The use of sulfur and sulfide in packed bed reactors for autotrophic denitrification

In recent years there has developed con siderable interest in the removal of nitrates from waste streams. One of the most eco nomical and effective means of nitrate re moval is biological denitrification. In water and wastewater treatment studies denitrifica tion is usually a heterotrophic process in which methanol is generally considered the most effective organic carbon supplement. However, the rising cost of organic com pounds makes methanol, and similar organic compounds, undesirable as chemical additives. It would be advantageous to develop an autotrophic denitrification system and thereby eliminate process dependence on organic sup plements. ThiobaciUus denitrificans is a motile, fac ultative, gram-negative, non-spore forming, autotrophic bacteria. It oxidizes sulfur and sulfur compounds while reducing nitrate to free nitrogen. This organism may be used as part of a water or wastewater treatment process to remove nitrates if an exogenous sulfur source and an anaerobic environment are provided. Several investigators have demonstrated the ability of T. denitrificans to denitrify.1' 2 Sikora and Keeney3 demonstrated the ability of T. denitrificans to denitrify a nitrified septic tank effluent in a packed bed sulfur reactor. Batchelor4 used powdered sulfur as an elec tron donor in complete mix slurry-type re actors to obtain good nitrate removals. Bisogni and Driscoll7 used thiosulfate as an electron source for denitrification in semi-continuous