# Advancements and Prospects of Electronic Nose in Various Applications: A Comprehensive Review
## 3 Application Areas
### Environmental Monitoring
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Source of Malodor** & **Type of Sensor** & **Description and Results** & **Reference** \\ \hline Wastewater treatment plant & FOX 3000; 12 MOS & In this study, an electronic nose was used to monitor volatile compounds in post-treatment effluent. Samples were heated to 90 \({}^{\circ}\)C for analysis. Repeatability and reproducibility were \\ Wastewater treatment plant & Champaign, IL, USA) & The electronic nose demonstrated potential as a rapid alarm system for volatile compound detection in wastewater treatment, supporting reclaimed water production. & [134] \\ \hline Composite plant & 6 tin oxide sensors & This study entails real-time monitoring of compost facility odor emissions utilizing a self-made electronic nose composed of a sensor array with six tin oxide gas sensors. The system efficiently detects compost odor, estimates emission rates, and employs supervised data processing methods for recognition and classification. Principal component analysis facilitates the identification of compost odor, and calibration enables the estimation of odor emission rates. Furthermore, the study establishes a correlation between e-nose responses and odor concentration in the range of 0 to 1500 ou/m\({}^{3}\). The method showcases its effectiveness in detecting odor breakthroughs from the compost hall’s charcoal filters. & [135] \\ \hline Poultry farm & 12 sensors (MOS, hybrid, tin dioxide, tungsten oxide) & This paper introduces a portable electronic nose for measuring odors from livestock and poultry farms, suitable for lab and field use. The sensor array includes 14 gas sensors, a humidity sensor, and a temperature sensor for detecting farm odor compounds. The “Odour Expert” system employs AI for better odor control decisions. Field experiments from 14 farms show improved consistency between predicted odor strengths from the electronic nose and human panel perceptions, with accurate odor strength prediction using the e-nose (R = 0.93). The “Odour Expert” aids farmers in odor management. & [136] \\ \hline Rendering plant & 6 QMB, 6 MOS, chemical sensors (JIm Innovation, Tubingen, Germany) & DOSS system for real-time odor-monitoring from bio-filters. Developed by Danish institutes and industries in partnership. Utilizes QMB, MOS, and chemical sensors for data collection. Tests performed through field studies, showing high potential in odor concentration prediction (R = 0.93). Repeatability, stability, and effectiveness demonstrated in lab conditions and rendering plant tests. Promising for routine monitoring and process control of environmental odor impact. & [137] \\ \hline Building materials & KAMINA, multi-gas sensor on chip (Forschungszentrum Karlsruhe, Germany) & Study focuses on indoor air quality from building productsm System uses 38 gas sensors on chip. Calibration and testing combine gas sensor data with human panel odor assessments. Data model developed for odor intensity prediction. Humidity’s significant influence considered for future measurements. & [138] \\ \hline Piggery and abattoir emissions & 32 organic conducting polymer (CP) sensors (Kestrel, USA) & The electronic nose discriminated between four odor categories from a pig farm and an abattoir with an efficiency of approximately 80\%. & [139] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._process control, worker health preservation, and evaluating the efficiency of odor control systems. Notably, e-noses can act as alternatives or complementary tools to traditional analytical methods, offering cost-effective and real-time solutions. Research endeavors have shed light on e-noses' capability to identify pollution sources, enhance safety in industrial settings, and contribute to sustainable waste management practices. These advancements underscore the pivotal role that e-noses play in shaping our understanding of environmental odors and pollutants. As technology continues to evolve, e-noses are poised to become even more sophisticated and integrated into the fabric of smart cities and industries.