Comparison of UASB and fluidized-bed reactors for sulfate reduction

Abstract

Reactor hydrodynamics is important for sulfidogenesis because sulfate reduction bacteria (SRB) do not granulate easily. In this work, the sulfate reduction performance of two continuous anaerobic bioreactors was investigated: (i) an upflow anaerobic sludge blanket (UASB) reactor and (ii) a fluidized bed reactor (FBR). Organic loading, sulfate reduction, and COD removal were the main parameters monitored during lactate and glycerol degradation. The UASB reactor with biomass recirculation showed a specific sulfate reduction rate of 0.089±0.014 g.gSSV -1.d -1 (89% reduction), whereas values twice as high were achieved in the FBR treating either lactate (0.200±0.017 g.gSSV -1.d -1) or glycerol (0.178±0.010 g.gSSV -1.d -1). Sulfate reduction with pure glycerol produced a smaller residual COD (1700 mg.L -1) than that produced with lactate (2500 mg.L -1) at the same COD.sulfate -1 mass ratio. It was estimated that 50% of glycerol degradation was due to sulfate reduction and 50% to fermentation, which was supported by the presence of butyrate in the FBR effluent. The UASB reactor was unable to produce effluents with sulfate concentrations below 250 mg.L -1 due to poor mixing conditions, whereas the FBR consistently ensured residual sulfate concentrations below such a value.