Rice Husk Based Adsorbents for Textile Effluent Treatment

Adsorption of textile dyes onto rice husk based adsorbents from aqueous solutions was studied to enable comparison with alternative commonly available absorbents. Batch experiments were conducted to determine the effect of method of treatment of rice husk on adsorption. Untreated and treated rice husk were tested for adsorption of Basic Green 4 and Acid Blue 80. The maximum adsorption was observed at solution pH values above 6 for Basic Green 4 and below 3 for Acid blue 80. Raw rice husk (RRH), base treated rice husk (BRH) and thermally treated rice husk (TRH) were superior to other adsorbents tested. Fixed bed column studies were conducted for RRH, BRH and TRH and breakthrough curves were obtained. Bed capacity, breakthrough time, length of the unused bed and time required for full bed exhaustion under ideal condition were calculated from breakthrough curves. Bed capacities for Basic Green 4 and Acid Blue 80 for thermally treated rice husk were 45 and 30 mg/ g respectively. Experimental data obtained from unsteady state fixed bed column studies were used for scale-up calculations and for determination of industrial scale fixed bed adsorber dimensions. Tests on real textile waste water consisting of a mixture of dyes showed that Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) levels can be reduced to 210 and 30 respectively using thermally treated rice husk.