Reduction of produced elementary sulfur in denitrifying sulfide removal process.

Denitrifying sulfide removal (DSR) processes simultaneously convert sulfide, nitrate, and chemical oxygen demand from industrial wastewater into elemental sulfur, dinitrogen gas, and carbon dioxide, respectively. The failure of a DSR process is signaled by high concentrations of sulfide in reactor effluent. Conventionally, DSR reactor failure is blamed for overcompetition for heterotroph to autotroph communities. This study indicates that the elementary sulfur produced by oxidizing sulfide that is a recoverable resource from sulfide-laden wastewaters can be reduced back to sulfide by sulfur-reducing Methanobacterium sp. The Methanobacterium sp. was stimulated with excess organic carbon (acetate) when nitrite was completely consumed by heterotrophic denitrifiers. Adjusting hydraulic retention time of a DSR reactor when nitrite is completely consumed provides an additional control variable for maximizing DSR performance.