Enhanced nitrogen removal from secondary effluent of municipal wastewater using denitrification filter: Feasibility of refractory organics as a carbon source

[Display omitted] •Advanced nitrogen removal via PDA and denitrification was achieved in the DF.•Up to 89.9% and 67.5% of TN and COD were removed, respectively.•The hydrolytic products provided carbon source for PDA and denitrification process.•The demand for carbon sources was significantly minimized in the DF. Conventional advanced nitrogen removal in municipal wastewater is hindered by the limited availability of carbon sources in the secondary effluent. However, refractory organics present in it had the potential to serve as intrinsic carbon sources after hydrolysis for nitrogen removal via simultaneous denitrification and partial-denitrification anammox (PDA) processes. To assess this potential, a denitrification filter was set up in this study to evaluate its feasibility of concurrent processes. Results showed that increasing influent ammonium (NH4+-N) from 1.0 to 7.0 mg/L increased total nitrogen (TN) removal from 52.4 % to 89.9 %. Simultaneous occurrence of PDA and denitrification process were confirmed by the actual chemical oxygen demand (COD) consumption (0.8–1.2 mg/mg TN removal) from non-fluorescent organics. The presence of the anammox, hydrolytic and denitrifying bacteria further supported the achievement of nitrogen removal through PDA and denitrification processes by utilizing hydrolytic products biodegraded from refractory organics.