Monitoring of a biogas process using electronic gas sensors and near-infrared spectroscopy (NIR)

The use of electronic gas sensors and near-infrared spectroscopy (NIR) to m onitor the dynamics in a biogas process was evaluated using multivariate da ta analysis. The digester, a completely stirred 81 tank reactor fed with a mixture of cellulose, albumin and minerals, was exposed to an overload of g lucose after which monitoring of electronic gas sensor responses, NIR spect ra as well as traditional chemical variables and analysis of microbial comm unity structure were done. The responses from an array of electronic gas se nsors consisting of MOS and MOSFET-sensors were correlated against volatile compounds in the headspace using partial least square (PLS) regressions. T he root mean square error of prediction (RMSEP) was 0.15 g/l for acetate in the range of 0.14-1.72 g/l and the RMSEP for methane was 2.3% in the range of 27-73%. Selected wavelengths from the second derivative of the original NIR spectra (400-2500 nm) resulted in a PLS-model for predicting microbial biomass, measured as total phospholipid fatty acids, with a RMSEP of 9 nmo l/ml in the range of 163-293 nmol/ml. The NIR model developed for acetate h ad a RMSEP of 0.20 g/l within the range of 0.14-1.72 g/l. The results clear ly show that both NIR and an array of electronic gas sensors can provide si multaneous non-invasive in situ monitoring of important process variables i n anaerobic digesters.