The Simultaneous Efficient Recovery of Ammonia Nitrogen and Phosphate Resources in the Form of Struvite: Optimization and Potential Applications for the Electrochemical Reduction of NO3. Molecules 2024;29:2185. [PMID: 38792046 PMCID: PMC11123745 DOI: 10.3390/molecules29102185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In response to the need for improvement in the utilization of ammonium-rich solutions after the electrochemical reduction of nitrate (NO3--RR), this study combined phosphorus-containing wastewater and adopted the electrochemical precipitation method for the preparation of struvite (MAP) to simultaneously recover nitrogen and phosphorus resources. At a current density of 5 mA·cm-2 and an initial solution pH of 7.0, the recovery efficiencies for nitrogen and phosphorus can reach 47.15% and 88.66%, respectively. Under various experimental conditions, the generated struvite (MgNH4PO4·6H2O) exhibits a typical long prismatic structure. In solutions containing nitrate and nitrite, the coexisting ions have no significant effect on the final product, struvite. Finally, the characterization of the precipitate product by X-ray diffraction (XRD) revealed that its main component is struvite, with a high purity reaching 93.24%. Overall, this system can effectively recover ammonium nitrogen from the NO3--RR solution system after nitrate reduction, with certain application prospects for the recovery of ammonium nitrogen and phosphate.

Quantitative, morphological, and structural analysis of Ni incorporated with struvite during precipitation

Struvite precipitation is a promising strategy for the simultaneous recovery of nitrogen and phosphorus from waste streams. However, waste streams typically contain high amounts of metal contaminants, including Ni, which can be easily sequestered by struvite, but the behavior of Ni during struvite precipitation remains unclear. Thus, this study investigates the influence of Ni concentrations on struvite precipitation. The quantitative X-ray diffraction (QXRD) results revealed that the purity of struvite decreased from 96.6 to 41.1% with the Ni concentrations increased from 0.1-100 mg·L^-1. At lower Ni concentrations of 0.1-1 mg·L^-1, scanning electron microscopy (SEM) showed a roughened surface of struvite crystal, and this was combined with X-ray absorption near edge structure (XANES) data that indicated a stack of Ni-OH and Ni-PO₄ on struvite surface. At Ni concentrations of 10-25 mg·L^-1, Ni primarily crystalized as Ni-struvite (NiNH₄PO₄·6H₂O), as detected by QXRD. At higher Ni concentrations of 25-100 mg·L^-1, the co-precipitation of amorphous Ni phosphate(s) (e.g., Ni₃(PO₄)₂) and Ni hydroxide (e.g., Ni(OH)₂) was identified by XANES. Specifically, the X-ray photoelectron spectroscopy (XPS) analysis detected the formation of amorphous Mg hydroxide(s) and phosphate(s) at Ni of 25-100 mg·L^-1. The overall results revealed that Ni formed Ni-OH and Ni-PO₄ on struvite surface at 0.1-1 mg·L^-1, whereas Ni precipitated as separated phases (e.g. Ni-struvite, Ni hydroxide and phosphate) at 10-100 mg·L^-1. The existence of Ni disturbed the crystal growth of struvite and promoted the formation of Ni-struvite, amorphous products during struvite formation.

Unified prebiotically plausible synthesis of pyrimidine and purine RNA ribonucleotides

Theories about the origin of life require chemical pathways that allow formation of life's key building blocks under prebiotically plausible conditions. Complex molecules like RNA must have originated from small molecules whose reactivity was guided by physico-chemical processes. RNA is constructed from purine and pyrimidine nucleosides, both of which are required for accurate information transfer, and thus Darwinian evolution. Separate pathways to purines and pyrimidines have been reported, but their concurrent syntheses remain a challenge. We report the synthesis of the pyrimidine nucleosides from small molecules and ribose, driven solely by wet-dry cycles. In the presence of phosphate-containing minerals, 5'-mono- and diphosphates also form selectively in one-pot reactions. The pathway is compatible with purine synthesis, allowing the concurrent formation of all Watson-Crick bases.