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Upflow anaerobic sludge blanket (UASB) process is now widely used for the treatment of industrial wastes. Immobilized methanogenic granules play a vital role in such a process. In this study, microbial diversity of these granules from five different full-scale and laboratory UASB reactors operating under different conditions was investigated. The results were categorized on the basis of four different cases of operational and environmental conditions. Predominant methanogens in granules operating under a specific set of operational or environmental conditions were generally different from each other. The results indicated that microorganisms resembling those of the genera Methanobacterium, Methunobrevibacter, Methunothrix and Methunosarcina dominated the granules. However, a variety of other species co-existed with the dominant methanogens. The presence of diverse bacterial groups manifested a unique property of the granules of seeding and fast start-up of other UASB reactors.

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A laboratory upflow anaerobic sludge blanket reactor, seeded with fine, suspended, bacterial floc with 1.76 g volatile suspended solids/l, was used to treat synthetic methanolic waste. After 180 days of continuous peration, granular sludge with discrete granules of 1 to 2 mm diam. was formed, with 52 g volatile suspended solids/l. Granules were brown, relatively soft and had a settling velocity of 1.61 cm/s. Extracellular polymeric matter extracted from the granular sludge had high carbohydrate content but low nucleic acid content. The ash of the granular sludge contained Na(+), K(+) and Mg(2+) up to 15.0, 11.7 and 3.75 mg/g, respectively. Scanning and transmission electron microscopy revealed that the granular sludge was dominated by methanogens resembling Methanosarcina.