Process modelling considerations for the production of lactate from whey using membrane recycle bioreactors operated in continuous and cyclic batch modes

Using a membrane recycle bioreactor (MRB) to produce lactate from whey is potentially more cost effective than a traditional batch fermentation. Membrane recycle bioreactors can be operated in two modes: (1) cyclic batch; (2) continuous. Mathematical modelling of these two modes along with a batch fermentation is used to compare cost and reactor productivity and to examine the effects of selected process and kinetic parameters. Both modes have an optimum operating cell concentration, because there exists an economic trade-off between reactor vessel cost and membrane filtration cost with cell concentration as an optimization variable. The continuous mode is much more sensitive than the cyclic batch to the value of desired residual lactose concentration leaving the reactor, such that, for given kinetic parameters, there exists a value of residual lactose concentration below which the cyclic batch mode becomes more cost effective than the continuous mode. The big disadvantage of cyclic batch is that it is highly sensitive to any cell growth lag time between cycles.