Nitrate reduction by denitrifying anaerobic methane oxidizing microorganisms can reach a practically useful rate

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Technologies
• Biogeochemical Cycles

Background:

• Methane from biogas can serve as an electron donor for complete nitrogen removal via denitrifying anaerobic methane oxidizing (DAMO) microorganisms.
• The practical application of DAMO processes is hindered by the slow growth and low activity of these microorganisms.
• Integrating DAMO with anaerobic ammonium oxidation (anammox) offers a potential pathway for enhanced nitrogen removal.

Purpose of the Study:

• To evaluate the nitrate reduction capacity of a lab-scale membrane biofilm reactor (MBfR) co-culturing DAMO and anammox microorganisms.
• To determine if the achieved nitrate removal rate is sufficient for practical wastewater treatment applications.
• To assess the feasibility of using DAMO to mitigate nitrate accumulation in anammox reactors.

Main Methods:

• Operation of a lab-scale membrane biofilm reactor (MBfR) with a mixed microbial community of DAMO and anammox bacteria.
• Progressive increase of nitrate and ammonium loading rates to assess reactor performance under varying conditions.
• Mass balance analysis to quantify the contributions of anammox and DAMO bacteria to nitrogen transformation.

Main Results:

• A record nitrate removal rate of 684 ± 10 mg-N L(-1) d(-1) was achieved after 453 days of operation.
• The achieved rate significantly exceeds the predicted requirements for nitrate removal in both sidestream and mainstream anammox reactors.
• Nitrite was co-metabolized by anammox bacteria (354 ± 3 mg-N L(-1) d(-1)) and DAMO bacteria (330 ± 9 mg-N L(-1) d(-1)), supporting ammonium removal (268 ± 2 mg-N L(-1) d(-1)).

Conclusions:

• The nitrate reduction rate achieved by the DAMO process in this study is sufficiently high for practical wastewater treatment.
• This demonstrates the potential of integrating DAMO bacteria with anammox processes for complete nitrogen removal from wastewater.
• The findings overcome previous doubts regarding the practical utility of DAMO microorganisms in engineered systems.