The influence of organic load on granular sludge development in an acetate-fed system

The development of granular sludge in laboratory upflow anaerobic sludge blanket reactors was examined. The carbon source was acetate to select the acetotrophs Methanosarcina and Melanothrix. Their ratio was monitored using the differences in their F420-coenzyme contents. The acetate levels in the feed were 0.5-3.0 g per litre. The hydraulic retention time was 10.9 h. Granulation occurred faster in the reactors with the higher acetate concentrations. The granules were less firm and dense than those grown on a starch substrate. A decrease in specific F420 activity, an increase in Methanothrix and the appearance of a clear interface between the sludge blanket and the sludge bed occurred at nearly the same time.