Enhancement of biogas production from agricultural wastes via pre-treatment with advanced oxidation processes

The effects of advanced oxidation processes (AOPs) including Fenton, ozone, and ozone combined with Fe(II) and H2O2 on disintegration/solubilization of three mixed agricultural solid wastes and subsequent anaerobic digestion were studied. Hydroxyl radicals (center dot)(OH) generated from AOPs enhanced the oxidation of COD and solubilization of particulate COD (>0.45 mu m). Upon treatment, substrates lost 15.2 to 29.5% of their solids, 33.6 to 37.5% of total chemical oxygen demand, 16.5 to 25% of total biopolymers (humic acids and protein). The soluble matter content increased by 3-6 folds facilitating metabolization rate of the treated substrate resulting in a 23-30% increase in the cumulative methane production and 11.2-25% increase in % digestion efficiency (%eta(AD)). Semi-batch tests revealed that mixing fresh and pre-treated substrate using a 50:50 ratio improved both the specific methane production (1.7 folds) and volatile sold reduction (79%) with a positive effect on sludge dewaterability.