Hiroyuki Harada*, Hideo Furuta*, Izumi Hirasawa**, Shigeki Nakajima*

*Faculty of Engneering, Kumamoto University
(39-1, Kurokami 2-Chome, Kumamoto 860 Japan)
**Faculty of Engneering, Waseda University

Abstract

Sanitary landfill leachate softening processes have been developed for scaling problems. Calcium carbonate crystallization characteristics were studied by using the apparatus of fluidized-bed type reactor, with the existence of seeds (blast furnace slag) . Caustic soda and sodium hydrogencarbonates were used for softening. The concentration of calcium in synthetic leachate was adjusted from 1.2 to 14.1 mol m-3. The crystallization proceeded rapidly. At the first sampling point (0.1m), the concentration of calcium had already been reduced from its influent value to effluent value. The calcium removal rate reached was 48%-60%. The turbidity of effluent was under 30, and its pH value was 7.6-8.0. The contents of the fluidized-bed are thoroughly mixed. This reaction can be described by the following equation:

Co - C = Ko C T

where Co: influent of Ca2+[mol m-3] C: effluent of Ca2+[mol m-3] T: retention time [h] Ko: reaction rate constant[h-1]

Key words: crystallization, softening, fluidized-bed, blast furnace slag, leachate, landfill