Biosensors for nitrogen control in wastewaters

Biotech & Bioengineering

Petersen

Comeau

et al. 2002

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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Biotech & Bioengineering

Petersen

Comeau

et al. 2002

“…In that case, monitoring the acid and/or base consumption rate(s), needed to keep the pH constant, provides the rate of proton formation or consumption related to the biological reactions. This titrimetric technique has already been applied in dierent studies of biological nitrogen removal processes in activated sludge (Bogaert et al, 1997;Gernaey et al, 1998;Massone et al, 1996;Ramadori et al, 1980).…”

Section: Introductionmentioning

confidence: 99%

Modeling aerobic carbon source degradation processes using titrimetric data and combined respirometric–titrimetric data: Structural and practical identifiability

Biotech & Bioengineering

Petersen

Dochain

et al. 2002

The structural and practical identifiability of a model for description of respirometric-titrimetric data derived from aerobic batch substrate degradation experiments of a C(x)H(y)O(z) carbon source with activated sludge was evaluated. The model processes needed to describe titrimetric data included substrate uptake, CO(2) production, and NH(3) uptake for biomass growth. The structural identifiability was studied using the Taylor series method and a recently proposed generalization method. It showed that combining respirometric and titrimetric data allows structural identifiability of one extra parameter combination, the biomass yield, Y(H), compared to estimation on separate data sets, on condition that the nitrogen fraction in biomass (i(XB)) is known. However, data from short-term batch substrate degradation experiments were not sufficiently informative to allow practical identification of all structurally identifiable parameters. Combining respirometry and titrimetry resulted in improvements of parameter confidence intervals compared to estimation on separate respirometric or titrimetric data sets. However, the level of the improvement seems to be substrate dependent: parameter confidence intervals improved considerably more for dextrose than for acetate degradation models. Noteworthy is the finding that the half-saturation substrate concentrations can be different depending on whether they are estimated from respirometric or titrimetric data. Moreover, this difference appears to be dependent on the carbon source considered: for dextrose, titrimetry-based K(S) values are higher than respirometry-based values while for acetate the opposite was found. It was hypothesized that this can be explained by the different point in cell metabolism where the proton production or consumption takes place, leading to a corresponding difference in timing between pH effect and oxygen consumption. Finally, the biomass yield Y(H) and the nitrogen content of the biomass i(XB) could be estimated from combined respirometric-titrimetric data obtained with addition of a known amount of carbon source. Y(H) can also be estimated from r(O) data when the initial substrate concentration S(S)(0) is known. The values found correspond to values reported in literature, but, interestingly, also seem able to reflect the occurrence of storage processes when pulses of acetate and dextrose are added.

“…17,20,24 Basically this titration technique quanti®es the protons formed during nitri®ca-tion using a pH controller, which will continuously compensate the protons produced by adding equivalent amounts of base to a sludge sample. Sludge was sampled from two different plants: a municipal wastewater treatment plant (WWTP) (Zwalm, Belgium; 2±3 g dm À3 suspended solids (SS)) and a plant treating the wastewater of a hospital (Middelares, Gent, Belgium; 4±5 g dm À3 SS).…”

Section: Data Collectionmentioning

confidence: 99%

A new pH-based procedure to model toxic effects on nitrifiers in activated sludge

J. Chem. Technol. Biotechnol.

Maffei

Vanrolleghem

et al. 1999

A combination of a titration experiment and a biokinetic parameter estimation procedure is proposed as an experimental tool to study the kinetics of NH 4 -oxidizing bacteria in activated sludge. The method was used to quantify the effect of low concentrations of a toxic compound on the maximum substrate removal capacity and the substrate af®nity constant (K NH ) of NH 4 -oxidizing bacteria in activated sludge samples. Experiments in the presence of increasing concentrations of a toxic compound (CN À , 3,5-DCP, Cu 2 and phenol) were performed with nitrifying activated sludge samples obtained from two full-scale wastewater treatment plants. The repeatability of the proposed procedure was found to be suf®cient to deduce trends in the behavior of the NH 4 -N-oxidizing bacteria based on one series of experiments with increasing toxicant concentrations. The experimental results showed that the two sludge samples reacted completely differently in the presence of a certain concentration of the same toxic compound. For phenol, the shape of the titration curves did not correspond any longer to a simple Monod model. In this case, titration curves could be described by a model including both nitri®cation inhibition by phenol and degradation of the phenol by heterotrophic bacteria.