Removal of steroid estrogens in carbonaceous and nitrifying activated sludge processes

Abstract

A carbonaceous (heterotrophic) activated sludge process (ASP), nitrifying ASP and a nitrifying/denitrifying ASP have been studied to examine the role of process type in steroid estrogen removal. Biodegradation efficiencies for total steroid estrogens (Σ EST ) of 80 and 91% were recorded for the nitrifying/denitrifying ASP and nitrifying ASP respectively. Total estrogen biodegradation (Σ EST ) was only 51% at the carbonaceous ASP, however, the extent of biodegradation in the absence of nitrification clearly indicates the important role of heterotrophs in steroid estrogen removal. The low removal efficiency did not correlate with biomass activity for which the ASP carbonaceous recorded 80 μg kg −1 biomass d −1 compared to 61 and 15 μg kg −1 biomass d −1 at the ASP nitrifying and ASP nitrifying/denitrifying respectively. This finding was explained by a moderate correlation ( r 2 = 0.55) between total estrogen loading (Σ EST mg m −3 d −1) and biomass activity (μg Σ EST degraded kg −1 d −1) and has established the impact of loading on steroid estrogen removal at full-scale. At higher solids retention time (SRT), steroid estrogen biodegradation of >80% was observed, as has previously been reported. It is postulated that hydraulic retention time (HRT) is as important as SRT as this governs both reaction time and loading. This observation is based on the high specific estrogen activity determined at the ASP carbonaceous plant, the significance of estrogen loading and the positive linear correlation between SRT and HRT.