Modified integrated fixed-film activated sludge process: Advanced nitrogen removal for low-C/N domestic wastewater.

Actual low-C/N domestic wastewater was treated using the high-concentration powder carrier bio-fluidized bed (HPB) process comparing diatomite and Fe-C as the carriers. The total nitrogen removal efficiencies were increased from 50.08% to 65.40% and 78.58%, respectively. The diatomite HPB process increased the relative abundance of autotrophic N-cycle bacteria to more than twofold and the sludge size. Therefore, the contributions for nitrogen removal by anammox and simultaneous nitrification-denitrification were increased. The Fe-C HPB process improved the nitrogen removal efficiency mainly by increasing the biodegradability and activities of electron transfer system and key enzymes. The key device (hydrocyclone separator) of the HPB process significantly improved the recovery efficiency of the carriers. It also improved the capacity of microbial aggregations for adsorbing pollutants. Furthermore, it reduced the relative abundance of filamentous bacteria. This study demonstrated the feasibility and mechanism of the HPB process for improving the nitrogen removal efficiency for low-C/N wastewater.