An automatic system for simultaneous monitoring of gas evolution in multiple closed vessels

A computerized automatic biogas activity monitoring (BAM) system for monitoring the production of biogas in closed vessels was developed. The system was used for determination of the specific biogas activity of granular sludge from an upflow anaerobic sludge blanket reactor. The biogas activity determined by the BAM system was compared with the biogas activity determined in parallel vials by gas chromatography as well as by manual pressure reading. There was no significant differences between the biogas activities determined by these three methods. The system consisted of a single pressure transducer which measured the pressure build-up through a motor driven multiport sampling valve in a series of up to 16 test vials. A standard PC computer equipped with an I/O card positions the multiport valve via an interface power circuit. The gas production of each vial was registered either in a differential or a cumulative form in a data file suitable for later numeric/graphic processing with standard spreadsheet software. It was shown that adequate mixing was required to avoid significant supersaturation of CO 2 in the liquid phase. When mixing was sufficient, the theoretical ratio of total pressure to methane partial pressure was shown to correspond well with experimental levels. In addition, a correlation factor between the total pressure and the methane partial pressure was theoretically deduced. Using this correlation factor, the methanogenic activity can be obtained directly from the BAM system readings. No significant differences were found between the methanogenic activity determined by the BAM system and by gas chromatography.