Effect of ferrous iron on the settling properties of granular sludge in a UASB reactor

The effect of ferrous ion addition on the settling properties of the granules in an upflow anaerobic sludge blanket (UASB) reactor was investigated. A UASB reactor (35oC; pH=7) was operated for 3 months at a 20-h hydraulic retention time (HRT) at organic load from 2,0 to 20,0 gCOD . L -1. d -1 . Ferrous iron as FeSO4 . 7H2O was fed to the reactor in a range of load from 0,03 to 0,28 g Fe +2. L -1. d -1 . After steady state conditions were achieved, the settling properties of granular sludge from the anaerobic sludge bed reactor were determined by using a novel upflow velocity test. From the results, it was concluded that iron promoted granulation. The U10% (10% of sludge washed out by applying upflow velocity U10%) was increased from 0,23 m.h -1 to 13,21 m.h -1 , while U30% from 0,87 m.h -1