Nitrogen removal via simultaneous partial nitrification, anammox and denitrification (SNAD) process under high DO condition.

The simultaneous partial nitrification, anammox and denitrification (SNAD) process for treating domestic wastewater was investigated in a sequencing batch reactor (SBR). The SBR was operated with air flow rate of 500 L h at 30 °C. Domestic wastewater was used as influent and Kaldnes rings were used as biomass carriers. In the beginning, long aeration condition was implemented to cultivate nitrification biofilm. Afterwards, intermittent aerobic condition was conducted during the cycle operation. The influent organic matter loading rate was improved by reducing the aeration and mixing times. Consequently, when the SNAD biofilm reactor was fed with the organic matter loading rate of 0.77 (kg COD m d), the bio-bubbles appeared in the reactor and the total inorganic nitrogen (TIN) removal efficiency decreased. After the organic matter loading rate decreased to 0.67 (kg COD m d), the reactor showed excellent nitrogen removal performance. The TIN removal efficiency varied between 80 and 90 %, and the average TIN removal loading rate was 0.22 (kg TIN m d). Additionally, the scanning electron microscope (SEM) observation confirmed that the anammox bacteria located in the inner part of the carriers. Finally, the microbial community analysis of 16S rRNA gene cloning revealed that the anammox bacteria on the carriers consisted of three main genuses: Candidatus Brocadia sp., Candidatus Brocadia caroliniensis and Candidatus Brocadia fulgida.