PROBLEMS OF SAMPLING

Everybody knows why we carry out sampling. We carry out samplings or obtaining samples so that we can have information or data of the system being sampled. The samples obtained are analyzed and the data obtained are used by us so that we can “extrapolate” or “guess” about the composition status of the system being studied.

In certain systems being studied such as fermenters, they are even equipped with specific purpose built sampling ports where samples can be obtained for analyses.

The sampling ports are often designed more for the ease of sampling or aseptic integrity rather than for the purpose of a truly representative sample!

It is very important in any sampling that the samples obtained are truly representative of the system so as to truly reflect the composition of the system. A non truly representative sample will have the tendency to give inaccurate reading. As they often say, the results obtained are as good as the sample itself. Analyses of the sample is only valid for the sample itself and will not truly reflect the status of the system.

Many users of fermentors when using the samplers do not often reflect the weak links in the process of sampling and to put complete trust that the samples they obtained are very accurate and reflecting the real composition of the fermentation process.

It is important that since a lot depend on the samples and sampling process itself that a proper sampling plan be properly prepared to take into account the weaknesses of such samplings.

They need to carry out preliminary studies and validate their sampling procedures so that their data is acceptable and trust worthy. One of the key areas they must look into is the homogeneity of the fermentor content and statistical validity of their sampling


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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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