Elemental Sulfur (So) as a Supplemental Electron Donor for Wastewater Denitrification: Batch and Column 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 the kinetics and stoichiometry of So based denitrification. Using a series of batch reactors with 20 and 30 mgN/L nitrate, nitrite was found to accumulate during denitrification, and nitrite removal appeared to be slowed or completely inhibited. The stoichiometry for nitrate conversion to nitrite was estimated from these batch tests. The fs (fraction of electrons to biomass synthesis) was 0.54±0.03, and the biomass yield was 0.41±0.03 gVSS/gSo for batch reactors using So chips. For reactors with So powder, the results were similar: fs was 0.58±0.03 and the yield was 0.44±0.02gVSS/gSo. Two So packed-bed reactors, which had been running for 200 days, were used to determine the effects of backwashing and bioaugmentation with biofilm removed from the reactor. Vigorous backwashing removed all visible biomass. Reactors needed 2-4 days to remove nitrate and 11-13 days to remove nitrite. Adding biomass after backwashing improved the initial nitrate removal rate and the acclimation time, but had little effect on nitrite removal.