Retention of sulfate-reducing bacteria in expanded granular-sludge-blanketreactors

In acetate-fed, expanded granular-sludge-blanket reactors with a liquid upf low 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 demineral ized tap water promoted methane production. In a formate-fed, sulfate-reduc ing, 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 upf low velocity tested (3.0 m/h). The latter was only possible if methane-prod ucing bacteria were repressed by two consecutive doses of 3.85 gn 2-bromoet hane sulfonate. These laboratory-scale experiments confirm the presumed lim ited capacity of sulfate-reducing bacteria to multiply to high biomass dens ities in upflow reactor systems.