Comparison of methods for the determination of K(L)aO2 for respirometric measurements

The mass transfer coefficient for oxygen in water (K(L)aO2) is an important parameter for respirometric studies. But determination of K(L)aO2 in process conditions is not straightforward, In this paper, two distinct procedures for determining K(L)aO2 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(L)aO2 values for a bioreactor are determined by the listed methods. It was found that the off-gas method resulted in the highest K(L)aO2 for the given reactor, while the non-steady state method, whereby perturbation is caused by exogenous activity on acetate, resulted in the lowest K(L)aO2. 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.