Individual and combined effect of humic acid and fulvic acid on distinct anammox-based systems: Inhibition and resistance.

[Display omitted] • Anammox bacteria was more severely inhibited by FA than HA in both PN/A and PD/A. • PD/A was more robust under HA or FA shocks compared with PN/A. • Combined inhibition of HA and FA was additive on PN/A while antagonistic on PD/A. • HA hindered substrate transport while FA inhibited HZS activity in anammox bacteria. • HA and FA inhibition was alleviated in PD/A by partly participating denitrification. Anammox-based technologies hold great advantages in treating ammonia-rich wastewater where humic substances (HSs), mainly including humic acid (HA) and fulvic acid (FA), are ubiquitous and threaten the anammox activity. Here, the individual and combined effects as well as the mechanism of HA and FA on two typical anammox-based systems, partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A), were investigated. Anammox activity was inhibited by 50 % with 1811.0 mg/L HA and 769.1 mg/L FA in PN/A system, but much higher level of 11706.0 mg/L HA and 5016.0 mg/L FA in PD/A system. The combined inhibition of HA and FA on anammox activity was additive in PN/A but antagonistic in PD/A. Transcription responses of functional genes (hzsA , hzsB , hdh , nirK , and nirS) suggested HA mainly inhibited the transmembrane transport of NH 4 + and NO 2 –, while FA mostly inhibited the activity of intracellular hydrazine synthase (HZS). Interestingly, the strengthened denitrification alleviated the HSs stress on anammox in PD/A. Moreover, the protective microstructure with anammox bacteria encapsulated within abundant Thauera in PD/A granules further prevented PD/A from HSs shock. This study enables a better understanding of the HSs impacts on anammox-based systems, which is critical to integrating anammox technology into actual wastewater treatment. [ABSTRACT FROM AUTHOR]