Mechanism of aerobic denitrifiers and calcium nitrate on urban river sediment remediation

Calcium nitrate, coupled with aerobic denitrifiers, were applied to reduce nitrogen and organic pollutants of urban river sediment. 115-day remediation tests showed that total nitrogen in the sediment decreased by 16.5%, while total transferable nitrogen increased from 0.097 to 0.109 mg/g. Increased urease activity and decreased protease showed a potential for further nitrogen degradation. Although the total organic carbon (TOC) content decreased slightly, the predominant organic pollutants were removed or converted to low molecular weight compounds through microbial biodegradation. Decreased phenol oxidase activity exhibited that low concentrations of recalcitrant aromatic compounds remained in the sediment. The high-throughput sequencing results reveals that the community diversity of bacteria markedly increased. Compared with the addition of calcium nitrate or aerobic denitrifiers alone, genera mainly removed nitrogen and organic compounds, especially recalcitrant compounds, following the treatment with the combination technology. Moreover, the concentrations of nitrogen and organic matter did not increase significantly in the overlying water, which was free of undesirable secondary pollution. During the process of remediation, dosing with nitrate may provide a more favorable environment for aerobic denitrifiers and indigenous microbes in the sediment. Furthermore, the introduced aerobic denitrifiers may improve nitrogen removal and have a collaborative effect with indigenous microbes.