Detoxification of PCBs in fly ash from MSW incineration by hydrothermal treatment with composite silicon-aluminum additives and seed induction

Fly ash (FA) produced during municipal solid waste incineration (MSWI) contains hazardous polychlorinated biphenyls (PCBs). Hydrothermal treatment (HT) is a promising technology for the degradation of organic compounds and was used in this study to detoxify PCBs in FA. This study examined the effects of HT reaction temperature, as well as the addition of coal fly ash and diatomite as a composite silicon-aluminum additive and tobermorite seed crystals as an inducer, on the efficiency of PCB detoxification. The percent removal of dioxin like PCBs and of their toxic equivalency both showed a positive correlation with tobermorite content in HT products. We attributed this to an improved Ca/(Si + Al) molar ratio achieved by adding 30% silicon-aluminum additives before HT. The percent removal of PCBs at a reaction temperature of 200 degrees C was higher than at 150 degrees C. Experimental treatments containing added tobermorite seed produced the highest levels of PCB removal, and tobermorite seed addition had a greater influence on PCB detoxification efficiency. The highest percent removal of toxic equivalency of dioxin-like PCBs was 99.8% and was attributed to the improvement in tobermorite purity as achieved by addition of 30% silicon-aluminum additive, 3% seed, and a reaction temperature of 200 degrees C.