Abstract
The adsorption and utilization of Fe(Ⅲ) can be impeded by precipitation in anaerobic reactors. In this study, we investigated whether the bioavailability of Fe(Ⅲ) can be enhanced by EDTA-Fe(Ⅲ), thereby improving the stability of anammox system. Fe(Ⅲ) and EDTA-Fe(Ⅲ) were added to two parallel up-flow anaerobic sludge blanket (UASB) reactors, respectively. After 186 days of operation, when the nitrogen loading rate (NLR) was 0.8 g-N/L/d, the nitrogen removal rate (NRR) of R2 was stable at 0.675 g-N/L/d, which was higher than that of R1 at 0.557 g-N/L/d. The anammox activity of R2 reached its peak in phase Ⅲ (158.55 ± 4.53 mg-N/g-VSS/d), while the anammox activity of R1 was only 28.37 ± 5.96 mg-N/g-VSS/d. Moreover, in phase Ⅱ-Ⅴ, the bioavailability of Fe(Ⅲ) in R2 was increased by 15.63%, 38.37%, 65.90%, and 39.63%, respectively, compared with R1. The results showed that EDTA-Fe(Ⅲ) can prevent precipitation encasing anammox granular sludge, which can enhance substrate transport and Fe(Ⅲ) adsorption utilization. High throughput sequencing suggested that EDTA-Fe(Ⅲ) could better increase the abundance of anammox bacteria (AnAOB). In conclusion, this research proved that EDTA could increase the bioavailability of Fe(Ⅲ) and thereby ensuring the stability of the reactors.
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