EFFECT OF HEAVY-METAL IONS ON THE EFFICACY OF A MIXED BACILLI BOD SENSOR

Heavy metal ions such as cadmium, mercuric, lead, chromic, stannous, ferrous, ferric and aluminium at a concentration of 4 mM have negligible or no effect on the BOD sensing of a mixed Bacillus subtilis and Bacillus licheniformis 7B microbial BOD sensor. In the presence of cobalt, zinc and nickel ions, the BOD measured by the sensor was higher than the true value of the test solution. This was attributed to the increase in the microbial activity by the metal ions present. Cupric and in particular silver ions significantly suppressed the microbial assimilation of the substrate resulting in a lower measured BOD value of the substrate. The interference of silver and cupric ions on the BOD measurement were successfully eliminated by chelating these ions with EDTA or by phenotypic modification of the microbial system by pre-conditioning the sensor in a BOD solution containing the interfering ions.