Biogas Production Regime for In-Storage-Psychrophilic- Anaerobic-Digestion

In-Storage-Psychrophilic-Anaerobic-Digestion (ISPAD) is a technology which allows livestock producers to operate an anaerobic digester with minimum technological knowhow and for the cost of a conventional storage cover. Nevertheless, the system is exposed to ambient temperatures and biogas production is expected to vary with climatic conditions. The objective of the present project was therefore to design an automated biogas composition monitoring system for ISPAD and analyse the biogas composition produced during the time span of the project. The challenges in designing this monitoring system were: respecting the concentration range expected for CH4 and CO2, building air-tightness gas lines to prevent contamination and corrosion of the electronic devices inside the metallic box housing the monitoring system and; automating the gas line flushing operations. In the laboratory, the system was designed, calibrated and validated using gas samples of known CO2 and CH4 concentrations. Once connected to a field ISPAD system treating grower hog manure, the system was further validated by feeding CO2 and CH4 mixtures of known composition and by sampling the ISPAD biogas for gas chromatography analyses. Both in the laboratory and field, the automated system read CO2 and CH4 concentrations with a maximum error of 16 and 9%, respectively. Although a monthly calibration is recommended, the sensors demonstrated very little drift over a period of up to 55 days. Once validated, the automated monitoring system was able to measure biogas CO2 and CH4 concentrations and fluctuations respecting fully all ISPAD operations. i