Biotransformation of Estrogens in Nitrifying Activated Sludge Under Aerobic and Alternating Anoxic/Aerobic Conditions

Abstract

Natural and synthetic estrogens present in municipal wastewater can be biodegraded during treatment, particularly in activated sludge. The objective was to assess the extent of transformation of 17‐β‐estradiol (E2) and 17‐α‐ethinylestradiol (EE2) by nitrifying activated sludge and evaluate potential relationships between availability of oxygen, nitrification rate, and estrogen removal. For each batch experiment, two reactors were set up—aerobic and alternating anoxic/aerobic—which were then amended with E2 and EE2 from methanolic stock solutions. The EE2 was persistent under anoxic conditions; under aerobic conditions, the observed level of its removal was 22%. The E2 was readily converted to estrone (E1)—faster under aerobic (nitrifying) than anoxic (denitrifying) conditions. During the initial anoxic conditions, a metabolite consistent with 17‐α‐estradiol transiently accumulated and was subsequently removed when the reactor was aerated. Higher removal rates of estrogens were associated with higher nitrification rates, which supports the contention that the nitrifying biomass was responsible for their removal.

Assessment of the removal of estrogenicity in biological nutrient removal wastewater treatment processes

“…The ratio of the degradation efficiencies in the aerobic, anoxic and anaerobic zones for both pilot and bench scale BNR process were 8:2:1 and 11:5:1 respectively. The observed high degradation efficiencies in the aerobic zones of the pilot and the bench scale BNR process was consistent with previous studies that reported high degradation of EDCs as monitored by chemical concentrations (Joss et al, 2004;Dytczak et al, 2008). Thus, the results suggest that high reductions of estrogenicity can occur under aerobic conditions in BNR processes.…”

“…can occur under both aerobic and anoxic conditions (Ternes et al, 1999;Shi et al, 2004;Dytczak et al, 2008). This transformation reaction has also been previously reported to be rapid and usually occur early in batch experiments (Onda et al, 2003).…”

“…Since the YES assay technique was employed to describe the behavior of E1 and E2 in the batch tests it was necessary to address the degradation of E2 to E1, which is also an estrogenic compound, and the subsequent degradation of E1 (Ternes et al, 1999;Shi et al, 2004;Dytczak et al, 2008;Hashimoto and Murakami, 2009) in the modeling (Eq. (2)).…”

“…Previous studies that have investigated the biodegradation of EDCs in activated sludge systems have monitored the disappearance of the compounds using chemical techniques without an understanding of the estrogenicity associated with the disappearance of the compounds (Joss et al, 2004;Dytczak et al, 2008). However, it has been demonstrated in other process configurations that the disappearance of estrogenic compounds does not necessarily eliminate estrogenicity.…”

“…For example, the transformation of 17β-estradiol (E2) in activated sludge processes was reported to involve E2 oxidation to estrone (E1), another estrogenic compound (Ternes et al, 1999;Shi et al, 2004;Dytczak et al, 2008). There is the potential for differing conversions between estrogenic compounds in different redox conditions (Joss et al, 2004;Czajka and Londry, 2006;Dytczak et al, 2008). Hence, bioassays are important tools for characterizing the impact of redox conditions on the fate of estrogenicity in BNR processes.…”