Preliminary tests of sorption properties of thermally transformed activated sludge

Study was conducted in order to check sorption properties of activated sludge which has undergone thermal transformation. For this purpose, anaerobically digested and dewatered activated sludge was dried at 105 C to constant weight. Next this sludge was milled to a particle with a diameter of 0.5–1.0 mm and subjected to thermal activation in a muffle furnace at 600 C. In this way obtained a powder activated carbon based on activated sludge (so called SAC – “sludge-based activated carbon”). Studies of static sorption of two dyes (Lissamine Scarlet 4R and Rhodamine B) were conducted for activated carbon prepared as described above. The reaction pH was 2.5 and 7.0 respectively for the dye Lissamine Scarlet 4R and Rhodamine B. During the tests for both dyes a sorption kinetics (for two different values of the ratio of dye weight and SAC weight) were made. Then, for a predetermined time sorption (selected based on the results of the kinetics) sorption isotherms were made for both dyes. Studies have shown that the dye Rhodamine B was well sorbed by activated carbon produced from activated sludge. In the case of Rhodamine B in order to achieve an effective level of removal of that dye it was required only 0.5 hours of contact time. However, in the case of Lissamine Scarlet 4R it required a much longer contact time. That was required two hours of contact time to achieve a relatively high reduction of concentration of this dye. Also, the results obtained during determining the sorption isotherms of these two dyes, have confirmed that conclusion. The adsorbed charge of Rhodamine B per gram of SAC was significantly higher than the adsorbed charge of the second dye. These differences may have been due to the size of the pores of generated SAC. On the basis of sorption of these two dyes can be supposed, that the SAC was characterized by a pore smaller than the size of molecules of Lissamine Scarlet 4R. Therefore, the sorption process of that dye was limited. In contrast, molecules of Rhodamine B, which are smaller than the molecules of Lissamine Scarlet 4R, were much better adsorbed by the SAC. Additionally, it can be supposed that the surface charge of the generated SAC was negative, because the cationic dye (Rhodamine B) was better adsorbed by this sorbent.