Degradation rate constants of steroids in sewage treatment works and receiving water.

Steroid estrogens are one of the most important groups of endocrine disrupting chemicals (EDCs) which can cause adverse effects on wildlife species and humans. Natural estrogens, including estrone (E1) and estradiol (E2), and synthetic estrogen 17alpha-ethinylestradiol (EE2) together contribute to most of the estrogenic activity in sewage effluents and receiving water. Degradation, particularly aerobic biodegradation was found to be the dominant removal mechanism in these environments. There are a number of factors such as temperature, pH, SRT, HRT and biomass concentration that can affect the rate of biodegradation. This paper reports the results of investigations in to the relationship between the equivalent biomass concentration and degradation rate constants for compounds E1, E2 and EE2 in various environments. It was found that a higher biomass concentration leads to higher rate constants, and relatively good linear correlations (R2 =0.73, 0.79 and 0.73) between the logarithm of the rate constants and the corresponding logarithm equivalent biomass concentration (EBC) values were obtained.