Elemental Sulfur (So) as a Supplemental Electron Donor for Wastewater Denitrification: Denitrification Filter Studies

Many utilities are seeking more cost-effective, safe, and reliable electron donors for biological nutrient removal (BNR). Elemental sulfur (So) may be an attractive option, but little is known about the feasibility of So based denitrification and its kinetics. This study furthered our investigations into using So powder for BNR applications, specifically its use in denitrifying filters. The relationship between fluxes and nitrate (NO3−) concentrations obtained from the granular sulfur packed-bed reactor was used to estimate required So amount. Using either So powder or methanol as electron donors, two laboratory-scale denitrification filters fed with tap water were investigated. Denitrification did not take place until around day 50 for both filters. NO3− was removed from around 8mgN/L to 4mgN/L in the So powder-based denitrification filter, with around 1 mgN/L of nitrite (NO2−) accumulation. However, due to the increasing headloss and salt precipitation, water overflowed and resulted in discontinuous feeding of media. The So powder-based filter appears to recover slowly after an upset, compared to methanol-based filter. Complete denitrification was not achieved as expected. Accumulated headloss at different depths of the filters for both filters were monitored, suggesting bumping and backwashing are needed.