ON LINE GROWTH MEASUREMENTS IN BIOREACTORS BY TITRATING METABOLIC PROTON-EXCHANGE

Recording the amount of titrant required to maintain constant pH in a bioreactor where cell metabolism causes acidity changes allows on-line determinations of growth kinetics in computer-controlled batch cultur es. A system for making such measurements is described and its perform ance is investigated. Transient bicarbonate accumulation occurs if the culture produces CO2 at high pH values and low gas transfer rates. We have developed a mathematical model for the titrant requirement as a function of the cell growth rate, the gas transfer properties of the b ioreactor and the culture pH. According to this model, bicarbonate acc umulation affects the stoichiometry between titrant and biomass but do es not prevent determination of growth rate constants. These predictio ns are confirmed using model experiments and measurements during batch growth of microbial cultures.