Biopolymers recovered from waste sludge as carriers for bacteria targeting 17β-Estradiol (E2) degradation

Wastewater treatment plants (WWTPs) are major pathways of contaminants of emerging concern (CECs) release into aquatic environments. Among CECs, 17β-Estradiol (E2) is an endocrine-disrupting compound frequently detected in WWTP effluents and listed as a priority substance under European water policy. Although aerobic granular sludge (AGS) is an effective biological treatment technology, CECs removal is often incomplete and influenced by microbial community composition. Therefore, bioaugmentation with immobilized degrading bacteria may enhance degradation efficiency and process robustness. This study explored the potential of extracellular polymeric substances (EPS) recovered from waste AGS as carriers for Rhodococcus sp. ED55, a specialized E2-degrading bacterium. To this end, EPS were used as immobilization matrix to produce EPS-based granules containing ED55, whose degradation capacity was further assessed in wastewater with 5 mg/L E2 and compared with that of EPS-granules without bacteria and free ED55 cells. All experiments were conducted in triplicate, and differences among groups were statistically estimated using one-way ANOVA followed by Tukey’s test. EPS-granules with ED55 removed approximately 71% of E2 within 6-hours. After 24-hours, complete removal was achieved and estrone (E1) formation (approximately 60% of the initial E2 concentration) was detected. Free ED55 cells showed faster degradation, achieving complete E2 removal in 1.5-hours. To assess shelf-life of the EPS-granules with ED55, their E2 degradation capacity was tested after three weeks, revealing that they retained their E2-degrading activity and showed removal efficiencies comparable to those observed before. Overall, EPS can act as effective carriers, providing a suitable matrix for preserving the functionality of E2-degrading bacteria over storage.

The work was funded by the project AStUtE (COMPETE2030-FEDER-00780400) financed by the FEDER–Innovation and Digital Transition Programme (COMPETE 2030). CLA acknowledges financial support for her research position through contract ref. 2023.15056.TENURE.048, funded by national funds through FCT – Fundação para a Ciência e a Tecnologia, I.P. The work was supported by national funds through FCT under the projects UID/50016/2025 and LA/P/0076/2020 (https://doi.org/10.54499/LA/P/0076/2020).