2.3 In situ product removal (ISPR) processes by microfiltration

A polypropylene membrane, Accurel PP, consisting of a long capillary (5–10 m) with an inner diameter of 0.2 mm and a cutoff of 0.22 µm was used for the construction of the microfiltration module. Briefly, 15 capillaries 15- cm long were obtained from the original membrane and assembled with a silicon adhesive; one side was closed and the other was sealed to a connector. The module was connected to a peristaltic pump (model 313 U; Watson Marlow, Falmouth, United Kingdom) equipped with a silicon tube, with an inner diameter ϕ = 2 mm, which provided the driving force for transmembrane flux. Considering the geometry of the module, the total filtering area measured 600 cm². Before using the module, the membranes were treated with a 70% ethanol solution for 1 h to improve hydrophilicity. The microfiltration module was placed inside the fermentation vessel and fixed vertically to a baffle to have a high turbulence near the filtering surface thereby minimizing fouling. Finally, the membrane modules were in situ sterilized together with the medium at 90°C for 45 min to avoid deconstructing the adhesive silicone.