Insight into the role of anthraquinone on the denitrifying phosphorus removal system under perfluorooctanoic acid stress

Anthraquinone (AQ) is known to accelerate biochemical reactions. This study investigated the mechanisms by which AQ supplementation enhanced the performance of a denitrifying phosphorus removal (DPR) system under perfluorooctanoic acid (PFOA) inhibition, compared to natural recovery conditions. Results showed that supplementation with 100 μmol/L AQ obviously improved the removal efficiencies of PO₄^3--P, total nitrogen, and chemical oxygen demand (COD), reaching 2.26-, 1.16-, and 1.09-fold higher, respectively, than those in the control group. Concurrently, AQ increased the activities of polyphosphate kinase (PPK), polyphosphate exopolymerase (PPX), and nitrate reductase (NAR) by 2.16-, 1.45-, and 1.19-fold, respectively, relative to the PFOA stress period. Furthermore, the addition of AQ stimulated the growth of AQ-degrading denitrifying polyphosphate-accumulating organisms (DPAOs), which catalyzed the redox conversion between AQ and hydroquinone. This redox cycling generated electrons that facilitated more efficient electron exchange among microbial populations. The increased relative abundance of DPAOs correlated with elevated abundances of key genes involved in nitrogen metabolism, phosphorus cycling, and internal carbon storage pathways, thereby contributing to an overall improvement in metabolic performance under PFOA stress.