Potential of sulfide-based denitrification for municipal wastewater treatment

Wastewater treatment through anaerobic carbon removal followed by sulfide-based denitrification for nitrogen removal offers significant advantages over conventional processes in terms of decreased sludge production and reduced energy requirements. While the process has been demonstrated to treat wastewater with very high sulfate concentrations resulting from saline water supply, this contribution assesses the potential of sulfide-based denitrification for a broader range of municipal wastewater characteristics. A mass balance-based calculation procedure was presented to determine the optimal recycle ratio and the corresponding effluent nitrogen concentrations in a pre-denitrification system. The calculation procedure was first validated with experimental data from literature and was then applied to various scenarios. The latter showed that legal effluent requirements may be achievable only for specific municipal wastewater streams with a low nitrogen concentration and an elevated sulfate content (>42 g S m(-3)), e.g. close to the sea, or if a significant amount of biodegradable carbon enters the anoxic reactor to stimulate auxiliary heterotrophic denitrification. A stoichiometric calculation illustrated that even with external carbon addition to supplement the sulfide-based denitrification, the total sludge production and aeration energy could still be reduced compared to a scenario with purely heterotrophic denitrification. Finally, it was shown that a broader range of wastewater types could be treated when applying nitrification-denitrification over nitrite instead of over nitrate, due to the lower sulfide and carbon requirements for the reduction of nitrite