Biodegradation of progesterone and norgestrel in wastewater by functional bacterial gels: Perspectives from simultaneous reduction of transformation products and endocrine disrupting effects

The steroidal progestogens have attracted much attention on their occurrence and fate in wastewater due to their endocrine disrupting effects to aquatic organisms at ng/L levels. Enhanced removal of progestogens by functional bacteria is an environmental-friendly and low-cost technology. However, the effectiveness of the immobilized functional bacteria in simultaneously removing target progestogens, their transformation products (TPs) and endocrine-disrupting risks in wastewater has not been well documented. This study isolated three strains of functional bacteria that can effectively degrade two typical progestogens, progesterone (P4) and norgestrel (NGT), immobilized the bacteria into bacterial gels and constructed the bacterial gels reactor (BGR). Batch experiment showed that the biodegradation of P4 and NGT by the bacterial gels followed first-order kinetics, with kinetic constants of 0.09 and 0.08 h⁻¹, respectively, and 11 and 12 TPs of P4 and NGT were identified by using high resolution mass spectrometry. The BGR was effective in removing P4 and NGT in long-time operating, with removal efficiencies of 99.3 % and 97.1 %, respectively. Further, the BGR was connected in series behind an A/A/O reactor. The long-time operating results showed that the BGR further enhanced P4 (62 %) and NGT (50 %) removal in the A/A/O secondary effluent, with simultaneously reducing the adverse effects of the effluent on transcripts of the zebrafish gonads. Additionally, relative abundances of most TPs were also reduced by the BGR. This study demonstrated the effectiveness of bacterial gels in simultaneously removing P4/NGT, TPs and endocrine disrupting risks in wastewater.