CONTINUOUS, AUTOMATED AND SIMULTANEOUS MEASUREMENT OF OXYGEN-UPTAKE AND CARBON-DIOXIDE EVOLUTION IN BIOLOGICAL-SYSTEMS

Commercial respirometers are capable of continuously and automatically measuring oxygen uptake in bioreactors. A method for continuously and automatically measuring carbon dioxide evolution can be retrofitted t o commercial respirometers. Continuous and automatic measurements of c arbon dioxide evolution are achieved by measuring the change in electr ical conductivity of barium hydroxide solution. Continuous stirring of the barium hydroxide solution was necessary to prevent the carbon dio xide absorption from controlling the oxygen uptake rate. Three separat e experiments (aqueous biodegradation of phenol, soil slurry biotreatm ent of soil contaminated with phenol, and aqueous biodegradation of cr ude oil) were conducted to test the oxygen uptake and carbon dioxide e volution measurement system. The respiratory quotient, defined as the ratio of carbon dioxide evolution to oxygen uptake, is close to one un til a plateau of oxygen uptake is reached, after which it is greater t han one due to degradation of biomass and metabolite products. Unstead y-state simulation of CO2 evolution in batch reactors, based on the ex perimental data, showed that carbon dioxide exists primarily as bicarb onate in the liquid phase. The concentration of carbon dioxide in the gas phase is small mainly due to fast reaction with the stirred barium hydroxide solution.