This chapter contains information about application of the electronic nose type instruments to evaluation of ambient air odour quality connected with such sectors of human activity as municipal landfills or sewage treatment plants. The authors present potential sources of emission from these sectors, characterize the chemical compounds responsible for presence of unpleasant odours, describe the influence of those compounds on human health and related discomfort. Legal aspects pertaining to admissible odour concentration levels in selected countries are also presented. The chapter describes instrumental and sensory methods utilized for determination of odour concentration, odour intensity, or hedonic quality. The chemical sensors potentially and currently employed in the electronic nose type devices are also characterized. Moreover, the future prospects of application of the electronic nose instruments to evaluation of ambient air with respect to odour nuisance are discussed.
TopIntroduction
Progress in economic and industrial development significantly contributes to increased emission of pollutants to ambient air. Industrial plants, such as production plants, refineries, meat processing plants, breweries and distilleries, agricultural plants, metallurgical industry, and municipal plants: landfills, sewage treatment plants and solid waste processing plants generate significant amount of environmentally hazardous pollutants characterized by different physical and chemical properties. Such situation occurs despite widespread implementation of modern technologies in the aforementioned plants aimed at limitation of malodorous substances emission to the environment. Negative impact of these compounds can results from both intrinsic properties of individual chemicals as well as synergistic amplification of hazardous properties of various interacting chemical compounds (Byliński, Lewkowska, Gębicki, Dymerski, & Namieśnik, 2016). In some cases individual substances reveal small impact on particular elements of biotic and abiotic environment, nevertheless, their influence can significantly increase upon presence of other, interacting compounds. Among many different chemical compounds the odours (odorous compounds) play a significant role. The odours are volatile chemical organic and inorganic compounds sensed by animals and humans via olfactory receptors at very low concentrations and identified by brain as unpleasant sensations. The compounds characterized by unpleasant odour include:
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Inorganic Compounds: Hydrogen sulphide, ammonia, Sulphur dioxide, nitrogen oxide, hydrogen fluoride and hydrogen arsenide,
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Organic Compounds: Thiols, sulphides and disulphides, amines, carboxylic acids, aldehydes, ketones, aromatic hydrocarbons.
General definition identifies the odour as an individual chemical compound or a mixture of chemical compounds containing osmophoric groups in their structure. Table 1 presents the exemplary osmophoric groups and names of the chemical compounds containing these groups.
Table 1. Exemplary osmophoric groups
Reduction of emission of the odorous compounds becomes a priority for these fields of industry, which are responsible for their emission to ambient air. This reduction can consist in:
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Prevention of odorous compounds emission,
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Implementation of deodorization systems in already existing plants,
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Appropriate design and location of new-built facilities.
Irrespective of applied technology resulting in limitation of odours emission it is necessary to check (monitor) effectiveness of deodorization via measurement of odour intensity or odour concentration at inlet and outlet of an installation. One of the most popular methods of odour measurement, apart from olfactometric techniques, are instrumental techniques including electronic nose method. This technique, similarly to the olfactometric methods, utilizes holistic analysis without a need for identification of particular components contributing to a resultant odour. It belongs to a group of dynamically developing instrumental techniques and is more and more frequently employed to monitoring of unpleasant odours originating from different fields of human activity.