Remediate black-odorous sediment by slow-release calcium nitrate: Migration, transformation and microbial succession

Calcium nitrate has been widely used in-situ remediation of black-odorous sediment, which microorganisms mainly utilized nitrate to redox substances through denitrification. However, this technique has the problem that the local nitrate concentration was too high to inhibit the activity of functional microorganisms, which affected the oxidation effect and caused the abnormal release of inorganic nitrogen from the sediment. The slow release of calcium nitrate by tube dosing can effectively solve this disadvantage. However, the specific layout of the dosing method needs further research. Therefore, a method of tube-dosing distribution points was proposed by explored the migration and transformation laws of N-S-Fe in the vertical and horizontal directions of the sediment and the changes in the microbial community structure after the fixed-point dosing of calcium nitrate in this study, which further optimized the calcium nitrate dosing process and provided a new dosing method and idea in practical application. Within one month, nitrate migrated and transformed vertically and horizontally, accompanied by the accumulation of nitrite, oxidation of acid volatile sulfide (AVS) and ferrous iron. Among them, within the nitrate migration distance of 0-6 cm (vertical) and 0-8 cm (horizontal), the removal rate of AVS reached 100% and ferrous iron was effectively oxidized. In addition, in the process of vertical and horizontal migration, bacteria closely related to sulfide and ferrous iron-driven denitrification, such as Thiobacillus, Sulfurimonas and Thio-alkalispira, were found to be dominant. These results demonstrate that after exploring the vertical and horizontal migration and transformation laws of nitrate in different contaminated sediments remediated, the reasonable layout of dosing methods can be carried out in practical application.