UASB treatment of liquid residues from grass bioraffination

In 2001 the first green biorefinery started operation in Switzerland with a design load of 5,000 tons dm of grass per year and a combined output of fibres (0.4 tons per ton input), protein (160 t/t) and bioenergy (500 kWh/t). Bioenergy was produced in a 570 m³ UASB reactor which has been monitored intensively during its first year of operation. Anaerobic treatment of liquid residues with >80% degradation of organics was shown up to high f/m ratios and loading rates of 12–15 kg COD/m³ d and specific biogas production of 0.5–0.65 Nm³ of gas per kg of COD added. A mass flow analysis of solids and pellets leads to the conclusion, that due to a low sludge bed volume of only 16% of the reactor combined with a low actual organic loading of 1.5 kg COD/m³ d there was a restricted adsorption and a low degradation of substrate solids.