Improving recognition of odors in a waste management plant by using electronic noses with different technologies, gas chromatography–mass spectrometry/olfactometry and dynamic olfactometry

Odor emissions from waste management plants have long been an environmental and economic issue, but only recently regional authorities in Italy are regulating this sector by imposing control and mitigation of the phenomenon. Electronic noses, initially developed as cheap, easy tools to detect volatiles, may have the required time-resolved coverage of the odor emission phenomenon in a cheap and feasible way with respect to chemical analysis of air. One crucial issue to resolve is to evaluate the discriminant capacity of a sensor array in-field and under working conditions. In this paper the authors have studied the responses of electronic noses of different technologies to odors emitted from a waste management plant, by integrating results obtained with dynamic olfactometry and gas chromatography–mass spectrometry/olfactometry, in the aim to implement a monitoring system and improve cleaner production technologies. Three most impacting odor sources in the waste management plant were detected: biogas, a by-product of mechanical treatment of municipal solid wastes, with low organic fraction and a sludge pressed and dehydrated from treatment of urban wastewater. The most odor impacting source was the sludge and the major responsible of the odor impacts were aromatics (in particular 1,3,5-trimethyl benzene), aliphatic hydrocarbons, terpenes and sulphur volatiles (methyl disulphide, carbon disulphide, dimethyltrisulphide). Ten Metal Oxide Semiconductors and 32 polymer/black carbon (Nano Composite Array) sensors in two electronic noses, were tested for discrimination source capabilities. Results of linear discriminant analysis and cross validation give 86.7% successful recognition for Metal Oxide Semiconductors, 53.3% for Nano Composite Array and 93.3% for a selection of sensors belonging to both technologies chosen according to the selectivity towards the odor active molecules. The containment of odors could also be achieved by spraying a specific product and monitoring the process using selected sensors of the arrays. The results of the in-field work demonstrate strengths and weaknesses of different construction technologies in the e-noses arrays, to characterize and monitor in-site and in real time odor emissions from waste management plants.