Publications

Instrumental Odour Monitoring Systems are often based on gas sensor arrays, or eventually on single sensor solutions for major odorants. In this work, we investigate the use of a portable Ion Mobility Spectrometer (IMS) as an Instrumental Odour Monitoring System (IOMS) for monitoring odorous emissions from wastewater treatment plants (WWTPs). This preliminary study was carried out on two plants in Pinedo (Valencia), i.e., P1 and P2. Three field campaigns (JanuaryJune-July) captured seasonal and wastewater variations, employing chemometric analysis and Principal Component Analysis (PCA) to distinguish Water line and Sludge line emissions. Random Forest (RF) and Partial Least Squares Discriminant Analysis (PLS-DA) were used to develop an odour classification model. External validation achieved an 87% accuracy for P1 July and results for P2 January-June. These results prove the IMS potential to be used for enhanced odour emission classification, possibly in combination with other monitoring techniques.

JTD Keywords: Discrimination, Ioms, Odour classification, Pc, Pls-da, Source

Abstract Definitions of the limit of detection (LOD) based on the probability of false positive and/or false negative errors have been proposed over the past years. Although such definitions are straightforward and valid for any kind of analytical system, proposed methodologies to estimate the LOD are usually simplified to signals with Gaussian noise. Additionally, there is a general misconception that two systems with the same LOD provide the same amount of information on the source regardless of the prior probability of presenting a blank/analyte sample. Based upon an analogy between an analytical system and a binary communication channel, in this paper we show that the amount of information that can be extracted from an analytical system depends on the probability of presenting the two different possible states. We propose a new definition of LOD utilizing information theory tools that deals with noise of any kind and allows the introduction of prior knowledge easily. Unlike most traditional LOD estimation approaches, the proposed definition is based on the amount of information that the chemical instrumentation system provides on the chemical information source. Our findings indicate that the benchmark of analytical systems based on the ability to provide information about the presence/absence of the analyte (our proposed approach) is a more general and proper framework, while converging to the usual values when dealing with Gaussian noise.

JTD Keywords: Limit of detection, Information theory, Mutual information, Heteroscedasticity, False positive/negative errors, Gas discrimination and quantification

In this paper, we address the task of gas distribution modeling in scenarios where multiple heterogeneous compounds are present. Gas distribution modeling is particularly useful in emission monitoring applications where spatial representations of the gaseous patches can be used to identify emission hot spots. In realistic environments, the presence of multiple chemicals is expected and therefore, gas discrimination has to be incorporated in the modeling process. The approach presented in this work addresses the task of gas distribution modeling by combining different non selective gas sensors. Gas discrimination is addressed with an open sampling system, composed by an array of metal oxide sensors and a probabilistic algorithm tailored to uncontrolled environments. For each of the identified compounds, the mapping algorithm generates a calibrated gas distribution model using the classification uncertainty and the concentration readings acquired with a photo ionization detector. The meta parameters of the proposed modeling algorithm are automatically learned from the data. The approach was validated with a gas sensitive robot patrolling outdoor and indoor scenarios, where two different chemicals were released simultaneously. The experimental results show that the generated multi compound maps can be used to accurately predict the location of emitting gas sources.

JTD Keywords: Environmental monitoring, Gas discrimination, Gas distribution mapping, Service robots, Open sampling systems, PID, Metal oxide sensors