Institution: | Food and Bioprocess Engineering Group, Department of Food Science, Wageningen Agricultural University, PO Box 8129, 6700 EV Wageningen, The Netherlands Department of Environmental Technology, Wageningen Agricultural University, PO Box 8129, 6700 EV Wageningen, The Netherlands |
Abstract: | Solutions of sodium caprate and sodium laurate were digested in upflow anaerobic sludge bed (UASB) reactors inoculated with granular sludge and in expanded granular sludge bed (EGSB) reactors. UASB reactors are unsuitable if lipids contribute 50% or more to the COD of waste water: the gas production rate required to obtain sufficient mixing and contact cannot be achieved. At lipid loading rates exceeding 2–3 kg COD m−3 day−1, total sludge wash-out occurred. At lower loading rates the system was unreliable, due to unpredictable sludge flotation. EGSB reactors do fulfil the requirements of mixing and contact. They accommodate space loading rates up to 30 kg COD m−3 day−1 during digestion of caprate or laurate as sole substrate, at COD removal efficiencies of 83–91%, and can be operated at hydraulic residence times of 2 h without any problems. Augmentation of granular sludge in lab-scale EGSB reactors was demonstrated. The new granules had excellent settling properties. Floating layer formation, as well as mixing characteristics in full-scale EGSB reactors require further research. |