ABSTRACT
New method for design of observers for biotechnological processes is proposed. The method consists of analytical derivation of the first integrals of the differential system, which describes the process. The first integrals connect unmeasurable variables with on-line measurable ones. The observers ' design is carried out with direct use of nonlinear model. The method is applied for classes of biotechnological processes. Two practical applications of the proposed method are done. A cultivation model for continuous process is used for biomass estimation, based on measurements of substrate concentration and a cultivation model of mixed culture system is used for cells and NH3 concentrations estimation.