Abstract:
Removal of lignin and tannin by wasted powdered activated carbon as used ballasting agent from AS process was studied by comparing with five adsorbents; powdered activated carbon (PAC), powdered activated carbon as used ballasting agent (PACB), digested powdered activated carbon as used ballasting agent (PACB-Di), sludge(S) and digested sludge (S-Di). Batch experiments were conducted for studying the adsorption kinetics and isotherms of lignin and tannin, including effects of pH. Physical characterization of adsorbents obtained by thermogravimetric ananlysis (TGA) indicated approximately 25% (w/w) of microorganism on PACB. Equilibrium adsorption state of lignin by PAC, PACB and PACB-Di can be reached faster than S and S-Di as 1 and 20 hours, respectively. And adsorption kinetics of tannin showed that adsorption of PAC, PACB and PACB-Di can be reached the equilibrium state faster than the S and S-Di as 2 and 6 hours, respectively. The results showed that the all adsorption kinetics and isotherms of lignin and tannin could be fitted to pseudo-second order and Freundlich isotherm model. The obtained results indicated that PACB and PACB-Di had higher adsorption capacities of lignin and tannin comparing with S and S-Di, however, virgin PAC performed highest adsorption capacities of lignin and tannin. Sludge digestion processes did not affect to adsorption capacities of lignin and tannin. Increase of pH higher than pHPZC could a little bit enhance lignin adsorption capacities of PAC PACB and PACB-Di, but did not affect to S and S-Di significantly. Moreover, it was found that adsorption capacities of tannin did not related to electrostatic interaction.