Electronic nose Technology for reactor state and biogas quality assessment in anaerobic digestion

ECOBIOGA

Gas sensor array applied to the monitoring of biogas process

There is a lack of simple online monitoring system to control the performances of biogas reactors. The electronic nose technology appears to be an adapted device to deliver fast information about process disturbances in anaerobic reactors as it is adequate for online monitoring. In this study, twelve anaerobic mini-reactors were supervised with a home-made e-nose to observe process reaction in relation to organic overloads events. Usually, to avoid overload situations, on farms reactors are not fed at maximum load capacity, resulting in non optimized biogas production. The objective of the experiment was to determine if the gas sensors array feature can be related to the process state and if an indirect state variable, giving early warning of process faults, can be derived from the e-nose response. The results demonstrated that focusing on gas phase of anaerobic reactors with a simple device composed of an array of non-specific gas sensors helped in the warning of disorders of the anaerobic digestion process. Mahalanobis distance from a cautious feeding group (group of observations indicating a good process) can be used as an indirect variable to evaluate the intensity of the state disorder. Euclidean distance has been also calculated but it was less informative than the Mahalanobis distance.Optibioga

Multivariate process control charts based on reputed process indicators as an alternative to univariate control charts for the monitoring of anaerobic reactors submitted to acidosis

Optibioga

Electronic nose for reactor stability monitoring of an agricultural co-digestion biogas plant

peer reviewedEcobioga

Upscaling of an electronic nose for continuously stirred tank reactor stability monitoring from pilot-scale to real-scale agricultural co-digestion biogas plant

peer reviewedThis study investigated the use of an electronic nose for on-line anaerobic reactor state monitoring at the pilot-scale level and then upscaling to the full-scale level. E-nose indicator was compared to classical state indicators such as pH, alkalinity, volatile fatty acids concentration and to other gas phase compounds. Multivariate statistical process control method, based on principal component analysis and the Hotelling's T² statistics was used to derive an indicator representative of the reactor state. At the pilot-scale level, the e-nose indicator was relevant and could distinguish 3 process states: steady-state, transient and collapsing process. At the full-scale level, the e-nose indicator could provide the warning of the major disturbance whereas two slight disturbances were not detected and it gave one major false alarm. This work showed that gas phase relation with anaerobic process should be deeper investigated, as an e-nose could indicate the reactor state, focusing on the gas phase.Ecobioga

Ecobiogaz Projet - Biogas as a prerequisite to reduce both greenhouse gas and agriculture’s energy dependence: is it a profitable alternative ?

Ecobioga

Anaerobic digestion process monitoring: focus on the gas phase using electronic nose technology

Gas phase of four pilot-scale anaerobic reactors was monitored with a gas sensors array, also called electronic nose (e-nose) over three weeks. CH4, CO2, H2S, H2 concentration in the gas phase and biogas production rate were also measured. Reactors were exposed to process disturbances by doubling the organic loading rate and by decreasing the temperature from 38 to 32°C for 24 hours. During these tests, sludge pH and alkalinity were also measured. When organic loading was doubled, no changes were observed in pH and alkalinity, while hydrogen content in gas phase increased by 20% and took 8 hours to recover stable values of 130 ppm. Hydrogen sulphide also increased proportionally to organic loading of the reactors and took two days to return to stable values. Methane and carbon dioxide ratio changed from 1.2 to 0.95. No changes were observed during the temperature drop of the digesters apart from hydrogen concentration which increased sharply several hours. Electronic nose was able to detect variations in organic loading rates for the four anaerobic reactors, with increased signals for higher organic loadings of the pilots. Sensing of gas phase of anaerobic reactors was able to discriminate disorders of operating conditions of anaerobic reactors, especially organic loading.OPTIBIOGA