Synergistic effect of Ca(NO3)2 - CaO2 on the improvement of sediment microecology: Transformation of sulfur and ferrous iron, and improvement mechanism

Abstract

The synergy of Ca(NO3)2 and CaO2 can effectively reduce the risks of secondary pollution caused by nitrate escape and release. However, the timing and suitable dosage of Ca(NO3)2 and CaO2 during the synergistic interaction have not been fully investigated. In this work, we separated acid volatile sulfides (AVS) oxidation and ferrous iron oxidation by controlling the dosage of Ca(NO3)2. Results indicated that at a low RN/1.6S2−ratio, there was an obvious competitive relationship between AVS oxidation and ferrous iron oxidation, and sulfide was oxidized prior to ferrous iron. More efficient AVS and ferrous iron oxidation was achieved using Ca(NO3)2 to oxidize AVS and CaO2 to oxidize ferrous iron. After the treatment with Ca(NO3)2 and CaO2, the anaerobic reduction environment of the sediment was modified, and the metabolic pathways dominated by sulfate respiration and methanogenic metabolism in the sediment were gradually converted to nitrate-reduction and dissimilatory iron reduction. The synergy of Ca(NO3)2 and CaO2 could reduce 99.61 % CH4 compared with control check and could reduce 81.66 % N2O compared with adding Ca(NO3)2 only. Furthermore, the biodegradability of organic matter was improved due to the transformation of stubborn organic matter. These results provide valuable guidance for applying Ca(NO3)2 and CaO2 in sediment remediation.