Anaerobic digestion of maize and cellulose under thermophilic and mesophilic conditions - A comparative study

The aim of this study was to advance in understanding of digestion process of energy crops. Cellulose and maize silage were fermented in batch mode at mesophilic (38 degrees C) and thermophilic (55 degrees C) conditions and corresponding organic loads of 5.5 +/- 0.2 kgVS/m(3), 11.2 +/- 0.3 kgVS/m(3) and 16.7 +/- 0.4 kgVS/m(3). For both substrates more stable and faster digestion took place at 38 C. Due to complex structure maize degradation was characterized by varying digestion rate and longer total digestion time resulting form breakdown of hard-degradable fractions. The digestion retard at increased OLRs of cellulose and lower degradation level obtained for all cellulose series confirm a higher overloading potential for systems dealing with single-component-substrates but also the enhanced sensitivity of such systems to any inconvenient digestion conditions. Based on observed patterns of volatile fatty acids and oxidation-reduction potential, different fermentation mechanisms can be concluded for cellulose and maize, but also for different temperature modes. Conversion of maize at highly reductive conditions with increased concentrations of butyric acid was accompanied by much higher activity of hydrogenotrophic methanogens than for cellulose digestion. Two factors showed a strong potential to influence test results: an insufficient VS content of inoculum, which caused reduced biogas yields, and a high natural biodiversity of maize silage, resulting in higher biogas yields than calculated based on the maize composition. (C) 2013 Elsevier Ltd. All rights reserved.