Development of an automated dynamic method for <i> k _L a </i> determination and its application to pollutant-influenced oxygen transfer

<b>ABSTRACT</b>The volumetric oxygen mass transfer coefficient (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:mi>a</mml:mi></mml:math>) is a critical parameter in the design, scale-up, and operation of bioreactors. In this study, a fully automated dynamic method was developed for determining <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:mi>a</mml:mi></mml:math>, eliminating manual intervention and ensuring reproducible and reliable estimates. The approach includes a probe response-time correction and was validated under different operational conditions in an aerated stirred system. The influence of two representative pollutants was evaluated: phenol and benzalkonium chloride (BAC). While phenol produced a small enhancement (≈18%) of the overall <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:mi>a</mml:mi></mml:math>, BAC caused a reduction in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:mi>a</mml:mi></mml:math>, mainly due to its pronounced effect on the surface mass transfer coefficient (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi><mml:mi>L</mml:mi></mml:msub><mml:msub><mml:mi>a</mml:mi><mml:mi>S</mml:mi></mml:msub></mml:math>). To the best of our knowledge, this work provides the first experimental evidence of BAC effects on oxygen transfer in bioreactors. These results expand the current understanding of how pollutants can simultaneously act as metabolic inhibitors and as modifiers of gas-liquid mass transfer, with significant implications for optimising aeration strategies in biological wastewater treatment.