Retention of Sulfate‐Reducing Bacteria in Expanded Granular‐Sludge‐Blanket Reactors

Abstract

In acetate‐fed, expanded granular‐sludge‐blanket reactors with a liquid upflow velocity between 3.5 and 4.5 m/h and pH 8.0 to 8.5, calcium‐containing tap water tended to select for sulfate‐reducing bacteria, whereas demineralized tap water promoted methane production. In a formate‐fed, sulfate‐reducing, expanded granular‐sludge‐blanket reactor operated at pH 8.25 to 8.65, maximum sulfate removal rate was 9.5 g sulfur/L·d at the slowest liquid upflow velocity tested (3.0 m/h). The latter was only possible if methane‐producing bacteria were repressed by two consecutive doses of 3.85 g/L 2‐bromo‐ethane sulfonate. These laboratory‐scale experiments confirm the presumed limited capacity of sulfate‐reducing bacteria to multiply to high biomass densities in upflow reactor systems.