Elemental Sulfur (S°) as a Supplemental Electron Donor for Wastewater Denitrification

Many utilities are seeking more cost effective, safe, and reliable electron donors for biological nutrient removal (BNR). Elemental sulfur (S°) may be an attractive option, but little is known about the feasibility of S°-based denitrification and its kinetics. In this research, we used bench–scale, S° packed–bed reactors to determine denitrification fluxes as a function of bulk concentrations. Both nitrate and nitrite were removed after 30–50 days. Maximum fluxes were 0.8 gN/m2-day to 1 gN/m2-day. As biofilm thickness increased over time, maximum fluxes increased. However, fluxes for low nitrate condition decreased, providing an increase in the apparent Ks for nitrate. Reactors maintained sustained high fluxes for over 140 days, without any backwashing. However, when a vigorous backwashing was carried out, all the biomass was lost and the reactor needed a 30-day period to return to previous fluxes. Results suggest that biomass production is slow, as expected for an autotrophic system, but that reasonably high denitrification fluxes can be obtained. Care must be taken not to remove excessive biomass during backwashing.