Influence of Hydraulic Retention Time, Sludge Retention Time, and Ozonation on the Removal of Free and Conjugated Estrogens in Japanese Activated Sludge Treatment Plants

Abstract

This study describes the occurrence, fate,and removal of free estrogens (estrone (E1), 17β‐estradiol (E2), estriol (E3), 17α‐ethynylestradiol (EE2)) and their glucuronide and sulfate conjugates (estrone‐3‐sulphate (E1‐3S), 17β‐estradiol‐3‐sulfate (E2‐3S), estriol‐3‐sulfate (E3‐3S), estrone‐3‐glucuronide (E1‐3G), 17β‐estradiol‐3‐glucuronide (E2‐3G), and estriol‐3‐glucuronide (E3‐3G)) in 12 sewage treatment plants in Japan. Glucuronide conjugates were only rarely detected in sewage influents and entirely eliminated within the treatment plants. E1 was found at 69 ng/L, E2 at 108 ng/L, E1‐3S at 18 ng/L, and E2‐3S at 78 ng/L in the sewage influents. The average removal efficiency for E1, E2, and sulfate conjugates was 88, 92, and 93%, respectively, following activated sludge treatment. The removal of E1 and E2 was improved with increasing the sludge retention time (SRT), with the highest removal typically found from 12 days SRT onward. The removal of sulfate conjugates was also related to SRT with highest removals found from eight days SRT onward. No correlation was found between the hydraulic retention time and the removal of any of the estrogens. The ozone dosage of 4–7 mg/L reduced E3 and E2‐3S and E3‐3S to below detection levels. Overall ozonation reduced the estrogenicity of the effluents as expressed as estradiol equivalents from 8.4 to 0.7 ng/L. The results suggest adequate river basin management of estrogens in Japan could be accomplished by a mixture of activated sludge plants with long SRT and where necessary, the addition of tertiary ozonation.