Denitrification Biokinetics: Towards Optimization for Industrial Applications

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Biotechnology

Background:

• Denitrification is crucial for industrial processes like souring control and microbially enhanced oil recovery (MEOR).
• The bacterium *Thauera* is dominant in these applications, but its denitrification kinetics under varying conditions are not well understood.
• Optimizing denitrification requires knowledge of nitrate (NO₃^-), nitrite (NO₂^-), and pH impacts.

Purpose of the Study:

• To investigate the effects of nitrate and nitrite concentrations and pH on denitrification kinetics by *Thauera* strains.
• To understand how these parameters influence the partial or complete reduction of nitrate to nitrogen gas (N₂).
• To provide insights for optimizing *Thauera*-mediated denitrification in industrial applications.

Main Methods:

• Studied denitrification kinetics of three *Thauera* strains (K172, NS1, TK001) using acetate as an electron donor.
• Varied initial nitrate concentrations and monitored nitrate, nitrite, and nitrous oxide (N₂O) levels.
• Assessed the impact of pH on denitrification rates and gene expression (*nirS*, *nosZ*).

Main Results:

• Complete nitrate reduction occurred at low nitrate concentrations (∼1 mmol L^-1) and pH 7.5.
• Denitrification rates varied among strains, with NS1 being significantly slower.
• Elevated nitrate concentrations, nitrite accumulation, and pH > 9 inhibited denitrification rates and N₂ production.
• High pH and nitrite accumulation affected denitrification gene expression and increased stress on certain strains.

Conclusions:

• Increased pH can be used to achieve partial denitrification (promoting NO₂^- and N₂O production for souring control).
• pH buffering is recommended for complete denitrification to N₂ (for gas-mediated MEOR).
• Understanding these kinetics is vital for tailoring microbial processes in industrial settings.