Fundamental Study on Nitrogen Removal from Paddy Drainage Using Clinker Ash

抄録

Clinker ash is a kind of coal ash produced by the burning of coal at thermal power plants. Recycling of clinker ash is highly desirable since most of it goes to landfills at present. Because of its porous solid, clinker ash has high potential as a means of purifying contaminated water. On the other hand, nitrogen outflow by paddy drainage has become a major problem in Japan. Therefore, this study examines the effectiveness of a filtering system using clinker ash for removing nitrogen from paddy drainage. A column experiment was conducted in the laboratory to examine the nitrogen removal function of clinker ash. Four types of filtering materials were prepared as the test samples. The Sample I consisted only of clinker ash; the Sample II and the Sample III were a mixture of clinker ash and paddy soil in the ratios of 3:1 and 1:3 respectively; and the Sample IV was comprised of paddy soil only. Each sample was poured into PVC columns (44 mm in diameter; 350 mm in length). A solution prepared with NH₄-N at a concentration of 10 mg/L and C/N of 12 was fed to the columns at a flow rate of 100 to 200 mL/d for 121 days. During the experiment, the columns were kept saturated at a room temperature of 24.4±1.3 °C and illuminated at 544±192 lux. The study showed that clinker ash has the effect of removing nitrogen. However, it also found that clinker ash's removal function is compromised when a large amount of paddy soil is mixed with clinker ash. In order to remove nitrogen from paddy drainage by using clinker ash, only a relatively small amount of paddy soil should be mixed with clinker ash.