Dynamic characteristics of immobilized microorganisms for remediation of nitrogen-contaminated groundwater and high-throughput sequencing analysis of the microbial community

Abstract The aim of this study was to investigate the effect of adsorption by a composite active medium (nitrogen-degrading bacteria immobilized on scoria) on the removal of ammonium nitrogen (NH4+-N), nitrite nitrogen (NO2–N) and nitrate nitrogen (NO3–N). Transport of these three forms of nitrogen was investigated using columns with different flow rates, initial concentrations and depths. Immobilization of the bacteria on the scoria significantly enhanced the ability of the composite active medium to remove nitrogen during the remediation process. As the flow rate increased, the shear force increased and solute diffusion decreased, thereby improving the tolerance of the bacteria for the three forms of nitrogen and reducing the penetration time. Increasing the initial nitrogen concentration resulted in a decrease in the adsorption rate constant (KTh). The nitrogen-degrading bacteria immobilized on scoria rapidly reached saturation with regards to their nitrogen adsorption capacity. The initial nitrogen concentration of each media layer was different, and the composite active medium had a certain blocking effect, which resulted in a slow increase in the concentration of nitrogen in the deeper media layer. The transport experiments showed that the process accords with the thomas model and the Bohart-Adams model. The contents of the three forms of nitrogen were within acceptable standards for drinking water after 2 months of a column containing the composite active medium. The composite active medium can be used for in situ and ex situ remediation of groundwater containing excessive nitrogen. High-throughput sequencing analysis was used to monitor the composition of the bacterial community present within the composite active medium. During the remediation process, there were only slight changes in the structure and composition of the nitrogen-degrading bacterial community, although there were clear differences in abundance. Pseudomonas, Stenotrophomonas and Serratia were the three bacterial genera that were effective removal of all three forms of nitrogen.