Transformations of di-

n

-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) have been investigated in anaerobic/anoxic/oxic (A/A/O) leachate treatment processes. Although the DBP removal processes are different when the DBP initial concentration is different

the overall system DBP removal efficiencies are high (94%). DEHP is much more difficult to remove than DBP. The removal efficiency of DEHP is approximately 75%-78%. The results of mass balance calculations indicate that approximately 33.7%-50.7% of the DBP is degraded by the activated sludge

48.9%-64.9% accumulates in the system

and 0.4%-1.4% is contained in the final effluent. Approximately 15.0%-19.0% of the DEHP is degraded by activated microcosms

75.8%-79.0% accumulates in the system

and 5.2%-6.0% is contained in the final effluent. Biodegradation and adsorption to the activated sludge are the main mechanisms for DBP removal and adsorption to the activated sludge is the main mechanism for DEHP removal. The different removal mechanisms of the two PAEs may be related to their different molecular structures. However

PAEs are not really removed when they adsorb onto the sludge. Therefore

methods for decreasing PAEs adsorp

tion and increasing the biodegradation efficiencies of the leachate treatment processes should be further investigated.