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.