A mediator-type biosensor as a new approach to biochemical oxygen demand estimation

A novel biosensor for the determination of biochemical oxygen demand (BOD) was developed using potassium hexacyanoferrate(iii) [HCF(iii)] as a mediato r. The sensor element consists of a three-electrode system, with both worki ng and counter electrodes compactly integrated as a disposable using etchin g and electroplating processes. Pseudomonas fluorescens biovar V (isolated from a wastewater treatment plant) was immobilized on the surface of the wo rking electrode using poly(vinyl alcohol)-quaternized stilbazol (PVA-SbQ) p hotopolymer gel. Synthetic wastewater described by the Organization for Eco nomic Cooperation and Development (OECD) was used as a standard solution in stead of glucose-glutamic acid synthetic wastewater. The conditions of ampe rometric measurement were optimized at +600 mV (vs. Ag/AgCl) operating pote ntial, namely 40 mM HCF(iii) in a 0.1 M phosphate buffer (pH 7.0) at 20 deg reesC. The sensor response was linear from 15 up to 200 mg O l(-1) BOD. The response time was 15 min at 200 mg O l(-1) BOD. To demonstrate the wide me tabolic range of activity of the sensor, the sensor response to 14 substanc es in four categories of organic compounds was investigated. Further, it wa s shown that the response of this BOD sensor was not influenced in samples with low concentrations of dissolved oxygen under the measuring conditions used. For real wastewaters, the BOD values were determined using the sensor and compared favorably with those determined by the conventional BOD5 meth od.