Theromdynamics of Steroid Estrogen Sorption to Activated Sludge

Abstract

Sorption is an important mechanism for removal of 17a-ethinylestradiol (EE2) in biological wastewater treatment. In an effort to deepen our understanding of this process, this work investigated the underlying thermodynamic parameters. Biomass was harvested from a membrane bioreactor (MBR) and a sequencing batch reactor (SBR), and sorption experiments were conducted over a range of temperatures. Sorption of EE2 to activated sludge was spontaneous (?G values were between -16 and -11 KJ/mol), enthalpy-driven (?H values were -37 KJ/mol (MBR) and -48 KJ/mol (SBR)), and entropy-retarded (?S values were -74 (MBR) and -119 J/mol/K (SBR)). Although EE2 is nonpolar, hydrophobic interactions were not dominant driving forces. The thermodynamic data also suggested that EE2 sorption to biomass was primarily physisorption, but it also included low level chemisorption. The FT-IR results suggested that chemical reactions were not significant enough to shift the detectable chemical bonding characteristics of the biomass functional groups.