BOD measurement in the presence of heavy metal ions using a thermally-killed-Bacillus subtilis biosensor

The measurement of the biochemical oxygen demand (BOD) of an aqueous solution using a thermally-killed Bacillus subtilis BOD biosensor was unaffected by the presence of 5 mM of Al3+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Ni2+ and Pb2+ in the sample. In the presence of 5 mM of Zn2+, Mn2+ and Sn2+, the sensor over-estimated the BOD5 of the test samples by 12–68% compared with 13% under-estimation at the same concentration of Cu2+. The sensor completely and irreversibly lost its BOD sensing ability in the presence of 0.5 mM of Ag+ or Hg2+. Similar effect was observed with a living B. subtilis BOD biosensor. The interference of copper, manganese, stannous and zinc ions was effectively eliminated by dosing the substrate with 6.2 mM of ethylene diamine tetra-acetate (EDTA) or 5.8 mM of sodium diethyl dithiocarbamate (DDTC). The total concentration of mercury of the solution at which the sensor completely and irreversibly lost its BOD sensing characteristics was raised from 0.5 to 4.7 mM when the solution was dosed with 31.8 mM of NH4Cl; to 6 mM with 6.2 mM EDTA and to 3 mM with 5.8 mM DDTC. The total concentration of silver which would incapacitate the sensor was correspondingly raised to 9.7, 5 and 5.5 mM for the respective dosages and complexing agents. The sensor showed no response towards NH4Cl up to about 0.5 M and up to about 50 mM of EDTA and DDTC.