Comparison of methods for the determination of K_La_O2 for respirometric measurements

The mass transfer coefficient for oxygen in water (K_La_O2) is an important parameter for respirometric studies. But determination of K_La_O2 in process conditions is not straightforward. In this paper, two distinct procedures for determining K_La_O2 in process conditions are outlined and tested. The off-gas method relies on a gas mass balance over a bioreactor while the non-steady state methods rely on analysing DO recovery after perturbation. Various means for inducing perturbation are tested and compared. K_La_O2 values for a bioreactor are determined by the listed methods. It was found that the off-gas method resulted in the highest K_La_O2 for the given reactor, while the non-steady state method, whereby perturbation is caused by exogenous activity on acetate, resulted in the lowest K_La_O2. It is shown that the gas mass balancing technique is robust to unexpected exogenous activity (caused by for example, the oxidation of storage polymers formed or nitrite accumulated), while the non-steady state methods that involve inducing perturbations by exogenous activity appear susceptible to such continued exogenous activity in the DO recovery period.