Simultaneous Fe(III) reduction and ammonia oxidation process in Anammox sludge

Area of Science:

• Environmental microbiology
• Biogeochemical cycles
• Wastewater treatment

Background:

• Reports indicate ferric iron (Fe(III)) reduction to ferrous iron (Fe(II)) in anaerobic environments, coupled with ammonia oxidation.
• Studies on reaction characteristics and mechanisms of this phenomenon are limited.
• Excess ammonia oxidation was observed when studying Fe(III)'s effect on Anammox sludge activity.

Purpose of the Study:

• To investigate the feasibility and characteristics of Anammox coupled to Fe(III) reduction (Feammox).
• To utilize Fe(III) as an electron acceptor instead of nitrite (NO2-) in the Anammox process.

Main Methods:

• Cultivation of Anammox sludge with Fe(III) as the electron acceptor.
• Monitoring ammonia conversion rates and nitrogen species (NO3-, NO2-).
• Quantification of Fe(II) production.
• Sludge analysis using fluorescence in situ hybridization (FISH) and denaturated gradient gel electrophoresis (DGGE).

Main Results:

• Achieved over 80% ammonia conversion after 160 days of cultivation.
• Produced significant amounts of nitrate (NO3-) and a small amount of nitrite (NO2-).
• Reached a total nitrogen removal rate of 71.8% and detected Fe(II) in the sludge.

Conclusions:

• Feammox is a feasible process for nitrogen removal.
• Fe(III) reduction occurs simultaneously with ammonia oxidation to NO2- and NO3- within the Anammox sludge.
• Microbial community analysis indicated retention of Anammox bacteria and enrichment of other microbes during acclimatization.