Figure 1. Sketch of the fermentor is shown with all the connection for monitoring and control of the continuous lactic acid fermentation process with continuous cell recycling.

F₁: feed rate (the dilution rate was maintained by maintaining the feed rate);
F₂: rate at which broth was taken out of the fermentor;
F₃: rate of purging (the sample from the purge were regularly analyzed for biomass and metabolites concentrations inside the fermentor);
F₄: rate at which permeate was taken out from the filtration unit;
F₅: rate at which biomass was recycled back to the fermentor.