Homklin S.Satiraphan M.Thayanukul P.Charanaipayuk N.Yagi T.Limpiyakorn T.Mahidol University2025-08-172025-08-172025-10-01Process Safety and Environmental Protection Vol.202 (2025)09575820https://repository.li.mahidol.ac.th/handle/20.500.14594/111697The synthetic androgen 17α-methyltestosterone (MT) has been widely employed to produce all-male populations in Nile tilapia farming. Improper treatment of aquaculture effluent may lead to the release of unconsumed or unmetabolized MT into surrounding water bodies, posing potential risks to aquatic ecosystems. This study evaluated the efficacy of biofilter reactors in removing MT and its associated androgenic activity from discharge. To promote biofilm formation, laboratory-scale biofilter reactors were supplied with synthetic freshwater containing MT-free pulverized fish feed. Compared to control reactors without biofilm, the biofilm reactors exhibited significantly greater MT removal efficiency (47.0 ± 0.8 % vs. 8.8 ± 2.7 %), highlighting the crucial role of biofilms in MT removal. When synthetic freshwater containing an environmentally relevant concentration of MT (40 μg/L) was introduced, the biofilter reactors achieved a removal efficiency of 43.5 ± 1.6 %. Supplementation of the influent with fish feed, carbon-free minimal medium (CFMM), or CFMM plus glucose further enhanced MT removal to 98.9 ± 0.5 %, 84.5 ± 3.3 %, and 89.5 ± 4.6 %, respectively. Corresponding reductions in androgenic activity, as assessed via a yeast reporter gene assay, were also substantial: 83.7 ± 6.7 % and 84.1 ± 5.8 % for the influents supplemented with fish feed and CFMM plus glucose, respectively. These findings suggest that nutrient supplementation facilitates microbial degradation of MT. 16S rRNA gene amplicon sequencing revealed a diverse microbial community within the biofilm, including genera such as Achromobacter, Cupriavidus, Gordonia, Rhodococcus, Sphingomonas, and Stenotrophomonas-previously been implicated in the degradation of MT, androgens, estrogens, or sterols. Since no single genus was consistently detected across all reactors, MT degradation appears to result from the collective activity of a diverse microbial consortium rather than specific MT-degrading taxa alone. Notably, acclimation with MT to induce degradation activity was not required. The indigenous microorganisms present in the initial fish feed-fed biofilm were already capable of MT removal, and their activity was further enhanced by nutrient supplementation.Chemical EngineeringEnvironmental ScienceEngineeringArticleSCOPUS10.1016/j.psep.2025.1076822-s2.0-105012988171