The sorption capacity of long-time aerated activated sludge demonstrated with 2,6-dimethylphenol

The aim of this study was to evaluate the influence of the duration of activated sludge aeration on sorption capacity of the sludge for the hazardous substance 2,6-dimethylphenol (DMP). DMP was not degraded by normal activated sludge of a pilot scale treatment plant for municipal wastewater as shown by BOD measurements. Sludge aeration was performed for up to 50 days. In sorption assays the mixed liquor suspensions aerated for different times were added to solutions of DMP (10 to 50 mg/l) in tap water in order to give biomass concentrations of 1 g MLSS/l in the sorption assay. Also a sorption isotherm with different concentrations of activated sludge aerated for 50 days with a constant initial DMP concentration was recorded. In the experiments solid phase DMP concentrations of up to 20.9 mg DMP/g MLSS were found depending on aeration time of the activated sludge. Sorption equilibria were reached within short periods (about 10 min). DMP sorption capacity of activated sludge reached a maximum on the 43rd day of aeration and decreased afterwards. But the sorption capacity of sludge aerated for 43 days was significantly lower (about 40 % removal of DMP at 1 g MLSS/l from an aqueous solution containing about 50 mg DMP/l) than the adsorption capacity of activated carbon (100 % removal of DMP at 1 g activated carbon/l). On the other hand, activated sludge which had been aerated for an optimum period represents a rather good and cheap sorbent for the refractory DMP, considering the low specific surface of activated sludge compared to the specific surface of activated carbon. However, an appropriate method for removal of the sludge loaded with DMP has to be chosen in order to protect the environment against spreading of the hazardous compound DMP. A multistage biosorption process for DMP removal from industrial wastewater is suggested. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.