but lower than the melting technology (10,049 NTD / ton). The most important advantage of MDT is that the major hazardous substances of heavy metals and PCDDS/FS in fly ash could be reduced effectively so that the fly ash after treatment will be harmless and beneficial for recycling and utilization. It is worthing on the follow-up application.
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