Experimental design to optimize preparation of activated carbons for use in water treatment

A series of seven activated carbons was obtained for use in drinking water treatments by steam activation of olive waste cakes This raw material is an abundant and cheap waste byproduct of oil production making these activated carbons economically feasible The activated carbons prepared by the one step method were characterized and the evolution of their characteristics (yield adsorption capacities and porosity) was analyzed as a function of the experimental parameters (activation temperature and activation time) using the Doehlert matrix The Doehlert matrix allows the response surface to be studied with a good quality parameter estimation of the quadratic model Each response has been described by a second order model that was adequate to predict responses in all experimental regions The coefficients of the postulated model were calculated from the experimental responses by means of least squares regression using the NEMROD software We determined the region in which the optimum values of both activation temperature and activation time were achieved for the preparation of activated carbons suitable for use in water treatments The optimal activated carbon was experimentally obtained and its characteristic parameters showed a good agreement with those calculated from the model The results obtained for activated carbons prepared by the one step method were compared with those for activated carbons prepared by the two step method The characteristics of activated carbons obtained by the one step and two step methods showed that one step activated carbons have a highly developed porous texture formed mainly of large macropores and micropores whereas two step activated carbons have a predominance of mesopores and narrow micropores These activated carbons from olive waste cakes showed a high capacity to adsorb herbicides (24 dichlorophenoxyacetic acid 24 D and 2 methyl 4 chlo rophenoxyacetic acid MCPA) from water with adsorption capacity values higher than those corresponding to a commercial activated carbon used from drinking water treatments.