TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The correction of estimate for the cellular concentration based on variation in conductivity of the extra-cellular medium (sigmae), is performed according to the formula (I).Ec(%) = E(%)asterisk3 (k / (2 + k)) (I)k = sigmai/sigmaeThe conductivity of intra-cellular medium (sigmai) can be considered constant (k) for a given microorganism.Alternately, the correction of estimate for cellular concentration is obtained from calibration curve derived from experimental data, by artificially varying the conductivity of extra-cellular medium (sigmae).The cell-free and cell-containing regions are within the same reactor or culture cell. The cell-free region is separated from the culture by a mesh having narrow opening. The separation between cell-free and cell-containing regions, is obtained by sedimentation. The cell-free region is obtained by depositing a non-biocompatible substance on the regions of reference, or by a treatment which makes the region of reference non-biocompatible. The cell-containing and cell-free regions are obtained from a culture sample which is divided into two equal samples. The samples are then introduced into identical vessels having identical sets of electrodes. The cells in one of the samples, are destroyed by ultra-sound, ultraviolet radiation, chemicals, heat treatment at high temperature or by applying high voltage electrical signals. Individual measurement is made in each region using a frontal stage for each set of electrodes, or by multiplexing a single frontal stage between each set of electrodes, to compare and/or process the measurements made with the probes.Sedimentation takes place in a measurement tube which is introduced with a preset volume of sludge. The rate of sedimentation is measured and its electrical impedance is measured during and after the end of sedimentation. The electrical impedance is measured by comparing sedimentation rate of supernatant and active sludge regions, to obtain a final estimator (E%) and the properties of biomass is measured according to the parameter of fc, Yo, d and A, where fc is frequency at which maximum imaginary part value is obtained which depends on the type of microorganism (Yo gives information on the properties of the stirred medium, d is dispersion of cells and shapes for the microorganism and A gives information about sedimented medium). EXAMPLE - None given.