Aerial Mapping of Odorous Gases in a Wastewater Treatment Plant Using a Small Drone

Abstract

Wastewater treatment plants (WWTPs) are sources of greenhouse gases, hazardous air pollutants and offensive odors. These emissions can have negative repercussions in and around the plant, degrading the quality of life of surrounding neighborhoods, damaging the environment, and reducing employee’s overall job satisfaction. Current monitoring methodologies based on fixed gas detectors and sporadic olfactometric measurements (human panels) do not allow for an accurate spatial representation of such emissions. In this paper we use a small drone equipped with an array of electrochemical and metal oxide (MOX) sensors for mapping odorous gases in a mid-sized WWTP. An innovative sampling system based on two (10 m long) flexible tubes hanging from the drone allowed near-source sampling from a safe distance with negligible influence from the downwash of the drone’s propellers. The proposed platform is very convenient for monitoring hard-to-reach emission sources, such as the plant’s deodorization chimney, which turned out to be responsible for the strongest odor emissions. The geo-localized measurements visualized in the form of a two-dimensional (2D) gas concentration map revealed the main emission hotspots where abatement solutions were needed. A principal component analysis (PCA) of the multivariate sensor signals suggests that the proposed system can also be used to trace which emission source is responsible for a certain measurement.

Gas source localization and mapping with mobile robots: A review

“…Reproduced from Arroyo et al (2022) with permission from Elsevier. (d) DJI Matrice 600 Pro equipped E‐nose using suspended 10 m sampling tube, adapted from Burgués et al (2021). (a,b,d) licensed under CC BY 4.0 ( https://creativecommons.org/licenses/by/4.0/).…”

“…Mini drones are suited to applications which require fewer gas concentration measurements to be collected quickly over very large areas, or sampling in environments and locations which would be out of reach for UGVs. Examples include, measuring volcanic gas emissions (Arellano et al, 2019), air pollution monitoring over areas of open cast mining (Ren et al, 2019), monitoring the emissions from maritime vessels (Yuan et al, 2020), locating and quantifying hazardous chemical releases (Hutchinson et al, 2019), and localizing and mapping emission hotspots from civil waste treatment facilities (Burgués et al, 2021; Fjelsted et al, 2019).…”

“…To avoid this, long sampling tubes can be suspended from the UAV, placing the inlet far outside of the region of wake. A 10 m suspended sampling tube was used by Burgués et al (2021) for gas distribution mapping of a water treatment plant (Figure 5d). Although accurate point measurements could be achieved under ideal environmental conditions, the tube would be blown from its vertical position by wind and would not be usable in cluttered environments where the tube could become tangled with obstacles during navigation.…”

Odors Emitted from Biological Waste and Wastewater Treatment Plants: A Mini-Review

“…On the other hand, many works dealing with odor and odorant emissions from WWTPs focused on the design and development of the so-called electronic noses in order to facilitate and automate odor emission quantification and, consequently, odor emission dispersion [71][72][73]. Typically, the compounds monitored by this kind of system are VOCs, VSCs, and nitrogen compounds, which are the typical odor precursors found in WWTP gaseous emissions.…”

“…Together with odor concentration measurements, the main aim is to be able to correlate the concentration of different groups of odorant compounds with the odor concentration to finally obtain an electronic system independent of human panels that enables odor emission assessment in WWTPs. In this sense, Burgués et al (2021) developed an e-nose mounted on a small drone which was capable of generating realtime aerial maps of the odor emissions in WWTPs, using a set of 21 gas sensors together with four environmental parameters sensors to highly correlate the concentrations of H 2 S, NH 3 , mercaptans, amines, and different VOCs with odor concentrations measured by the dynamic olfactometry of field samples [71,72]. As stated before, the conclusion is that electronic noses are helpful tools for odor impact assessment; however, it is also clear that maximizing the odor information in terms of olfactometric analysis together with powerful analysis by GC-MS and electronic noses is the way to follow for a proper odor emission characterization [26].…”