Efficient biological nitrogen removal by Johannesburg-Sulfur autotrophic denitrification from low COD/TN ratio municipal wastewater at low temperature

A novel system integrating Johannesburg (JHB) and sulfur autotrophic denitrification (SAD) process was proposed to enhance nitrogen removal in treating low COD/TN ratio (COD 129 mg/L, TN 29mg/L on average) municipal wastewater at low temperature (12.2 +/- 0.5 degrees C). The results showed that under an HRT of 11.3 h, the JHB process effluent COD, TN, and NH4+-N were 32, 13.8, and 1.6 mg/L on average, respectively. Since NO3--N was the prominent compound of TN (average 80.6 %) and COD was low in JHB effluent, the SAD process utilized sulfur granule as electron donor for autotrophic denitrification was employed to remove the rest NO3--N of the JHB process. In JHB-SAD system, heterotrophic denitrification cooperated with autotrophic denitrification to enhance nitrogen removal. It was found that 87.0 % JHB effluent nitrogen was removed by SAD process under the most efficient nominal hydraulic retention time (HRT) of 0.32 h. The SAD process effluent of COD, TN, and NH4+-N were 21, 1.8, and 1.0 mg/L, respectively. Most importantly, the JHB-SAD system could achieve complete nitrogen removal theoretically as long as the NH4+-N was sufficiently oxidized. The nitrogen removal performance of JHB-SAD system is attractive in treating low COD/TN ratio municipal wastewater at low temperature. Moreover, SAD process was well adapted for limited space because of the efficient NO3--N removal, which was propitious to upgrade wastewater treatment plant.