Immobilized denitrifying bacteria on modified oyster shell as biofilter carriers enhance nitrogen removal

Biocarriers play a vital role in water treatment in recirculating aquaculture systems. In this study, modified oyster shell (OS)-immobilizing denitrifying bacteria were applied as biocarriers in biofilters. The results revealed that CaCO3 was the main component of the OS calcined at 200 degrees C (OS200), 400 degrees C (OS400), and 600 degrees C (OS600). The surface area and microbe-immobilizing ability of OS200, OS400, and OS600 were enhanced. After immobilizing Pseudomonas putida DS2 and Pseudomonas chengduensis BF6, the average total nitrogen (TN) removal efficiencies of OS400-P (Pseudomonas sp. DS2 and BF6 immobilized onto OS400) and OS600-P (Pseudomonas sp. DS2 and BF6 immobilized onto OS600) reached 50.25% and 61.50%, respectively. The microbial and functional gene richness in the biofilters filled with biocarriers made of OS-immobilizing denitrifying bacteria changed. The genus Pseudomonas became the dominant microbe, which was positively correlated with NO3- -N + NO2- -N (p < 0.001), and TN removal (p < 0.01). Overall, these findings indicate that applying OS immobilizing denitrifying bacteria as biocarriers can be a novel strategy to enhance nitrogen removal in biofilters.