CONSIDERATIONS IN THE DESIGN OF SIMPLE OVERFLOW DEVICE

The overflow device is an important component in any bioreactor design to ensure that the desired volume of the broth or medium in the working volume remain constant. This is especially required in continuous culture or chemostat and even in activated sludge system. Overflow devices too are required in fed batch culture systems.

Although the primary aim of the overflow device is to maintain the constant volume of the reaction tank, considerations must be taken that the composition of the reaction tank and the wastewater overflow remains homogenous or with the same composition of the media in the reaction tank. In many over flow devices this aspect is not often considered as a very simple attitude is taken just to retain the constant volume in the reaction tank.

In most wastewater bioreactor such as activated sludge and sedimentation tank or even clarifier the over flow device are often too simple in design and function and are located at the interphase of the surface of the water and the air. This would inevitabily resulted in drastic changes in the composition of the wastewater overflows and errors in the sampling procedures.

Having such simple over flow devices in fact help in the enrichment of solids and large particles being retained in the tank.

This characteristic is very crucial if involved in continuous cell cultures as we really need the over flow spent liquour to be truly representative of what really occur in the chemostat.

The overflow device must be located in the truly homogenous zone of the fermentor and where it is continuosly mixed. The design of the overflow device must not in any way changes the physical, chemical and microbiological composition of the sample as it pass through the overflow device

Samplings taken through the overflow device must ensure that dead space samples existing in the overflow device must be completely removed before the real sample taken

The overflow device must be specially designed to ensure aseptic procedures


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