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

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

Passive elimination of correlated amplitude fluctuations in ultrabroadband supercontinua from highly nonlinear fibers by three-wave mixing

The nonlinear transformation of fluctuations by frequency broadening is found to produce strong anti-correlations in the spectral output. This effect is investigated by dispersive Fourier transform measurements. We exploit the anti-correlations in order to cancel the intensity noise in a subsequent sum-frequency mixing step. This principle allows for the generation of tunable visible pulses by cascaded nonlinear mixing whilst maintaining the same intensity noise performance as the input pulses. In addition, we demonstrate that the power fluctuations occurring in the process of passive stabilization of the carrier-envelope phase locking via difference frequency generation may be cancelled by an analogous strategy.publishe

Passive elimination of correlated amplitude fluctuations in ultrabroadband supercontinua from highly nonlinear fibers by three-wave mixing

The nonlinear transformation of fluctuations by frequency broadening is found to produce strong anti-correlations in the spectral output. This effect is investigated by dispersive Fourier transform measurements. We exploit the anti-correlations in order to cancel the intensity noise in a subsequent sum-frequency mixing step. This principle allows for the generation of tunable visible pulses by cascaded nonlinear mixing whilst maintaining the same intensity noise performance as the input pulses. In addition, we demonstrate that the power fluctuations occurring in the process of passive stabilization of the carrier-envelope phase locking via difference frequency generation may be cancelled by an analogous strategy.</jats:p