Sewage sludge inevitably contains a wide range of trace organic contaminants, particularly those that are relatively hydrophobic. The objective of this research was to evaluate the combined effects of sequential anaerobic/aerobic digestion on residual trace organics, concentrating on chemicals that are responsible for observed estrogenic/androgenic activity in biosolids. Full-scale sequential digestion was simulated using bench-scale bioreactors in which the primary independent variables were retention time, temperature, and oxygen loading during aerobic digestion.  Sludge solids were extracted via microwave assisted extraction, and estrogenic/androgenic activities were then measured using the Yeast Estrogen/Androgen Screens (YES/YAS bioassays). The concentrations of EDCs such as nonylphenol, octylphenol and their parent compounds (alkylphenol polyethoxylates, APnEOs) were analyzed by gas chromatography�mass spectrometry. Also solid phase extracts were fractionated using a 30-minute gradient HPLC system and collected at 1-min intervals from C18 column with increasing solvent concentrations. The fractionated estrogenic/androgenic activities were screened using YES and YAS bioassays. Estrogenic and androgenic fractions were analyzed to determine responsible compounds.  Results included treatment-dependent changes in estrogenic and androgenic activities. Standard mesophilic anaerobic digestion increased the total estrogenic and androgenic activities of sludge. The effectiveness of aerobic treatment was directly related to hydraulic detention time and oxygen loading rate. Furthermore, the thermophilic (55o C) aerobic digestion was much more effective at reducing estrogenic and androgenic activities, even at relatively short detention times (5 and 10 days). Doubling the airflow rate from 0.5 L/min to 1.0 L/min at the 5-day retention time further improved reactor performance. Results suggest that conventional sludge treatment processes can be designed and operated to better remove estrogenic activity in sludge. This is particularly important when digested sludge is utilized as a soil amendment.

Fate of estrogenic/androgenic activity and estrogen/androgen mimics   during sludge digestion

243rd National Meeting (2012)

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