Evaluation of an electronic nose for the early detection of organic overload of anaerobic digesters

in Bioprocess and Biosystems Engineering (2012)

This study aims at the analysis of the utilization of an electronic nose (e-nose) to serve as a specific monitoring tool for anaerobic digestion process, especially for detecting organic overload. An ... [more ▼]

This study aims at the analysis of the utilization of an electronic nose (e-nose) to serve as a specific monitoring tool for anaerobic digestion process, especially for detecting organic overload. An array of non specific metal oxide semiconductor gas sensors were used to detect process faults due to organic overload events in twelve anaerobic semi-continuous reactors of 1.8 L. Three different load strategies were followed (i) a cautious organic load (1.3 gVS•L-1•day-1); (ii), an increasing load strategy (1.3 to 5.3 gVS∙L-1•day-1) and (iii) a cautious organic load with load pulses of up to 12 gVS•L-1•day-1. A first monitoring campaign was conducted with three different substrates : sucrose, maize oil, and a mix of sucrose/oil during 60 days. The second campaign was run with dry sugar beet pulp during 45 days. Hotelling's T²-value and upper control limit to a reference set of digesters fed with a cautious OLR (1.3 gVS•L-1•day-1), was used as indirect state variable of the reactors. Overload situations were identified by the e-nose apparatus with Hotelling’s T²-values at least 4-times higher in magnitude than the upper control limit of 23.7. These results confirmed that the e-nose technology appeared promising for online detection of process imbalances in the domain of anaerobic digestion. [less ▲]

Bioreactor hydrodynamic effect on Escherichia coli physiology: experimental results and stochastic simulations.

in Bioprocess and Biosystems Engineering (2005), 28(2), 131-7

A microorganism circulating in a bioreactor can be submitted to hydrodynamic conditions inducing a significant effect on its physiology. The mixing time exhibited by the stirred bioreactor and the ... [more ▼]

A microorganism circulating in a bioreactor can be submitted to hydrodynamic conditions inducing a significant effect on its physiology. The mixing time exhibited by the stirred bioreactor and the circulation of microorganisms are both involved in this reacting system. The mixing component determines the intensity of the concentration gradient and the circulation component determines the way in which the microorganism is exposed to this gradient. These two components linked to the experimental evaluation of microbial physiology can be analysed by a structured stochastic model in the case of a partitioned or "scale-down" reactor (SDR). A stochastic model indeed enables to simulate the mixing process as well as the circulation of microorganisms in SDRs. The superimposition of mixing and circulation processes determines the concentration profile experienced by a microorganism in the reactor. In the present case, the glucose concentration experienced by Escherichia coli has been modelled during a fed-batch culture. In this context, the use of a stochastic hydrodynamic model has permitted to point out an interesting feed pulse retardant effect in the SDRs. Nevertheless, the metabolic response of E. coli is not easy to interpret because of the possible simultaneous developments of overflow metabolism and mixed acid fermentation induced by the strong glucose concentration in the reactor. [less ▲]