Biological Sulfide Oxidation in a Fluidized Bed Reactor

Abstract

Feasibility of a laboratory scale fluidized bed process for biological sulfide oxidation to elemental sulfur and the formation of well-settleable sulfur sludge is demonstrated. Sulfide oxidation strongly depends upon oxygen concentration, sulfide loading rate and upflow velocity. At reactor dissolved oxygen concentrations (DOr) higher than 0.1 mg l−1, sulfate was the main product of sulfide oxidation. Upon increasing the sulfide loading rate, the sulfate production rate decreased as sulfide oxidation to sulfur showed marked increase. Low formation of sulfate could mean that sulfide was inhibitory to sulfate producing bacteria or that conversion of sulfide to sulfur was more favorable than sulfate production. Sulfide conversions higher than 90% were obtained at sulfide loading rates of 0.13 - 1.6 kgS mr −3d−1. At DOr less than 0.1 mg l−1, sulfur was the major end product of the sulfide oxidation. Upflow velocity in the range of 16 - 26 m h−1 and sulfide loading rate of 0.9 - 1.6 kgS mr −3d−1 were necessary for generation of biogranules containing 65 - 76% of elemental sulfur. The elemental sulfur production of 76% was obtained at upflow velocity of 17 m h−1 with sulfide loading rate up to 1.6 kgS mr −3d−1. Morphological examination of the biogranules showed elemental sulfur deposition in the sludge granule and outside the bacterial cells.