Assessing Elemental Sulfur Based Denitrification as a Biofilm Process<strong></strong>

<p>Elemental sulfur (S^o) can serve as an electron donor for denitrification of water and wastewater, and there is an increasing interest in its use in biological treatment processes. However, S^o-based denitrification is not well characterized, and most past research has neglected its behavior as a biofilm process. In this study, the kinetic behavior of S^o-based denitrifcation was assessed, kinetic and stoichiometric parameters for S^o-based denitrification intermediate steps were determined, and the use of S^o for denitrifying filters was investigated. </p><p>S^o packed-bed reactors were used in kinetic behavior study for S^o-based denitrification biofilm process. Results suggest that S^o-based denitrification can achieve fluxes comparable to heterotrophic processes if the biofilm develops sufficiently, but fluxes may decrease with excessive biofilm development. It was found that biofilm development affects the relationship between denitrification fluxes and bulk nitrogen species (NO₃^-, NO₂^-) concentrations. NO₂^- accumulation was found related to electron limitation and different affinity of nitrogen species. </p><p>Batch studies were used in order to estimate kinetic parameters for denitrification intermediate steps. This study found that the maximum specific rate of reduction, , for N₂O was larger than for NO₃^- and NO₂^-. The for NO₂^- was lower than that for NO₃^-, providing a potential explanation for why NO₂^- tends to accumulate in S^o-based denitrification. </p><p>S^o packed denitrification filters were used to investigate the feasibility of using S^o in a plug flow system. Results suggest that S^o granular denitrifying filter was a more promising option, where backwashing did not have detrimental effects on the denitrification performance. Supply of secondary effluent could improve the recovery of NO₃^- removal after backwashing. Extended periods of NO₂^- accumulation were not observed when secondary effluent was supplied.</p>