Active heterotrophic biomass and sludge retention time (SRT) as determining factors for biodegradation kinetics of pharmaceuticals in activated sludge

The present study investigates the biodegradation of pharmaceutically active compounds (PhACs) by active biomass in activated sludge. Active heterotrophs (Xbh) which are known to govern COD removal are suggested as a determining factor for biological PhAC removal as well. Biodegradation kinetics of five polar PhACs were determined in activated sludge of two wastewater treatment plants which differed in size, layout and sludge retention time (SRT).Results showed that active fractions of the total suspended solids (TSS) differed significantly between the two sludges, indicating that TSS does not reveal information about heterotrophic activity. Furthermore, PhAC removal was significantly faster in the presence of high numbers of heterotrophs and a low SRT. Pseudo first-order kinetics were modified to include Xbh and used to describe decreasing PhAC elimination with increasing SRT.

► Respirometry was used to estimate the amount of active heterotrophic biomass.
► The fractions of active heterotrophic biomass varied strongly between sludges.
► Faster pharmaceutical removal was observed at low sludge retention times.
► Total suspended solids do not reveal information about heterotrophic activity.
► Modified pseudo first-order kinetics was proposed to describe xenobiotic removal as a function of the SRT.