Recovery of NH4+‒N and PO43-‒P is Promoted by competitive interactions between M. aeruginosa and MgCO3

ABSTRACT : Here we report that the presence of MgCO 3 stimulates the extracellular polymeric substance (EPS) secretion of Microcystis Aeruginosa ( M . Aeruginosa ). This stimulation led to a significant reduction in the total concentration of NH 4 + ‒N by more than 86％, and effective recovery of PO 4 3- ‒P within three days from concentrated wastewater (WW), although the secreted EPS inhibited the conversion of MgCO 3 to specific crystal forms (MgNH 4 PO 4 .6H 2 O or MgHPO 4 .7H 2 O). Moreover, with an increase in PO 4 3- concentration in WW, these crystals appeared, thus the removal of NH 4 + ‒N and PO 4 3- ‒P nutrients can be attributed to the combined effect of M. Aeruginosa and MgCO 3 . We used Surface-Enhanced Raman Spectroscopy (SERS) combined with X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (FESEM-EDS), and X-ray Photoelectron Spectroscopy (XPS) to investigate the mechanism for competitive interactions between M. Aeruginosa and MgCO 3 in removing NH 4 + ‒N and PO 4 3- ‒P. We identified that the bound EPS accumulated amorphous Mg−P−O dense particles on M. Aeruginosa , while soluble EPS, containing ‒COOH groups of humic-like substances decreased the pH of the solution and coordinated with Mg 2+ ions. Therefore, both secreted bound and soluble EPS play a vital role in hindering the transformation of Mg 2+ ions or MgCO 3 to MgNH 4 PO 4 .6H 2 O or MgHPO 4 .7H 2 O crystals within WW, and they enhanced M. Aeruginosa 's ability in absorbing nutrients of NH 4 + ‒N and PO 4 3- ‒P. This mechanism plays a crucial role in the efficient recovery of NH 4 + ‒N and PO 4 3- ‒P from concentrated wastewater sources such as aerobically or anaerobically digested effluent from various sources like agriculture, livestock, and domestic wastewaters. • Coupling of M. Aeruginosa with MgCO 3 efficiently removes concentrated NH 4 + ‒N and PO 4 3- ‒P. • Addition of MgCO 3 prompts M. Aeruginosa to secrete EPS, and therefore significantly improves removal efficiency. However, this blocks the conversion of MgCO 3 to MgNH 4 PO 4 .6H 2 O. • Competition for NH 4 + ‒N and PO 4 3- ‒P between M. Aeruginosa and MgCO 3 is highly relevant for EPS secreted by M. Aeruginosa. Sustainable management of wastewater in diverse settings needs to develop effective strategies for nutrient removal and wastewater treatment. We report a mechanism for the competitive interactions between M. Aeruginosa and MgCO 3. This mechanism plays a crucial role in the efficient recovery of NH 4 + ‒N and PO 4 3- ‒P from concentrated wastewater sources such as aerobically or anaerobically digested effluent from various sources like agriculture, livestock, and domestic wastewaters.