A two-phase UASB system was operated for high-rate treatment of concentrated distillery wastewater. The phase separation was obtained by adjusting pH in each reactor. When influent SS concentration was 4.1 g/l, the first phase UASB reactor was effectively operated up to the loading rate of 16.5 kg COD/m3.day, producing 3.9 g HAc/l.day. In the methanogenic UASB reactor, loading rates up to 44 kg COD/m3.day could be applied while removing 80 % of influent COD with a specific gas production of 16.5 l/l.day. After the formation of granular sludge in both reactors, it was possible to maintain the appropriate pH in the first phase only by recirculating the effluent from the methanogenic phase without the addition of alkaline chemicals. The morphological study on the granular sludge consortia was made with both scanning and transmission electron microscopes. It was interesting to find the granules of different color and shape in the acidogenic phase in 90 days and in the methanogenic phase in 120 days after start-up. The acidogenic granular sludge mainly consisted of long chains of large rods, short plump rods, and various size of cocci, which have a different shape and cytoplasmic appearance from common methanogenic bacteria. Whereas the long multicellular filaments of Methanothrix spp. were prevalent in the methanogenic granule, diverse bacteria were entrapped therein.

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