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.