Insights into the response of biological nitrogen removal process to organophosphate esters and the adaptive mechanisms of microbial community

The increasing organophosphate esters (OPEs) in wastewater have aroused great concerns, but their impacts on biological nitrogen removal process remained unclear. The effects of two ubiquitous OPEs, tris(2-chloroethyl) phosphate (TCEP) and tris(n-butyl) phosphate (TnBP), on biological nitrogen removal performance and microbial community were explored in activated sludge system. The results indicated that nitrogen removal efficiency remained stable (71.29%$-$75.65%) with OPEs increased. Nitrite oxidation and denitrification processes were inhibited by high TnBP and TCEP concentrations, respectively. OPE-tolerant denitrifying bacteria (e.g., Azonexus, Methyloversatilis) were enriched under OPEs exposure. The oriented community succession resulted in more important deterministic process in community assembly and more interactions between nitrogen removal bacteria. Molecular ecological networks analysis indicated that more cooperation of keystone and functional taxa enhanced community stability under OPEs stress. The nitrogen metabolic functions were stimulated with increasing OPEs concentration, and the function of xenobiotics degradation was upregulated as the OPEs degradation bacteria enriched, which would alleviate the negative impacts of OPEs on the nitrogen removal process. Furthermore, carbon metabolic and electron transfer functions were altered to alleviate OPEs stress and facilitate denitrification. This study would provide new ecological insights into the adaptive evolution of microbial community to emerging contaminants in biological nitrogen removal systems.