Changes in pre-formed granule composition and structure in a sulphidogenic uasb treating a synthetic ferric oxalate wastewater

The effect of treatment of an acidic, high sulphate/iron bearing, oxalate wastewater on pre-formed granule composition and structure in an upflow anaerobic sludge blanket (UASB) reactor was studied. The results indicated that this wastewater did not lead to the formation of new granules in a pre-seeded reactor. Ferrous precipitates which accumulated at the base of the reactor acted as a surface for adsorption of bacterial cells, and a majority of the substrate degradation occurred in this lower region. The presence of Desulfosarcina on the precipitate surface confirmed the sulphidogenic nature of the system, and these organisms outcompeted the methanogens present. After 18 months of operation compressed ellipsoidal granules were identified in the upper layers of the sludge bed, and these were proposed to be the original inoculum granules following displacement from the reactor bed and compression caused by precipitate build up.