Effect of Carbon Source on the Migration and Transformation of Sulfate and Rare Earth Elements in Ionic Rare Earth Wastewater by Sulfate-Reduced Anaerobic Digestion (Srad)

Abstract

In sulfate-reduced anaerobic digestion (SRAD), the effect of carbon source on collaborative transformation mechanism of sulfate and rare earth elements (Ree3+) has not received the attention it deserves. Thus, this study explored the transformation of sulfate and Ree3+ under different carbon source conditions. The results showed ethanol underperformed mixed carbon source in removing Ree3+despite its electron competition advantage for following reasons: (1) Under Ree3+ pressure, mixed carbon sources produced more S2-, which converted Ree3+ to sulfides; (2) Microorganisms with mixed carbon sources secreted more tryptophan-like proteins to adsorb Ree3+; (3) CO-SRB (complete oxidizers–sulfate-reducing bacteria) enriched by mixed carbon sources exhibited stronger adaptability to Ree3+ and stronger interactions between species. Besides, the COD/SO42- of 1.5 might be the optimal ratio, which achieved approximately 90% removal of Ree3+ and 69.38 ± 4.63% removal of SO42-. This study provided theoretical guidance for carbon source dosing strategies aimed at simultaneous removal of sulfate and Ree3+ from rare earth wastewater.

Keywords: Ionic rare earth wastewater, Sulfate reduced anaerobic digestion, Carbon source, Carbon and sulfate conversion, Rare earth elements migration