The Adaptation of Anaerobic Granulated Bed to Changes in Loading Rate and Liquid Upflow Velocity in UASB Reactors

Abstract

Abstract Four 20L UASB reactors, R1, R2, R3 and R4 were operated at different upflow velocities of 0.25, 1.0, 1.5, and 0.5 m/h, respectively. Changes in loading rate were achieved by removing part of granules from the bed at a constant volumetric feed rate of 6.2 g COD/(L day). It was found that the granulated bed may adapt to the increased organic loading rate up to about 1.6 kg COD/(kg VSS day) and achieve a 100% conversion of the COD present (composed of volatile fatty acids). Increasing the loading rate over the above value can bring about a decreased COD conversion. At the organic loading rate of 1.6 kg COD/(kg VSS day), the accumulation of granules in reactors R1 and R4 was observed. At the same loading rate, no accumulation of granules was observed in reactor R2 (within 40 days) and in reactor R3 (within 55 days). It was also found that a great number of large granules were washed out from reactors R1 and R4 when the loading rate of about 0.7 kg COD/(kg VSS day) was maintained for about 70 days.