Decoupling Dissolution and Biological Kinetics in Polycaprolactone-Based Denitrification: Direct Determination of...

Area of Science:

• Environmental Microbiology
• Biotechnology
• Water Treatment Engineering

Background:

• Solid-phase denitrification using biodegradable polymers is a sustainable alternative to soluble carbon dosing.
• Mass-transfer and dissolution limitations in polycaprolactone (PCL)-based systems obscure true biological kinetics.
• Accurate kinetic and stoichiometric parameters are crucial for optimizing nitrogen removal processes.

Purpose of the Study:

• To experimentally determine biomass yield (Y) and maximum specific growth rate (μmax) for PCL-based denitrification.
• To decouple the PCL dissolution step from microbial growth for direct kinetic measurements.
• To compare the biological performance of PCL with methanol as a soluble carbon source.

Main Methods:

• PCL was presolubilized to decouple dissolution from microbial growth.
• Anoxic batch experiments were conducted to determine biomass yield and growth rates.
• High-frequency batch testing and SUMO process modeling were used to analyze nitrate depletion.

Main Results:

• Biomass yields for methanol and presolubilized PCL were comparable (0.35 ± 0.08 and 0.38 ± 0.08 g COD/g COD, respectively).
• Maximum specific growth rates (μmax) were higher for PCL (2.1 day⁻¹) than for methanol (1.3 day⁻¹) under decoupled conditions.
• Slower carbon release from PCL, not biological limitations, explained lower net biomass accumulation in long-term tests.

Conclusions:

• This study provides the first direct, hydrolysis-independent kinetic parameters for PCL-based denitrification.
• Apparent kinetic limitations in solid PCL systems are primarily due to mass-transfer, not biological capacity.
• Design-ready kinetic parameters for biodegradable polymers facilitate their integration into predictive models for sustainable nitrogen removal.