Influence Of Hydraulic Loading On Sulfur-based Autotrophic Denitrification For Micro-polluted Water

The environmental problem is increasingly more serious in recent years, especially the eutrophication of lake in the south, which showed mainly limit-exceeding problems of nitrate. Traditional denitrification process includes limitations, because of adding a large amount of carbon source. Denitrification technology has been receiving more and more attention. Due to its advantages of needing no organic carbon addition, causing no second contamination and easier sludge proposal, recently sulfur-based autotrophic denitrification has been well studied for the micro-polluted water with low C/N ratio. But it still at its preliminary stage. Sulfur-based autotrophic denitrification which adopts the thiosulfate as electron donor was applied to treat the low concentration nitrate-contaminated water, and combined with biological filter. In order to provide technical reference for practical engineering.Removing nitrate as the goal, thesis mainly studies hydraulic loading have an effect on the treatment by biological filter, and explores its design parameters. Which provides theory basis for the design and operation. The main conclusions were drawn as follows:Anaerobic sludge was more suitable than the aerobic excess sludge for the seed sludge of autotrophic denitrification. It needed much less time to start up a new reactor, due to the ammonia release from the excess sludge.Different ceramsites fillers under the same condition caused not much difference to the nitrate removal.Two column reactors of the same volume with the ratio of height to diameter 5.7 and 16.1, one slim and another short, were used to compare the denitrification-performance. At last, the shortest HRT and largest hydraulic loading were determined. The results showed that the short is more stable technology than the slim when hydraulic loading is less than 1.0 m3/(m2·h), however the slim can achieve more better treated effect when hydraulic loading is more than 1.0 m3/(m2·h). The shortest HRT and largest hydraulic loading of the short reactor were 0.5 h and 1.0 m3/(m2·h), and the average removal rate of TN and NO3-- N were 83% and 89%, respectively. For the slim reactor, the shortest HRT and largest hydraulic loading could achieve 10 min and 6.0 m3/(m2·h), meanwhile the average removal rate of TN and NO3-- N remained 83% and 94% without the accumulation of nitrite.SEM observation was made on the sludges and ceramsite from the reactors. It verified that the filament-shaped bacteria predominated in the reactors, and that much higher bacterial population was found in the flocculent sludge than on the surface of ceramsite.Molecular biology analysis revealed that the Thiobacillus in the systems accounted for 8.4%, becoming one of the dominant species. The porportion of different denitrifiers changed in the system with the increase of hydraulic loading. The porportion of Thiobacillus gradually decreased, while the newly found speices Thiothrix and Sulfurimonas increased. These findings indicated that the relatively high NO3--N concentrations and low hydraulic loading may benefit the growth of Thiobacillus, while Thiothrix and Sulfurimonas might survive even lower substrate concentration and swifter water flow.