Removal of textile dyestufes from wastewater by adsorptive biodegradation

Removal of dyestuffs from a synthetic wastewater by adsorptive biodegradation was investigated in this study. The dyestuff adsorption capacities of granular, powdered activated carbon (GAC and PAC) and low-cost adsorbents such as zeolite, wood chips and wood ash were evaluated in order to obtain a low-cost adsorbent for use in an activated sludge unit. Then various activated sludge cultures were tested for biodegradation of a selected dyestuff. An activated sludge unit with the selected activated sludge culture and adsorbent was operated at different sludge ages for removal of the dyestuff. Synthetic wastewater containing dyestuff was prepared by dissolving Direct Yellow FGR-U 200%, a widely used dyestuff in the textile industry, in distilled water. In batch adsorption experiments performed in a gyratory shaker, the adsorption capacity of wood ash was found to be comparable with that obtained by powdered activated carbon. Pak-Maya-activated sludge culture was found to be the most suitable activated sludge type among various types tested for removal of the dyestuff. Adsorption isotherms obtained from batch experiments were described by Langmuir isotherms, and adsorption constants (K and xmax) were determined for wood ash. Operation of activated sludge unit with the addition of wood ash at different sludge ages (θc = 3-30 days) resulted in maximum decolorization efficiency of E = 37% at a sludge age of θc = 20 day.