Estimating biomass yield coefficients for autotrophic ammonia and nitrite oxidation from batch respirograms

Kinetic characterization of biological processes via batch respirometry requires an accurate estimate of the biomass yield coefficient because it provides the stoichiometric link between biomass synthesis, substrate consumption and oxygen uptake. Expressions for biomass yield coefficients describing autotrophic ammonia and nitrite oxidation were derived from a mechanistically based electron balanced equation. We demonstrate that applying the conventional expression used to calculate the heterotrophic biomass yield results in erroneous estimates for the autotrophic biomass yield. Yield coefficients for autotrophic NH4+–N to NO2−–N oxidation and NH4+–N to NO3−–N oxidation were overestimated by 27 to 36%. Due to correlation between the maximum specific growth rate and the biomass yield, the error in yield values propagated in 30 to 40% overestimates of the maximum specific growth rate coefficient for NH4+–N oxidation determined from batch respirograms. Therefore, it is essential to employ the correct expression to estimate the autotrophic biomass yield coefficient from batch respirograms due its inadvertent impact on subsequent parameter estimation.