Modeling aerobic carbon source degradation processes using titrimetric data and combined respirometric–titrimetric data: Experimental data and model structure

Abstract

Experimental data are presented that resulted from aerobic batch degradation experiments in activated sludge with simple carbon sources (acetate and dextrose) as substrates. Data collection was done using combined respirometric-titrimetric measurements. The respirometer consists of an open aerated vessel and a closed non-aerated respiration chamber for monitoring the oxygen uptake rate related to substrate degradation. The respirometer is combined with a titrimetric unit that keeps the pH of the activated sludge sample at a constant value by addition of acid and/or base. The experimental data clearly showed that the activated sludge bacteria react with consumption or production of protons during aerobic degradation of the two carbon sources under study. Thus, the cumulative amount of added acid and/or base could serve as a complementary information source on the degradation processes. For acetate, protons were consumed during aerobic degradation, whereas for dextrose protons were produced. For both carbon sources, a linear relationship was found between the amount of carbon source added and the amount of protons consumed (in case of acetate: 0.38 meq/mmol) or produced (in case of dextrose: 1.33 meq/mmol) during substrate degradation. A model taking into account substrate uptake, CO(2) production, and NH(3) uptake for biomass growth is proposed to describe the aerobic degradation of a C(x)H(y)O(z)-type carbon source. Theoretical evaluation of this model for reference parameters showed that the proton effect due to aerobic substrate degradation is a function of the pH of the liquid phase. The proposed model could describe the experimental observations with both carbon sources.

Quantification of the effect of CO2 transfer on titrimetric techniques used for the study of biological wastewater treatment processes

“…It should be noted that the Hp data (which showed apparent linearity during exogenous activity) provided no indication of the variations in CTR. Therefore the linearity check suggested in Gernaey et al (2002a) would not detect this variation. As such, making direct linkages between Hp data and biological activity, as reported possible by Feitkenhauer and Meyer (2004), without properly accounting for variation in CO 2 transfer, would in this case result in substantial errors when interpreting titrimetric data, as will be further discussed through modelling and simulation studies.…”

“…Consequently, the HPR signal is not constant, causing non-linearity in the Hp signal. Based on the linearity check of the Hp signal suggested in Gernaey et al (2002a), this violation of the assumption of constant background HPR would have been detected, leading to the titration data being discarded.…”

“…The hydrogen ion production rate observed for the aerobic degradation of acetic acid has been described by Gernaey et al (2002a) as:…”

“…The method is considered to be particularly useful for the study of nitrification as autotrophic activity has just a small impact on the concentration of dissolved inorganic carbon. Gernaey et al (2002a; applied the method to aerobic carbon oxidation processes. However, the method is expected to be applicable under certain experimental conditions that minimise the variation in CO 2 transfer during the experiment.…”

“…The increase in dissolved CO 2 concentration results in an increase in CTR and consequently, a change to the background hydrogen ion production rate. Gernaey et al (2002a; suggested a linearity check of the cumulative hydrogen ion production (Hp) data, and provided that the slopes of Hp obtained before and after an experiment are the same then the data obtained could be used for modelling purposes. However, direct experimental evidence to support the equivalence of linearity in the titration data and constant CO 2 stripping is still missing.…”