Application of a Hybrid Respirometric Technique to the Characterization of an Industrial Wastewater

Two respirometric principles are combined in an experimental setup based on a laboratory scale batch reactor and applied to the characterization of activated sludge and wastewater. In the first respirometric principle the temporary disturbance of the dissolved oxygen concentration in the reactor is used to estimate the respiration rate. To this end, the oxygen mass-transfer must be calculated and a dedicated mass-transfer estimation method was developed. In the other principle the respiration rate is calculated directly from the mass balance of dissolved oxygen over a closed vessel through which the sludge is circulated. A special arrangement eliminates the requirement for two oxygen probes, making the measurement more reliable. Since both respiration rate measurements are applied simultaneously to the same reactor, two independent outputs are obtained that can be compared and evaluated. This hybrid technique was applied to the characterization of wastewater and activated sludge of a plant treating the effluent of a potato starch mill. The procedure includes the addition of wastewater samples to activated sludge, collection of the respiration rate data and evaluation of the measurements by estimation of biokinetic parameters. Special attention is given to the ratio of the initial substrate to the initial biomass concentration applied in the experiments. It has been shown that the two principles can easily be implemented in the hybrid technique. Respirograms obtained with the two principles correspond reasonably well, but there is some disagreement between the results when the respiration rate is used to determine biokinetic model parameters.