Properties of anaerobic granular sludge as affected by yeast extract, cobalt and iron supplements

Abstract

The effect of yeast extract (YE), iron (Fe) and cobalt (Co) on anaerobic bacterial granules grown in eight laboratory-scale upflow anaerobic sludge blanket reactors was investigated using a factorial design. The experiment was performed in three periods in which different chemical oxygen demand (COD) loading rates were applied to the reactors. The COD digestion rate and the specific activity of the bacteria were positively affected by supplementation of Fe and Co in the feed under a high COD loading rate. YE had a strong positive effect on the bacterial growth rate, but no significant effect on the specific activity of the bacteria. With Fe supplementation, an excellent COD digestion rate was maintained in the reactors, and addition of YE in the feed was not necessary. Granules with better settling properties were developed under a relatively low bacterial growth rate. With the increase in COD loading rate, the percentage of calcium increased rapidly in the granules from the reactors without YE supplementation. The bacteria grown under high COD loading rate and without an Fe supplement could be Fe-deficient. Methanothrix-like rod-shaped bacteria were dominant in the granules from all reactors.