Abstract
Systems that are made of several low-cost gas sensors with automatic gas sampling may have the potential to serve as reliable fast methane analyzers. However, there is a lack of reports about such types of systems evaluated under field conditions. Here, we developed a continuous methane monitoring system with automated gas sampling unit using low-cost gas sensors, TGS 2611 and MQ-4, that use a simple cloud-based data acquisition platform. We verified the consistency, repeatability, and reproducibility of the data obtained by TGS 2611 and MQ-4 low-cost gas sensors by measuring high- and low-concentration methane samples. The normalized root-mean-square errors (NRMSEs) of the samples with high methane concentrations, [CH4] of 3, 4, 6, and 7%, were 0.0788, 0.0696, 0.1198, and 0.0719 for the TGS 2611 sensor, respectively, and were confirmed using a gas chromatograph as a reference analyzer. The NRMSEs of the samples with low [CH4] of 0.096, 0.145, 0.193, and 0.241% measured by the TGS 2611 sensor were 0.0641, 0.1749, 0.0157, and 0.1613, whereas those NRMSEs of the same concentrations measured by the MQ-4 sensor were 0.3143, 0.5766, 0.6301, and 0.6859, respectively. Laboratory-scale anaerobic digesters were tested using the developed system. The anaerobic digesters were continuously operated for 2 months, demonstrating the potential use of sensors for detecting and monitoring methane in the field level application. This study utilized a unique way to combine the advantages of low-cost sensors and develop a reliable monitoring system by minimizing drawbacks of low-cost sensors.
Highlights
Air quality monitoring has become a critical requirement due to the current rise in health issues associated with air pollution, climate change, and impaired quality of life (Bentayeb et al, 2015; Manisalidis et al, 2020; Pascal et al, 2013; Raaschou-Nielsen et al, 2016; Wu et al, 2016)
We developed a low-cost gas sensor system for monitoring methane concentration that uses a simple cloudbased data acquisition platform
We tested the performance of the low-cost methane monitoring system by combining it with anaerobic digesters
Summary
Air quality monitoring has become a critical requirement due to the current rise in health issues associated with air pollution, climate change, and impaired quality of life (Bentayeb et al, 2015; Manisalidis et al, 2020; Pascal et al, 2013; Raaschou-Nielsen et al, 2016; Wu et al, 2016). With the concern about the direct impact of methane (CH4) on climate change and human health (Isaksen et al, 2014), it is important to continuously monitor atmospheric methane spatially and temporally. Gas samples can be detected using various analyzers, including gas chromatography-flame ionization detectors (GCFID), Fourier transform infrared (FTIR) spectroscopic methods and optical gas imaging (Oliver, 2019). These measurement techniques require expensive instruments and technical knowledge to operate them, and the measurements are carried out intermittently owing to the cost of the analysis. Many detection and measurement technologies exist, each method has its limitations and only a few available technologies have real-time, continuous monitoring capabilities (Hu et al, 2014)
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