Substrate Diffusion within Biofilms Significantly Influencing the Electron Competition during Denitrification

Area of Science:

• Environmental Microbiology
• Biochemical Engineering
• Water Treatment Technologies

Background:

• Wastewater denitrification commonly faces operational issues like nitrite accumulation and nitrous oxide emission.
• These intermediates can inhibit biological treatment processes and contribute to greenhouse gas emissions.
• Electron competition between denitrification steps is a known factor, but its role in biofilms is understudied.

Purpose of the Study:

• To assess electron competition dynamics within denitrifying biofilms using a mathematical model.
• To investigate the influence of electron acceptor addition schemes on denitrification intermediates.
• To compare the effects of electron competition on nitrate, nitrite, and nitrous oxide reduction.

Main Methods:

• Development of a mathematical model linking carbon oxidation and nitrogen reduction via electron carriers.
• Simulation of denitrifying biofilms under seven different electron acceptor (nitrate, nitrite, nitrous oxide) addition scenarios.
• Comprehensive analysis of electron competition effects on substrate reduction.

Main Results:

• Electron competition intensified under substrate load limitation (120 to 20 mg COD/L) and increased biofilm thickness (0.1 to 1.6 mm).
• Under these conditions, electrons were preferentially directed to nitrite reductase due to limited electron donor availability.
• Increased effective diffusion coefficients had minimal impact on overall electron competition.

Conclusions:

• Substrate availability and biofilm architecture significantly influence electron competition in wastewater denitrification.
• Prioritization of nitrite reduction under electron-limited conditions can explain intermediate accumulation.
• Mathematical modeling provides valuable insights into complex microbial processes in biofilms.