Anaerobic digestion of wheat grass under mesophilic and thermophilic conditions and different inoculum sources

Anaerobic digestion of lignocellulosic biomass can be used to produce in one single step different products with applications as fuels or as bulk chemicals such as methane, ethanol and other particular volatile fatty acids: acetic, propionic and butyric acids. This study aims to investigate the anaerobic digestion of
lignocellulosic biomass (wheatgrass) in batch condition under mesophilic (40°C) and thermophilic (50°C) conditions, two inoculum concentrations and different microbial sources: anaerobic digester sludge and soil. Vials of wheatgrass powder (20 g/l) were inoculated and maintained under anaerobic condition in a water bath shaker with temperature control. The results showed that both inocula were able to hydrolyse lignocellulose biomass without physicochemical pre-treatment, but higher VSS and TC removals were achieved when anaerobic sludge inoculum was used. Acetic acid was the main product for the different batch conditions and corresponded to around 60% of the CODproducts. Butyric acid, propionic acid and ethanol were identified in lower concentration. The maximum volatile suspended solids (VSS) and total carbohydrates (TC) removal
were (44 ± 5) % and (50 ± 11) % respectively. The maximum yield of products in the liquid phase was 37% in COD basis.