Assessment of the applicability of a low-cost sensor–based methane monitoring system for continuous multi-channel sampling

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.

Diseño técnico de un sistema de cuantificación de metano portable y de bajo costo

“…Cabe resaltar que el uso de una cápsula para disminuir el espacio entre el sensor y el gas de calibración mejora en gran medida la linealidad de la medición, logrando superar ampliamente el límite de medición de fábrica en relación con otros métodos o técnicas de cuantificación. Esto representa una mejora con respecto a casos de uso de sensores de la serie MQ-4 para la medición de metano reportados en la literatura, como es el caso de (19), que presentó incertidumbres al momento de registrar datos coherentes, pues el sensor MQ-4 no pudo proporcionar valores aceptables debido a su limitación de detección y mostró una respuesta bruta limitada a las posteriores concentraciones de metano. A lo anterior se suma la opción de revisar la concentración del metano para asegurar la calidad de combustión del biogás.…”

“…Si se sabe que el gas tiene un concentración alta de metano, se recomienda diluirlo o comenzar con una concentración baja de metano pues, de lo contrario, el sensor puede saturarse, lo cual evita que este realice mediciones. Si esto ocurre, se debe dejar reposar el sensor de 30 minutos a 1 hora al aire libre para que se dispersen las trazas del gas de calibración (19).…”

Utilization of a Low-Cost Sensor Array for Mobile Methane Monitoring

“…However, these tools are not without drawbacks, as they require costly equipment that can require extensive training and expertise to run correctly. Alternatively, over the past decade, studies have pioneered the use of low-cost sensors (LCS) to accurately quantify methane concentrations in lab studies [ 14 , 15 , 16 ], stationary deployments in urban areas [ 17 , 18 , 19 ], and fence line monitoring [ 20 ]. Other studies have leveraged the combination of low-cost sensors with machine learning methods to specify and predict individual VOC concentrations in stationary laboratory and field experiments with high fidelity [ 21 , 22 ].…”

Simultaneous Monitoring of ppmv Level Methane and ppbv Level VOCs Near Industrial Sources Using a Real-Time GC

“…Recently, a continuous monitoring system for methane and total NMHC measurements at the ppmv level has been developed (Wang et al, 2018). Furthermore, a low-cost and multichannel instrument based on sensor technology that targets speci cally for methane monitoring was also reported (Nagahage et al, 2021). As for individual environmental VOC analysis at the low ppb level, the compendium methods published by the U.S. EPA (Environment Protection Agency) (Winberry et al, 1988) are the most reliable methods that have been veri ed by numerous researchers worldwide for decades (McClenny et al, 2002).…”