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Near‐infrared spectroscopy for process control and optimization of biogas plants

The application of near‐infrared spectroscopy for the process control of biogas plants was evaluated in this study. The study involves the generation of first calibrations using two instruments, a commercial Fourier transform near‐infrared instrument and a grating spectrometer‐based prototype. Both the current state of the prototype hardware and the methodology were examined. A biogas plant was sampled regularly during a time period of 43 wk. Classic analysis methods as well as spectroscopic methods were used for the examination of the samples. Calibrations for dry‐matter content and content of organic dry matter were developed for both devices using the partial least squares regression after preprocessing the spectra. It was evident that the application of near‐infrared spectroscopy using simplified and robust hardware on‐site of biogas plants is possible. It is feasible to find high deviations from the aspired consistence of the fermentation medium and some substrates with the presented calibrations.