SIMULATANEOUS BIOKINETIC CHARACTERIZATION OF HETEROTROPHIC AND NITRIFYING POPULATIONS OF ACTIVATED-SLUDGE WITH AN ONLINE RESPIROGRAPHIC BIOSENSOR

The more stringent requirements imposed on wastewater treatment system s result in an increasing demand for on-line monitoring equipment for these processes. The paper presents the modification of a fully operat ional respirographic biosensor to allow simultaneous and on-line bioki netic characterization of both BOD-removal and nitrification capacitie s of activated sludge. For this characterization, advantage is taken o f the calibration measurements that are performed regularly (every 2-3 h) during normal operation of this biosensor. The injection of a well chosen calibration mixture of readily biodegradable BOD and ammonia t o a small activated sludge filled bioreactor results in oxygen uptake rate profiles that are interpreted in the framework of a mathematical model that describes the combined oxygen consumption for BOD removal a nd nitrification. Model identification gives rise to biokinetic parame ters (max. conversion rates and affinity constants) that are indicativ e of the different metabolic capacities of the activated sludge. It is shown that this information can he used to assess the effect of injec ted wastewater samples on the sludge condition, e.g. adaptation or inh ibition, and allows one to follow the change in relative abundance of heterotrophic and nitrifying populations. Special attention is paid to the proper composition of the calibration solution. Especially the ra tio between NOD and BOD is found to be critical. With the aid of simul ation, sub-optimal experimental designs are proposed that allow reliab le equation of the biokinetic parameters. Fully, validation of the pro posed design is given with experimental data.