Sulfate reduction during the acidification of sucrose at pH 5 under thermophilic (55 degrees C) conditions. II: Effect of sulfide and COD/SO42- ratio

This work studied the effect of the sulfide concentration and COD/SO42- ratios (4 and 1) on sulfate reduction and acidification in a thermophilic (55 degrees C) UASB reactor fed with sucrose (4 g COD (I-reactor d)(-1)) operated at a reactor mixed liquor pH controlled at 5 for a period of 301 days. When implementing N-2 stripping, sulfate reduction efficiencies up to 95%, corresponding to volumetric sulfate reduction rates of 0.87 and 4.2 g (I-reactor d)(-1) at the COD/SO42- ratios of 4 and 1, respectively, were achieved. Sulfide was toxic to sulfate reduction at a total dissolved sulfide concentration of 100 mg l(-1). Acidification was always complete and acetate was the only form of substrate in the effluent at a COD/SO42- ratio of 1. The sludge was well retained in the reactor and kept its granular shape throughout the reactor run.