Enhancement of static magnetic field on nitrogen removal at different ammonium concentrations in a sequencing batch reactor: Performance and biological mechanism

This study aimed to investigate the effects and biological mechanism of external static magnetic fields (SMFs) on enhancing nitrogen removal at different influent ammonium nitrogen (NH4+) concentrations. Four sequential batch reactors (SBRs) with SMFs of 0, 15, 30, and 50 mT were operated continuously for 196 days, during which the influent NH4+-N concentration increased stepwise as 50, 100, 350, and 600 mg L-1. The results showed that 50 mT had optimum effects on enhancing nitrogen removal, especially at high NH4+-N concentrations (350 and 600 mg L-1). The biological mechanism by which SMF influences nitrogen removal varies depending on the NH4+ concentration. At low NH4+-N concentrations (50 and 100 mg L-1), a field of 50 mT increased key enzyme activities and corresponding functional gene abundances. Additionally, it further improved functional bacterial abundances, which involved nitrifying and denitrifying bacteria at high NH4+ concentrations. These findings could provide guidance for the selection of optimum SMF intensity at different influent NH4+ concentrations. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study found that a static magnetic field of 50 mT had the best effect on enhancing nitrogen removal, especially at high NH4+ concentrations. The biological mechanism by which SMF influences nitrogen removal varies depending on the NH4+ concentration, increasing key enzyme activities and functional gene abundances, as well as improving functional bacterial abundances.