Fate of estrogens in biological treatment of concentrated black water
Sewage treatment plants (STPs) effluents were found to have estrogenic character which is mainly due to the presence of estrone (E1), 17β-estradiol (E2) and 17α-ethynylestradiol (EE2). E1 and E2 are natural hormones excreted by mammals in urine and faeces, whereas EE2 is a synthetic hormone present in the contraceptive pill. The largest part of the estrogens is excreted via urine as glucuronide or sulphate conjugate with no estrogenic properties. These conjugates can be cleaved back to their original form by bacterial enzymes, where deconjugation of glucuronide conjugates is faster than of sulphate conjugates.
Human excreted estrogens are insufficiently removed in conventional treatment systems designed to remove bulk organic matter and nutrients. Maximum reported concentrations in STP effluents are 76 ng/l for E1, 64 ng/l for E2 and 42 ng/l for EE2. Effects on fish were already prevalent at 3.3 ng E1/l, 1 ng E2/l and 0.03 ng EE2/l, values that are often exceeded in surface waters.
Present research focused on the fate of estrogens in sanitation concepts with source separated collection and treatment of domestic wastewater i.e. black water (toilet), grey water (personal hygiene, kitchen) and rain water. Source separated collection offer benefits in terms of energy and resource conservation. By applying vacuum toilets in these concepts, the black water volume containing estrogens is about 7 L per person per day, whereas in conventional sanitation concepts this volume (including rain water) is about 200 L per person per day.
Adsorption and biodegradation are considered the most important processes for the removal of estrogens in biological wastewater treatment systems, and therefore adsorption constants and first order degradation rates were determined. Besides, their fate was investigated in a concentrated black water pilot treatment system consisting of UASB septic tank, with aerobic post-treatment. Determination was established by HPLC with UV, fluorescence and diode array detection and GC-MS for environmental relevant concentrations.
The highest degradation rates were obtained under aerobic redox conditions for all three estrogens, with EE2 being the most persistent as was also confirmed in literature. Increasing sludge retention time had a positive effect on the biological removal rates, whilst nitrifiers did not contribute significantly to it. The results showed that reduced bioavailability, e.g. desorption of adsorbed estrogens, can suppress the conversion rate. During anaerobic conditions, a reduction of E1 to E2 was observed but no decline for the sum of E1 and E2 nor EE2 was observed in various types of sludge.
In the pilot UASB septic tank effluent, total concentrations of 4.02 μg E1/l and 18.69 μg E2/l, of which >70% for E1 and >80% for E2 were in conjugated form. EE2 concentrations were below the detection limit. In the effluent of the post-treatment E1 and E2 were present in concentrations of 1.37±1.45 μg/l and 0.65±0.78 μg/l, respectively. The limited deconjugation of conjugated estrogens during treatment was demonstrated when UASB septic tank was spiked with the sulphate conjugate of E2, revealing that 99% of the detected E2 in the final effluent is in conjugated form.
Even though the application of source separation can prevent storm water overflow and reduce the volume of the wastewater in which estrogens are present, high effluent concentrations after biological treatment necessitate additional treatment. Besides, there is a need for information on the deconjugation rates and the behaviour of conjugated estrogens in general.