Effects of pre-conditioning and microbial composition on the sensing efficacy of a BOD biosensor.

Sensitivity and the linear range of BOD measurement of a microbial BOD sensor using a mixed cell population of Bacillus subtilis and Bacillus licheniformis 7B depend significantly on the proportion of the two microorganisms and on the cell population immobilized on the biofilm. Optimum characteristics were obtained with equal proportion of the two microorganisms and an immobilized cell population of not less than 10(8) in the biofilm. Pre-conditioning of newly installed biofilm was best carried out in high BOD solutions and the time required to fully activate the microbial system decreased with increasing cell population. Fully activated biofilm remained stable and gave reproducible results for over 200 measurements covering a time period of more than 2 months. The technique of cell immobilization used in the present study provided a close control of the population and composition of the two microorganisms in the biofilm. Consistent and reproducible quality biofilms can therefore be produced for the preparation of the microbial BOD sensor.