Microbial aspects of autotrophic denitrification of wastewaters

Abstract

This chapter summarizes the investigations on the application of autotrophic denitrification in elemental sulfur packed bed reactors to nitrified leachate, secondary effluent, and flue gas desulfurization wastewater. Autotrophic denitrification using Thiobacillus denitrificans is an alternative to heterotrophic denitrification for wastewaters with a low BOD5/N ratio, as it can effectively remove nitrate from industrial wastewaters and secondary effluent. The fixed-film denitrification of nitrified landfill leachate is carried out using three identical packed bed reactors. The minimum retention time necessary for complete denitrification depends on sulfur particle size and influent nitrate concentration. The kinetic rate constants for autotrophic denitrification are lower than that for heterotrophic denitrification, because of slow sulfur dissolution rates. Thiobacillus denitrificans exhibit high salt tolerance, but are sensitive to temperature and pH. The microbial community consists mainly of Thiobacillus denitrificans according to microscopic observation. The attached growth of Thiobacillus denitrificans leads to the formation of microbially induced holes on the surface of the sulfur particles.