ESTIMATION OF MAXIMUM SPECIFIC GROWTH-RATE OF HETEROTROPHIC AND AUTOTROPHIC BIOMASS - A COMBINED TECHNIQUE OF MATHEMATICAL-MODELING AND BATCH CULTIVATIONS

Present methods for determination of kinetic and stoichiometric parame ters are mostly based on simple and rapid batch cultivation. An altern ative technique of mathematical simulation and a batch cultivation was proposed for estimation of maximum specific growth rates of heterotro phic and autotrophic microorganisms in activated sludge. Estimation of heterotrophic and autotrophic fractions in the biomass is based on ma thematical model calibration of continuously operated system. Maximum growth rates are then calculated from the maximum OUR measured in batc h tests. The proposed method was compared with a batch test cultivatio n based on an exponential growth of microorganisms when a proportion o f filtered wastewater is mixed together with a small proportion of bio mass and aerated in time. Comparing both methods, a disproportion betw een obtained results was found (mu(H,max) = 4 d(-1) from the proposed, and mu(H,max) = 10 d(-1) from the batch test method). An explanation of this observation was based on a hypothesis that under batch test co nditions (higher S-O/X(O) ratio) faster-growing microorganisms can be favoured in their growth. This phenomenon was mathematically simulated with a simplified model and confirmed. Therefore, it is recommended t hat some constants for mathematical modelling obtained from batch test s should be applied on continuously operated systems only with care.