Comparative evaluation of commercial and sewage sludge based activated carbons for the removal of textile dyes from aqueous solutions
Almost every industry uses coloring matter to color their products and the residual and unspent substances are discharged in to the environment, particularly aquatic environment. Discharge of such colored effluents imparts color to the receiving water and interferes with its intended beneficial use. In addition, recent reports suggest that several color-causing substances are micro toxic to the aquatic biota. Moreover if effort is not made to remove this visible pollution, public assumes that little effort is being expanded in removing other pollutants also. It is thus imperative that color must be removed from the effluent before disposal. Among different industrial wastewaters with different types of color causing substances, synthetic textile organic dye color wastes occupy a prominent position. Over 7 x 1 0 tons and approximately 10000 different types of dyes and pigments are produced worldwide annually. It is estimated that 10 to 15% of the dye is lost in the effluent during the dyeing process (Young et at., 1997; Danis et at., 1998). Various physical, chemical, physico-chemical and biochemical chemical processes like sedimentation, equalization, neutralization, flotation, chemical precipitation, coagulation and flocculation, adsorption, ion- exchange, reverse osmosis, electro-chemical coagulation etc., have been investigated for the removal of dyes from aqueous solutions (McKay, 1982; Barton, 1987; Karithikeyan, 1990; karthikeyan, 1988; Venkatamohan, 1997). The stringent and rigid national effluent disposal standards call for an advanced treatment among which liquid-phase adsorption has been found highly efficient for removal of color in terms of initial cost, simplicity of design, ease of operation and insensitivity to toxic substances. Activated carbon is the most widely used adsorbent because it has excellent adsorption efficiency for organic compounds but its use is usually limited due to its high cost (Y. S. Ho et at., 1999; Rozada et at., 2003).