Softening treatment of leachate from sanitary-landfill by crystallization process

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(1) Sanitary landfill leachate softening processes have recently gained importance for scaling problem. Calcium carbonate crystallization characteristics were studied by using the apparatus of fluidized-bed type reactor, with the existence of seeds (blast furnace slag). The caustic soda and sodium hydrogen carbonates 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, the concentration of calcium was already 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 7.3-8.0. The contents of the fluidized-bed are thoroughly mixed. This reaction can be described by the following equation :Co-C=Ko・C・rhetawhere Co : influent of Ca^<2+>[mol・m^<-3>] C : effluent of Ca^<2+>[mol・m^<-3>] rheta : retention time [h] Ko : reaction rate constant[h^<-1>](2) Treatment of landfill leachate using a process for softening such leachate by crystallization was studied. Concentrations of human, organic substance and ammonia in the leachate were lowered after this treatment. Centered pellets and molten slags, prepared from sewage sludge, were utilized as seed to recycle such sludge effectively. Experimental treatments were carried out to determine the crystallization rate, and effects of operating conditions on the reaction rate was discussed. The reaction processes following to second order kinetics. The effect of reaction temperature was negligible.The resulting, the total hardness reaction rate was proportional to 0.6th power of pH value.