Bacterial Turbidity Optical Measurement Research

Microbial fermentation is a complicated process that is influenced by many variables. Living cell concentration is one of the most important variables among them. The on-line information of cell concentration is useful for calculation of some of the physiological state variables, like the specific growth rate et al., and for optimal control of fermentation process. So it is necessary to develop an on-line monitoring system for measuring cell concentration in real-time during fermentation process.In this research, the cell concentration was on-line measured by the turbidity of the fermentation broth, as there was a linear relationship between the cell concentration and the turbidity of the fermentation broth.The wavelength and photosensitive sensor affect the measurement accuracy greatly. Near infrared ray laser with the wavelength of 632 nm was used instead of the complicated optic system in traditional instruments, which made the apparatus simple and small and convenient for on-line turbidity measurement.Several kinds of photosensitive sensors, integrated operational amplifiers and magnified circuit of photosensitive sensors were integrated and tested, and the merits and demerits of them were compared. Finally, the electric eye was chosen as the photosensitive sensor and the corresponding amplifier circuit was designed.The apparatus developed includes several parts. The first part, the photosensitive sensor, transforms the optical signal of turbidity to electrical signal. The second part, the operation amplifiers, amplifies the original electrical signal. The third part, the A/D converter and the signal collection card together with the virtual instruments software written in LabVIEW, transfer the amplified signal to the computer.The software developed using Lab VIEW has the functions of signal input, data saving, dynamic display, and dynamic figuring. Lab VIEW is the graphical language, which has many merits, such as good user interface, very easy to operate and maintain, and can save much time and money of the developer.Through real fermentation test, this system was confirmed to be stable, have good performance and easy to use. The on-line monitoring result is satisfactory compare with the off-line measured cell growth curve. The apparatus developed in this research will be of great useful in automation of fermentation technology.Computer control of fermentation process has significance in reducing operating costs, improving efficiency and product quality. Along with the fast development of electronics and computer technology in China, fermentation automation will develop fast soon. We can see that it has great opportunities and economical benefits to revolutionize the traditional fermentation technology using automation technology.