Mechanism of ammonium sharp increase during sediments odor control by calcium nitrate addition and an alternative...

Nitrate-driven sulfide/ferrous oxidation has been proved a cost-effective approach for river sediments in-situ odor control. However, calcium nitrate addition would sharply increase ammonium concentration in interstitial water and the mechanism was not yet clear. In this work, though sulfide and ferrous iron were efficiently oxidized, about 102% of NH₄⁺ concentration increased in interstitial water on the first day of calcium nitrate injection (30 mg kg dwt^-1), and about 31% more NH₄⁺ increase at the 21st days was observed. To discover the mechanism of ammonium sharp release, desorption kinetics experiment was conducted and the results suggested that the short-time sharp releases of ammonium when calcium nitrate was added could be attributed to the chemical extraction of exchangeable ammonium by calcium ion. Furthermore, at the end of treatment, many genus such as Thiobacillus, Sulfurimonas, Thermomonas, and Clostridium, which were closely related to sulfide and ferrous-driven denitrification and dissimilatory nitrate reduction to ammonium (DNRA), were identified by 16S rRNA Illumina sequencing method. These findings indicated the long-time increase of ammonium might be determined by the biochemical processes (e.g. DNRA) driven by nitrate reduction. Therefore, to avoid the impact of ammonium release, an alternative subsurface injection method was introduced in this work, and the results showed that ammonium releases could be well controlled when the injection position was beneath 10 cm of the sediment surface.