Enhancing Mainstream Anaerobic Wastewater Treatment through Electrogenerated Iron Carbonate

Mainstream anaerobic wastewater treatment offers major benefits in energy efficiency and energy recovery but faces challenges with limited nutrient removal and low biogas quality, especially due to sulfides that pose safety and corrosion risks. The in situ production and use of ferrous carbonate (FeCO₃) emerge as a promising strategy to boost anaerobic treatment by removing sulfides and phosphates while upgrading biogas. Although earlier work has shown that FeCO₃ can be generated electrochemically using CO₂ from biogas, its impact on anaerobic treatment has not been well-studied. In this study, FeCO₃ was dosed into an upflow anaerobic sludge blanket (UASB) reactor at 40, 60, and 100 mg of Fe/L, compared to a control reactor. Dissolved sulfide levels were reduced by over 97%, and H₂S was effectively controlled to 100 ppmv at all doses (from 1000 ppmv in the control), with stronger reduction at higher doses. Phosphate removal was also significant, with the highest dose lowering phosphate from 5.0 to 2.5 mg of P/L. X-ray diffraction analysis confirmed that sulfide and phosphate were mainly retained as FeS and Fe₃(PO₄)₂ in the sludge, respectively, offering recovery potential. Additionally, FeCO₃ enhanced organic capture, highlighting the FeCO₃-loop as a sustainable route to improve the anaerobic wastewater treatment.