In a continuous reactor, the medium contains 40 g.l-1 of maltose and the medium flow rate is 10 litres per hour and the effluent contains 20 g.l-l of lactate. What is the productivity of lactate production from this reactor?

The residence time can be calculated using the inverse of the dilution rate. In the case of a continuous reactor with a dilution rate (often denoted by ‘D’) of 0.5 h^-1, the residence time (‘τ’) would be the inverse of this, so τ = 1/D. Hence, given D=0.5 h^-1, τ = 1/0.5 = 2 hours.