Endocrine disrupting chemicals such as steroid estrogens and alkylphenol
polyethoxylates entering the environment via regular domestic or industrial
discharges have been demonstrated to cause feminization of aquatic organisms at
trace levels. The presence of these compounds in surface waters has been primarily
attributed to their incomplete removal in sewage treatment works and to degradation
products generated from alkylphenolic compounds such as alkylphenols and short
chain one to three ethoxy units, ethoxylates.
This study investigates the factors controlling biodegradation of these chemicals in
four sewage treatment works with various configurations of the biological treatment
stage. Analytical methodologies for these endocrine disrupting compounds have been
developed to allow accurate quantification at nanogram per litre concentrations in
sewage matrices. Three activated sludge plants and one trickling filter work were
examined.
Temperature variation (±10°C) has no impact on the removal of estrogens with the
exception of the conjugated estrone-3-sulphate. Removal efficiencies for most of
these compounds were >90% at most of these works however the biochemical activity
of the biomass was found to be 50-60% more efficient in the nitrifying/denitrifying
plant (STW2) compared to the biological nutrient removal plant (STW3). The
presence of an anaerobic zone in STW3 did not provide additional benefit in the
removal of these compounds compared to a conventional nitrifying/denitrifying plant.
The biochemical activity in the nitrifying only pilot-scale plant (STW4) was in
between that of the nitrifying/denitrifying plant (STW2) and the biological nutrient
removal plant (STW3).
It was found that most of the alkylphenols in the final effluents did not exceed and
complied with the proposed predicted no effect concentration (PNEC) values of 330
ng l-1 and 122 ng l-1 for nonylphenol and octylphenol respectively. However,
concentrations of estrogens at all the works potentially fail to comply with the
proposed Environment Agency PNEC value (E2 equivalent = 1 ng l-1).