Comparison of reactive porous media for sulfur-oxidizing denitrification of high nitrate strength wastewater

Three packing materials for sulfur oxidizing denitrification packed bed systems seeded with acclimated anoxic sludge were evaluated. Two porous media were prepared via thermal fusion with sodium bicarbonate as porogen: sulfur fused with powdered (1) calcium carbonate (CaCO3) (SCa) and (2) oyster shell (SCr). Randomly packed sulfur and limestone granules (S + L) media were used as the control. Results revealed that SCr is the most suitable media as it exhibited the highest nitrate removals and lowest nitrite accumulation. It has macrovoidal pores which facilitated microbial attachment. Additionally, SCr had the highest CaCO3 loading per unit volume and highest media dissolution rate which was favorable to avert pH decrease. But due to high denitrification activity, high sulfate levels in SCr may necessitate a post-treatment step prior to effluent discharge. Due to poor biomass attachment, S + L is most sensitive to change in fluid flow condition. As hydraulic retention time is decreased, S + L exhibited intensive and irreversible performance decline. Inferior denitrification performance of SCa was mainly due to low CaCO3 loading per unit volume, low dissolution kinetics and low alkalinity consumption by denitrifiers. Using modified Stover–Kincannon kinetic model, overall performance and denitrification capacities can be arranged as SCr > S + L > SCa.

► Porous sulfur-oxidizing denitrification media were synthesized via thermal fusion.
► Synthesized media provided sulfur and alkalinity sources.
► Media properties influenced denitrification performances.
► Macrovoidal media structure promoted biomass attachment and substrate supply.
► Porous sulfur/crushed oyster shell was the most effective media for denitrification.