Optimization Study On The Degradation Of PCDD/Fs In Fly Ash By Hydrothermal Treatment

With the increasing amount of municipal solid waste incineration (MSWI), secondary contamination from incineration has aroused the concern of our society. Heavy metals and persistent organic pollutants (POPs), which contains large amounts of highly toxic substances—PCDD/Fs, are enriched in MSWI fly ash, so it has been classified as a hazardous waste. Therefore, MSWI fly ash must be treated before disposal in landfills, or secondary utilization. The dissertation is funded by national basic research program of China, and launches a series of fundamental experiment of the hydrothermal-fenton treatment. The objectives of the current research involved as follows:1) In order to get a comprehensive study about degradation of dioxins of temperature, hydrogen peroxide, iron ions and pH in fly in the hydrothermal-fenton treatment, the dissertation used a new test design method, which is the orthogonal array designs, to design the16sets of experimental conditions. The new method has saved the human and material resource.2) After hydrothermal reaction fly ash sample mass loss of nearly60%, so the dioxins is "concentrated" in the fly ash. By hydrothermal reaction the alkaline environment can fix heavy metals in fly ash, and there have minimal weight loss in an alkaline environment. Acidic conditions easily dissolved heavy metals into solution, so there have maximum weight loss.3) The results indicate that there are no difference of PCDD/Fs’ degradation under conditions of oxygen and hydrogen, with on catalyst. when pH value is equal to7, this system has optimal degradation efficiency of PCDD/Fs; hydrodechlorination reactions is not the degradation reaction of PCDFs, but it is the major way of PCDDs to degrade.4) It is proved by using range analysis that pH and temperature are significant factors affecting the degradation efficiency of dioxins in the reaction system. In order to achieve better degradation effect, we can precisely control the pH and temperature to achieve the goal, and ignores the iron ions and hydrogen peroxide concentration on the system, reducing costs.Overall, the rational use of orthogonal array design can reduce the test time and cost. Using this design method, the dissertation makes complete the experimental study of hydrothermal degradation of dioxins in fly ash in limited time. There has the optimal conditions obtained by orthogonal array designs. This lay a foundation for industrial application.