Synergistic transformation of alkylbisphenols (BPA, BPE, and BPF) mediated by ammonia-oxidizing bacteria and heterotrophic bacteria in nitrifying activated sludge

Transformation of bisphenol compounds during nitrogen removal processes in wastewater treatment plants, along with the key microbial taxa associated with this transformation, remains poorly understood. In this study, we examined the transformation of a series of alkylbisphenols (ABPs; bisphenol A, bisphenol E, and bisphenol F) and sulfonylbisphenol (bisphenol S) in an enriched nitrifying activated sludge (NAS). While bisphenol S was persistent in the NAS, the ABPs were effectively transformed; however, 14 C-isotope tracing revealed that the majority of BPA (presumably also other ABPs) was retained in the NAS as transformable intermediates and potentially toxic nitroaromatic compounds, with minor mineralization (< 1 %). In total, nine transformation products were identified, including nitrated aromatic compounds and single-ring phenolic compounds. Ammonia‑oxidizing bacteria (AOB), primarily Nitrosomonas , drove abiotic ABP transformation to persistent nitroaromatic products. Heterotrophic bacteria, such as Sphingomonas , Methyloterena , and Comamonas , initiated ABP transformation via type II ipso- hydroxylation and oxidative cleavage, and also mineralized the intermediates formed through the AOB-mediated dealkylative nitration. By integrating batch experiments, HPLC–QTOF-MS/MS, 14 C-tracing, and 16S rRNA gene sequencing, we provide a comprehensive understanding of these complementary transformation pathways and the key microbial taxa involved. Our findings highlight the significant role of AOB-mediated abiotic reactions in ABP transformation, and alarmingly revealed that the traditional nitrogen removal processes using NAS may produce toxic persistent nitroaromatic compounds, thereby leading to unexpected environmental risks.