Abstract

Considering the global climate change, the efficient use of clean and renewable sources of energy is one of the key research areas. In this context, the biological production of methane and other combustible biogas produced by anaerobic fermentation of organic wastes is gaining growing importance. These fermentation processes attract more and more interest mainly due to the possibility to use different types of residues like food waste, dairy wastes and many other organic wastes as feeding substrates. However, efficient biomass conversion to biogas is only possible if the process parameters taking direct influence on the fermentation process are continuously and reliably monitored. This allows efficient process control. One of such key process parameters are the volatile fatty acids (acetic, propionic, butanoic) formed during the biomass conversion process. The reliable monitoring of such organic acids and other volatile organic compounds (VOCs) gives valuable information and their analysis even at low concentrations (<2000 ppm) allows to model the actual microbial state and to adapt the feeding to keep their concentration and their inhibiting influence on the fermentation process low.

Conventionally, the analysis of the organic acid composition in anaerobic fermentation processes is done by sophisticated methods like gas chromatography [1], infrared spectroscopy [2], and high pressure liquid chromatography (HPLC) [3]. However, the major disadvantages of these methods are their complicated and time consuming sample pre-treatment routines and high costs.

In this paper, an automated measuring system developed by combining a silicon rubber membrane based carrier gas probe (Fig. 1) with a thermo-cyclically operated metal oxide gas sensor array [4] is introduced. This automated system might enable in-situ monitoring of different VOCs developing during the bio-fermentation processes in time periods of about one hour.

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