Measurement of the activated sludge acclimation in a bi-substrate environment.
Integration of life sciences & engineering
Integration of Life Sciences & Engineering - Poster (T5-P)
Keywords: activated sludge, respirometry, biokinetic modelling,
Wastewater effluents in WWTP are characterized by their variability with time and substrate complexity. Biological sludge is able to adapt to these changing conditions for organic matter elimination in plant reactors. This work is focused on describing the experimental and data analysis method to study the biokinetic parameters evolution in the microorganisms acclimation [1].
Respirometric measurements with initial single substrate (ethanol, sodium acetate and sodium propionate) and a mixture of two substrates (ethanol+sodium acetate and ethanol+sodium propionate) at different concentrations are carried out. Biomass, coming from an urban wastewater treatment plant is acclimated to OECD synthetic wastewater, has been kept constant with ratio S0/X0 about 0.05 g COD/g TSS. The experimental set-up used in this work is a hybrid respirometer [2], consisting in an aerobic reactor of 3.8 L coupled to a respiration chamber of 0.3 L. The temperature of the reactors was kept at 20ºC. The dissolved oxygen present in both reactors is continuously recorded with two independent oxymeters and their values acquired by a computer.
In order to explain the evolution of the biokinetic parameters, a bi-substrate mathematical model has been proposed for the respirometer experiments. In this model, the dissolved oxygen is used as a state variable [3]. Parameters such as the specific growth rate of heterotrophic biomass, mu, heterotrophic saturation coefficient for the substrate, KS, and the heterotrophic biomass yield, YH, can be evaluated.
The results for single substrate experiments show a continuous increase of the specific growth rate constant probably due to a change in the enzymatic activity of the cells within the substrate injections. Additionally, the calculated heterotrophic yield remains constant along the experimental series which confirms that the mechanism of the substrate assimilation does not change with the experiments. Finally, the changes observed in the saturation coefficient could be explained considering a modification of the transport properties of the substrate into the biomass floc. When the bi-substrate media is analysed, the calculated biomass yields are similar to the single substrate experiments and the specific growth rate variations are slower than the single ones. As the experiments go forward, there is a bigger difference between the experimental values and the proposed model. These results suggest that the oxygen rate uptakes are not a linear combination of substrate consumption rates.
The authors wish to acknowledge the Conselleria d’Empresa, Universitat i Ciència de la Generalitat Valenciana for the financial support to this work under the project Ref GV05/190.
[1] Carvalho, G. Novais, J.M., Vanrolleghem, P.A., Wat. Sci. Tech., 45, 345-353 (2002).
[2] P.A. Vanrolleghem. Wat. Sci. Tech., 12, 237-246 (1998).
[3] Navarro-Laboulais, J., López F., Torregrosa, J.I., Cardona, S.C., Abad, A., Journal of Mathematical Chemistry, In Press (2006).
Presented Wednesday 19, 13:30 to 15:00, in session Integration of Life Sciences & Engineering - Poster (T5-P).
