A pH-control model for heterotrophic and hydrogen-based autotrophic denitrification

Area of Science:

• Environmental Engineering
• Water Chemistry
• Biotechnology

Background:

• Denitrification processes require careful control of water chemistry to maintain optimal conditions.
• Alkalinity, pH, and saturation indices are critical parameters influencing denitrification efficiency and preventing mineral precipitation.
• Existing models may not fully capture the nuances of different denitrification systems, particularly those treating hard groundwater.

Purpose of the Study:

• To develop and validate a predictive model for alkalinity, pH, and Langelier Saturation Index (LSI) in both heterotrophic and autotrophic denitrification systems.
• To provide tools for estimating acid addition (HCl) or pH set points (CO2 sparging) to maintain optimal water chemistry.
• To compare water chemistry dynamics between different stages and denitrification types.

Main Methods:

• Development of a mathematical model integrating chemical and biological parameters of denitrification.
• Experimental validation using two pilot-scale denitrification plants: one heterotrophic (ethanol donor) and one H(2)-based autotrophic.
• Comparative analysis of measured versus predicted alkalinity, pH, and LSI in both systems and across different stages.

Main Results:

• The model accurately predicted alkalinity, pH, and LSI in both tested denitrification systems.
• Significant differences in alkalinity and pH were observed between Stage-1 and Stage-2 of the denitrification process.
• Distinct pH and LSI profiles were found between the two systems, despite similar alkalinity increases, highlighting system-specific chemical behaviors.

Conclusions:

• The developed model offers a reliable method for predicting and managing water chemistry in diverse denitrification systems.
• The study elucidates key differences in water chemistry between heterotrophic and autotrophic denitrification, informing process optimization.
• Recommendations are provided for acid addition strategies, favoring CO2 for autotrophic and HCl for heterotrophic systems to prevent scaling and maintain optimal pH.