Researchers develop “electronic nose” to monitor odors at wastewater treatment plants
Researchers from Spain have built a portable electronic nose (e-nose) that is almost as sharp as a human nose at detecting odors from wastewater treatment plants. Combined with a drone, the lightweight e-nose can measure the concentration of various odors, predict odor intensity, and create a real-time odor map of the plant for management purposes.
Typically, odors at a wastewater treatment plant are measured using dynamic olfactometry, in which a group of people sniffs and evaluates air bags collected from the plant. Although this method is considered the gold standard, the process is expensive, slow and infrequent, which prevents operators from responding quickly to problems or identifying the source of the stench.
“I live two kilometers from a wastewater treatment plant, and sometimes you can’t even open a window because the smell is terrible. We must not underestimate the impact on the quality of life of people living near these facilities, and there are physical and psychological effects from exposure to unpleasant odors”
To better control odor emissions from treatment plants, Marco and his team developed a portable electronic nose for real-time monitoring and data visualization using artificial intelligence. The team collected air bags from plants and trained the e-nose to “sniff out” pungent chemicals such as hydrogen sulfide, ammonia and sulfur dioxide, which smell like rotten eggs, urine and burnt matches, respectively.
The e-nose is also equipped with a carbon dioxide sensor and a bacterial activity indicator. In laboratory conditions, the e-nose performs almost as well as a human. The researchers then attached the 1.3 kg e-nose to a drone and flew it over a medium-sized wastewater treatment plant in southern Spain from January to June. Flying over various facilities at the plant, the “nose drone” drew in air through a ten-meter tube and analyzed it in the sensor chamber.
“The difficulty of measuring odor lies in the fact that it is human perception, and it is not entirely well defined. We are not only trying to quantify individual components of emissions, but also to predict the intensity of odors as perceived by people”
The results showed that the drone-mounted e-nose can be used to monitor wastewater odor. When analyzing the same air samples in field tests, 10 of 13 e-nose measurements matched the assessments of a human panel. Thanks to the drone’s mobility and the artificial intelligence algorithm, the team also mapped the temporal and spatial concentration of the odor and, for the first time, predicted odor intensity based on drone measurements.
Marco said: “We are very pleased with the results, but additional testing is needed to make the device more reliable for use at a real plant.” The team plans to reduce the weight of the e-nose and develop a standardized process for this method. They also want to further optimize the device against the effects of temperature, humidity and other environmental conditions that could affect accuracy.
“This work may also be relevant to other facilities, such as landfills, composting plants, or even large cattle and pig farms, which are known to produce all kinds of unpleasant odors”
“Quantifying odor emissions at wastewater treatment plants is key to minimizing the impact of odors on surrounding communities. Odor measurements at treatment plants are usually performed either with expensive and intermittent olfactometric hydrogen sulfide detectors or with fixed electronic noses. We propose a portable, lightweight electronic nose specifically designed for real-time odor monitoring at wastewater treatment plants using small drones,” the study says.
The so-called RHINOS electronic nose makes it possible to measure odors with high spatial resolution, and its accuracy is only slightly lower than that of dynamic olfactometry. The device was calibrated using odor samples collected at a wastewater treatment plant in Spain over six months and verified at the same plant three weeks after calibration.
The promising results confirm that the proposed tool is suitable for identifying the odor sources with the highest emissions, which can serve as a useful guide for plant managers in controlling and eliminating odors.
Electronic noses, also called sensor arrays or instrumental odor monitoring systems (IOMS), are currently considered the most promising tools for monitoring environmental odors. An electronic nose is a chemical measurement system based on multiple non-specific chemical sensors (usually 5 to 20 sensors) with additional sensitivity to a wide range of volatile organic compounds and inorganic gases.
The most commonly used sensors in environmental monitoring are metal oxide semiconductors, although existing systems increasingly include additional semi-specific sensors (such as electrochemical cells) for H2S (hydrogen sulfide) or NH3 (ammonia). By considering the odor mixture as a whole rather than its individual components, the device can correlate better with odor concentration than any other instrumental method.
