A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, Asian Instiute of Technology; Inter-University Program on Environmental Toxicology, Technology and Management, Chulabhorn Research Institute and Mahidol University

Thesis (M.Eng.) - Asian Institute of Technology, 2004

Fly ash is a waste product of coal-fired power plants. Fly ash from Mae Moh power plant in Lampang province, northern Thailand was investigated in this study to obtain detailed information on its heavy metals (As, Cd, Hg, Pb and Zn) content and to gain an understanding of leaching potential of these elements associated with its disposal in landfills. The fly ashes from four units of power plant (Unit 6, 8, 10 and 11) were analyzed. Every metal content except mercury is at higher level than the background soil. The average arsenic content was two times higher than the background soil and unit 11 contains the largest amount of arsenic (148.5mg/kg). Mercury content of fly ash in the dumping site is not detectable. Sludge, end product of wastewater treatment plant, from Nong Kaem wastewater treatment plant was also investigated. The average arsenic content was higher in fly ash (89.56mg/kg) than in sludge (22.0lmg/kg) whereas cadmium, lead, zinc and mercury content were higher in sludge (0 .56, 306.07, 1963.23 and 3.97mg/kg, respectively) than in fly ash (0.46, 10.07, 90.73 and Omg/kg, respectively). Fly ash has the leaching potential of heavy metals and this potentiality increases with time for 21 days duration of experiment. But in case of sludge, there is also higher leaching potentiality but it decreases with time. By leaching, the toxic metals may be released into the environment affecting the living organisms. To minimize the effect of these heavy metals on the environment, artificial soil was made by mixing these two kind of toxic wastes with lime at varying ratios. The lowest leaching, the highest plant growth, and minimal uptake of metals by plants, were observed when the fly ash, sludge and limemixing ratio was 3:6:1 (FASAR). The highest total nitrogen (0.881%), available phosphorus (364ppm), potassium (54.12ppm) and organic matter (5.96%) were also observed in the same ratio. To minimize the effect of pH of artificial soil on plants, natural soil was mixed with it at different ratios, i.e. 3: 1, 1: 1 and 1 :3. The best results were found when there was the highest amount of natural soil, i.e. the ratio was 3: 1. This result shows that artificial soil can be used as a soil conditioner to enhance the performance of natural soil. Further detail study will help to optimize the mixing ratio of both natural soil and F ASAR, which will bring benefits to the soil, as well as sound management of waste products from industry.