| dc.description.abstract | Due to the fact that nitrogen pollutants in water are currently one of the most concerning contaminants, their excessive discharge can lead to environmental pollution and harm to human health. As environmental awareness gradually increases among the public in Taiwan, the government has established regulations and standards, setting stricter requirements for newly constructed wastewater treatment plants, and gradually applying higher discharge standards for already established plants. Most of Taiwan′s wastewater treatment plants currently use heterotrophic denitrification. However, for wastewater with a low C/N ratio, the denitrification efficiency is poor. Therefore, autotrophic denitrification is considered a potential replacement for heterotrophic denitrification, as autotrophic microorganisms use inorganic electron donors, eliminating the need for additional organic substances and producing less sludge.
This study selected sulfur (S0) as the electron donor. Sulfur granules not only serve as an electron donor but also as a carrier for microorganisms to grow on, forming a biofilm. During the acclimation phase, as water-soluble thiosulfate is more easily utilized by bacteria compared to solid elemental sulfur, thiosulfate was added to accelerate the growth of sulfur-oxidizing autotrophic denitrifying bacteria. After 90 days, sulfur autotrophic denitrifying bacteria were successfully cultivated.
Subsequently, using sulfur (S0) as the sole electron donor in the reactor, the optimal volumetric nitrate-nitrogen load was explored. With a hydraulic retention time of 1.48 hours and a volumetric nitrate-nitrogen load of 709.9 g NO??-N/m3·d, the denitrification rate was 60.9±7.6%. Therefore, by extending the hydraulic retention time to 1.85 hours and reducing the nitrate-nitrogen volumetric load to 567.8 g NO??-N/m3·d, the denitrification efficiency reached 80%. To evaluate the practical feasibility of the elemental sulfur denitrification system, RO concentrate was simulated as influent. Since the recalcitrant organic matter in the influent can be utilized by heterotrophic bacteria as an electron donor for denitrification, this phase achieved complete denitrification with a 100% denitrification rate.
Additionally, in the sulfur autotrophic denitrification reactor at each phase, the actual sulfate production was lower than the theoretical sulfate production, approximately 76-78% of the theoretical value. Since sulfate production is a disadvantage of sulfur autotrophic denitrification, reducing sulfate production could be a potential advantage.
From the Start-up II-ii to the Stage III-ii phase, as the electron donor transitioned from elemental sulfur and additional thiosulfate to elemental sulfur as the sole donor, the relative abundance of Thiobacillus showed a decreasing trend, while the relative abundance of Sulfurimonas gradually increased. Therefore, this study speculates that Thiobacillus seems to prefer utilizing thiosulfate, while Sulfurimonas tends to use elemental sulfur. | en_US |