Use of elemental sulfur and thiosulfate as electron sources for water denitrification

This study aims at comparing the sulfur-based autotrophic and mixotrophic denitrification performances in fixed-bed bioreactors to reveal the impact of alkalinity source, methanol supplementation and use of thiosulfate as electron source. Three different columns were operated. Reactor 1 was packed with elemental sulfur (3-5 mm) and limestone (1-3 mm). The second reactor (reactor 2) was packed with elemental sulfur (3-5 mm) and bicarbonate was used as alkalinity source. In the third reactor (reactor 3), thiosulfate and bicarbonate were used as electron and alkalinity sources, respectively. Nearly complete autotrophic denitrification was attained at loading rates of 0.1, 0.36, and 0.1 g NO3 (-)-N/(L day) in reactors 1, 2 and 3, respectively. Sulfate generated in autotrophic denitrification processes was nearly stoichiometric. Stimulating simultaneous heterotrophic and autotrophic denitrification by dozing methanol increased denitrification rate up to 0.72 g NO3 (-)-N/(L day), decreased alkalinity requirement, and reduced sulfate generation.