Direct parameter extraction from respirograms for wastewater and biomass characterization

A method is proposed and described that calculates model parameters and components through a series of numerical transformations on respirometric data. The method is direct because it does not use a model optimisation technique. This direct respirogram evaluation (DRE) method separates the respirogram into individual components, and calculates maximum respiration rate, saturation coefficient and yield factor for the components. An advantage of the DRE method is the simplicity; there are no complications involving modelling, optimisation, and model identifiability. The calculations are model independent, even though the principle implies the Monod saturation term. The most important limitation is that only certain types of respirograms can be identified, that is: individual components must be dominant at a critical stage of their oxidation. The DRE method is tested on simulated respirograms and a number of real respirograms of various characteristics, and the results from the latter are compared to those from a parameter optimisation method. It is concluded that the two methods are not always in agreement, especially when a component is present in a minor fraction.