Influence of organic acids on phosphorus recovery via vivianite crystallization: New insights based on spectroscopic analysis and DFT calculations

Recovering phosphorus (P) as vivianite from P-rich wastewater has become a focal point of attention due to increasing P demand and eutrophication risks. The anaerobic fermentation supernatant, as a promising target for P recovery, commonly contains organic acids such as acetic acid and propionic acid, which may influence the formation of vivianite crystals. This study investigated the influence of organic acids on the phosphorus recovery from synthetic anaerobic fermentation supernatant through vivianite crystallization. The interaction mechanism was explored with various spectroscopic analyses and density functional theory (DFT) calculations from molecular and atomic levels. The results indicated that organic acids exerted negligible inhibition on P recovery at low concentrations, but caused significant suppression at high concentrations (>700 mg/L). Both acetic and propionic acids led to approximately 8 % inhibition at 1000 mg/L. The organic acids had minimal impact on the overall crystal structure and size distribution of vivianite, but they noticeably altered the surface morphology. Surface complexation, coordination reactions, and chemical bonding between organic acids and vivianite surfaces impeded crystal growth and induced alterations in electronic states. Notably, DFT calculations indicated that propionic acid exhibited a stronger adsorption affinity than acetic acid, thereby affecting crystal growth and electronic states. The experimental results shed light on the relationship between organic acid concentration and the formation of vivianite crystals, providing valuable insights for optimizing P recovery strategies.