MONITORING BOD IN THE PRESENCE OF HEAVY-METAL IONS USING A POLY(4-VINYLPYRIDINE)-COATED MICROBIAL SENSOR

Interference by heavy metal ions such as Cr3+, Sn2+, Al3+, Co2+, Zn2+, Ni2+, Mn2+, Cu2+ and Ag+, on the response of the Bacillus subtilis/Bacillus licheniformis 7B BOD sensor was effectively eliminated by covering the sensor with a poly(4-vinylpyridine)-coated polycarbonate membrane. The response characteristics of the sensor, with respect to variations in pH, temperature, dissolved alkaline salts, pure organic solutions and wastewater, remained substantially unaffected. The results suggest that a 1 mum thick poly(4-vinylpyridine) film adsorbs heavy metal ions within its structure but at the same time poses no chemical or mass transfer resistance to the diffusion of oxygen or organic solutes from the substrate to the biofilm. Hence, at such thickness, a poly(4-vinylpyridine)-coating eliminates the interference of heavy metal ions with no loss of sensitivity or spectrum of measurable substrates. The mechanism of the elimination is discussed.