Cell control device for continuous culture reactors.

A device has been developed to increase and control the cell concentration in continuous culture fermentation reactors. This cell control device, used to study mixed culture methane fermentations, was developed because it is necessary to obtain cell concentrations much higher than can be obtained in a single stage reactor by adjustment of residence time or substrate concencentration. Designed around micropore membrane filtration, this unit continuously and completely removes all cells from the effluent and returns them to the reactor. Filtration occurs at the surface of a membrane filter; very little material penetrates into the body of the filter. This filtration surface is quickly clogged by a high cell concentration unless it is continuously cleaned. In this device, the contents of the reactor are continuously pumped tangentially over the filter surface at a velocity sufficient to prevent clogging. Several other arrangements were tried or considered with different directions of flow, moving parts, etc., but this simple arrangement was found sufficient, and it eliminated many mechanical and sealing problems. The cell control device is inserted in the effluent line of the reactor system (Fig. 1), and about 1 atm of vacuum is applied to the filter from the lower side. The circulation pump exerts only a slight, positive pressure on the filter. Cell concentration and substrate concentration are uniform throughout the system because of the high rate of mixing by the circulation pump. Cell concentration is controlled by the amount of sample and wastage removed by means of a side valve. The effluent is collected in an evacuated container and not returned to the reactor system. The cell control device is made from A PVC Process Filter Holder (Millipore Corp., Bedford, Mass.). The modifications are shown in Fig. 2 and 3. The filter holder is made of polyvinyl chloride plastic and is easily modified in an ordinary workshop. The inlet hole in the filter top is enlarged and rounded out with an iron rod heated in a flame. Part of the original hole is