Index for nitrate dosage calculation on sediment odor control using nitrate-dependent ferrous and sulfide oxidation...

Nitrate-driven sulfide and ferrous oxidation have received great concern in researches on sediments odor control with calcium nitrate addition. However, interrelations among sulfide oxidation, ferrous oxidation and their associated microbes during the nitrate reduction process are rarely reported. In this work, a n_NO3/n_(S+Fe) ratio (mole ratio of NO₃^- concentration to S^2- and Fe²⁺ concentration) was first introduced as an index for calcium nitrate dosage calculation. Then certain amount of calcium nitrate was added to four sediment systems with various sulfide and ferrous initial concentration to create four gradients of n_NO3/n_(S+Fe) ratio (0.6, 0.9, 1.5 and 2.0) for treatment. Furthermore, the significant variations of sulfide and ferrous oxidation, microbial diversity and community structure were observed. The results revealed that at low n_NO3/n_(S+Fe) ratio (0.6 and 0.9) systems, sulfide seemed prior to ferrous to be oxidized and no obvious ferrous oxidation occurred. Meanwhile, sulfide oxidizing associated genus Sulfurimonas sp. became dominant in these systems. In contrast, sulfide and ferrous oxidation rate increased when n_NO3/n_(S+Fe) ratio reached 1.5 and 2.0 (two and three times of theoretically required amount for sulfide and ferrous oxidation), which made Thiobacillus sp. more dominant than Sulfurimonas sp. Hence, when n_NO3/n_(S+Fe) ratio of 1.5 and 2.0 were used, sulfide and ferrous could be simultaneously oxidized and no sulfide regeneration appeared in two months. These results demonstrated that for sulfide- and ferrous-rich sediment treatment, the nitrate consumed by ferrous oxidation should be taken into account when calculating the nitrate injecting dosage. Moreover, n_NO3/n_(S+Fe) ratio was feasible as a key parameter to control the oxidation process and as an index for calcium nitrate dosage calculation.