Regeneration of Activated Carbon Used for Sewage Treatment

Abstract

The treatment of sewage with granular activated carbon is a promising method for the recovery of water. The most suitable conditions for regeneration of carbons used for the clarification of sewage after activated sludge treatment was investigated. The carbon samples used for the sewage treatment in the conditions of Table 1 were heated with a thermobalance (Fig.1) in an atmosphere of nitrogen mixed with 0-10% oxygen. The adsorption properties of the regenerated carbons were compared with the virgin carbons in terms of the adsorption rates and isotherms of methylene blue or sodium dodecylbenzenesulfonate. The weight of the carbons used for the sewage treatment decreased rapidly at 100°C to 550°C in compliance with the desorption of the contaminants (Fig. 2). The adsorption properties of the regenerated carbons, which were heated in nitrogen for 10 min. at a constant temperature in the range from 200°C to 600°C, are compared with the virgin carbons (Fig. 3-5). Those of the regenerated carbons heated above 550°C were equal to the virgin carbons. The con-taminants desorbed equally in pure nitrogen and in nitrogen containing oxygen, but the activated carbons were decomposed by the oxidation above 400°C in the atmosphere of nitrogen containing oxygen (Fig. 6). The rates of this decomposition are expressed by the next equation, d Wt/dt=kWt(02)n where Wt is weight of carbon at time t. The decomposition rates of the carbons used for the sewage treatment were faster than the virgin carbons (Fig 7-9). The effect of the oxygen concentration on the decomposition rates of the carbons used for the sewage treatment was smaller than the virgin carbons (Fig. 10-42), but the activation energies of the decomposition reaction showed only a slight difference (Fig. 13). The oxygen concen- tration had little effect on the adsorption properties of the regenerated carbons (Table 3).