Respirometry measures the biological oxygen consumption rate under well-defined conditions and is commonly used to determine kinetic and stoichiometric parameters of microbial cultures. Compared to techniques based on substrate concentration, respirometry allows for parameter estimation with relatively small experimental effort while obtaining high-quality data. Within many respirometry techniques, pulse respirometry is one of the most commonly used and consists of measuring DO after injecting into the system a pulse of defined substrate concentration. The exogenous oxygen uptake rate curves reflect the aerobic biodegradation process, and allow estimation of kinetic and stoichiometric parameters by direct model fitting to a respirometric curve.
Relatively recently, microscale bioreactors have become standard equipment in bioprocess laboratories. Most microreactor systems include DO sensors, making them a convenient tool for simultaneous respirometry measurements in 6 to 96 batch microbial cultures. However, despite its potential, pulse respirometry has never been reported in microreactors.
In this research, pulse respirometry was assessed in a Pall Micro-24 system, one of the most widespread equipment used in bioprocess laboratories. Four different cultures were used: two axenic cultures of Pseudomonas putida F1 and Escherichia coli sp. and two mixed cultures of synthetic wastewater sludge and nitrifying sludge. In these four cultures, the substrate affinity constant (KS), the maximum specific growth rate (μmax) and the growth yield (YX/S), within others, were successfully determined. It is concluded that pulse respirometry in microreactors is a powerful tool for the characterization of microbial processes with lower standard error and experimental time than in standard bioreactors or respirometers.