RESPONSE SURFACE METHODOLOGY AS OPTIMIZATION TOOL IN STUDY OF COMPETITIVE EFFECT OF Ca2+ AND Mg2+ IONS IN SORPTION PROCESS OF Co2+ BY DRIED ACTIVATED SLUDGE

The aim of present study was to investigate biosorption of cobalt ions onto dried activated sludge (DAS) from ternary solution Co-Ca-Mg, as a function of pH and concentration of cobalt, calcium and magnesium via Box-Behnken design under Response surface methodology (RSM). The four parameters namely cobalt initial concentration of 2000 μmol/L, calcium initial concentration of 2000 μmol/L, magnesium initial concentration of 2000 μmol/L and pH of 5.5 were chosen as center points from the previous study of metal sorption process. The experimental data on sorption capacity Qexp of DAS for Co2+ ions were obtained by 60Co gamaspectrometry and fitted into a quadratic polynomial model using multiple regression analysis. The experimental Box-Behnken design revealed that biosorption of cobalt ions from ternary system increase with increasing pH of the system, initial cobalt concentration and magnesium concentration. Results showed also drastic inhibitory effect of increasing calcium concentration in sorption process of cobalt ions. The present study provides valuable information about combined effect of independent variables on sorption process from multivariable system and enables us to minimize number of needed experiments from 60 to 29.