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Effect of microwave hydrolysis on transformation of steroidal hormones during anaerobic digestion of municipal sludge cake Hamid, Hanna


This research evaluates the fate of 16 steroidal (estrogenic, androgenic and progestogenic) hormones during advanced anaerobic digestion of municipal sludge cake generated at the Kelowna’s wastewater treatment plant using microwave (MW) pretreatment. Effect of sludge pretreatment temperature (80, 120, 160℃), digester operating temperature (mesophilic at 35 ± 2℃, thermophilic at 55 ± 2℃) and sludge retention time (SRT: 20, 10, 5 days) were studied employing eight lab-scale semi-continuously fed digesters. To determine the potential effect of MW hydrolysis, hormones were quantified in sludge (total) and supernatant (soluble) phases of the digester influent and effluent streams. Seven of 16 hormones were above reporting limit (RL) in one or more of the samples. Hormone concentrations upto 1,640 ng/L and 2491 ng/g (for androstenedione, (Ad)), respectively, were detected in soluble and total phases of the influents. Microwave hydrolysis resulted in both release and attenuation of hormones in the soluble phase. High accumulations (upto 30 times for androstenedione (Ad) of the influent concentration) of hormones observed in the effluents of un-pretreated (control) digesters suggested that anaerobic digestion was inefficient to remove these compounds. Simultaneous accumulation and removal of 17β-estradiol (E2) and estrone (E1) as well as progesterone (Pr) and androstenedione (Ad) indicated possible transformations among the hormones. At a 20-day SRT, thermophilic digesters contained overall less concentration of steroidal hormones in their digestate supernatants to be recycled to the beginning of the treatment plant. However, mesophilic digesters seemed to perform better in terms of total decrease of hormones and would likely to have lower concentrations in their dewatered digestates to be disposed of via land application at same SRT (20 days). Microwave pretreatment increased total chemical oxygen demand (TCOD) volatile solids (VS) removals and methane production compared to un-pretreated (control) digesters. However, improvements were more prominent at the shortest SRT of 5 days.

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