Moving-bed biofilm reactor for saline wastewater treatment: Different types of carriers, versatile nitrifying reactions, and functional microbial groups

Abstract

The biofilm carriers are of significance for the operation of the moving bed biofilm reactor (MBBR) system. However, knowledge about the nitrification process with different types of carriers is still limited, particularly for saline wastewater treatment. In this study, six different carriers were applied to assess their ability for nitrification in the MBBRs through a long-term continuous operation with the hydraulic retention time reduced from 21.6 h to 3.1 h. Ammonia removal could be effectively achieved with a loading rate up to 14 g NH4+-N/d in all carriers (>91 %), except for carriers 3 (84 %) and 4 (78 %). Moreover, partial nitrification was established and maintained in the MBBR with carrier 4, while full nitrification occurred in others. The microbial structure revealed that, ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and denitrifiers were dominant with the overall relative abundance of 38.82 %, 51.30 %, 26.90 %, 59.84 %, 49.54 %, and 51.92 % in each MBBR, suggesting the possibility of achieving simultaneous nitrification and denitrification. The findings of this study have shed lights into the nitrogen conversion in MBBRs with different carriers for saline wastewater treatment.