Application of positively charged red mud-based carriers for anaerobic ammonium oxidizing bacteria biofilm formation

Enrichment of anaerobic ammonium oxidizing bacteria (AnAOB) in the anaerobic ammonium oxidation (anammox) process remains a challenge in engineering applications. In this study, for faster enrichment of AnAOB, red mud-based carriers were positively charged with FeCl3 and microbial promoters. The experimental results showed that the average nitrogen removal rates of the red mud-based carriers (RMGA), FeCl3-modified red mud-based carriers (RMGA-Fe), and microbial promoter-modified red mud-based carriers (RMGA-MA) increased by 24.4%-175% compared with the commercially available K3 carriers. Combining the results of SEM and laser confocal microscope, electrostatic attraction played a leading role on loading AnAOB. The increase in the surface roughness and specific area of the carriers after the attachment and the presence of Fe2+, Ca2+, and Mg2+ plasma were necessary for the subsequent growth of AnAOB, while the leaching of Cr(VI) promoted the nitrogen removal effect of AnAOB.

Automated summary

This study aimed to enrich anaerobic ammonium oxidizing bacteria (AnAOB) in the anaerobic ammonium oxidation (anammox) process. Red mud-based carriers were positively charged with FeCl3 and microbial promoters for faster AnAOB enrichment. The experimental results showed significantly increased nitrogen removal rates compared to commercially available carriers. Electrostatic attraction played a leading role in loading AnAOB, and an increase in surface roughness and specific area of the carriers, as well as the presence of certain ions, were necessary for AnAOB growth. The leaching of Cr(VI) promoted the nitrogen removal effect of AnAOB.