THE INFLUENCE OF ELECTRODE POLARIZATION ON DIELECTRIC SPECTRA, WITH SPECIAL REFERENCE TO CAPACITIVE BIOMASS MEASUREMENTS - I - QUANTIFYING THE EFFECTS ON ELECTRODE POLARIZATION OF FACTORS LIKELY TO OCCUR DURING FERMENTATIONS

Electrode polarisation can interfere significantly with the measuremen t of the dielectric properties of biological systems, and in particula r with the dielectric estimation of microbial biomass. We show that el ectrode polarisation can be modelled by a power law and that the param eters of this model can be simply modified to give reliable and intuit ive measures of the magnitude (C-L(P)) and rate of fall of polarisatio n with increasing frequency ((h)f). Importantly and surprisingly, alth ough the magnitude of electrode polarisation depends strongly on the c onductance of the medium and the material of the electrodes, above a c ertain value of medium conductance (of some 3-7 mS, conductivity = 3.7 -8.7 mS cm(-1)), the value of (h)f is a constant and independent of th e conductance of the medium. It is also independent of the electrode m etal in the probes, which probe was used, the ionic and other componen ts in the medium, the electrode interface current density, the cell co nstant, the presence of fouling materials and whether or not any elect rolytic cleaning pulses had been applied. This permits one simply to c orrect for the electrode polarisation present in dielectric spectra an d which may sometimes be seen during dielectric biomass measurements. (C) 1998 Elsevier Science S.A. All rights reserved.