Effects Of Phosphorus And Sulfate On Sulfur Autotrophic Denitrification And Its Denitrification Effec

Reclaimed water is an important source of ecological recharge water in rivers,and there are still great differences in total nitrogen standards between them.Studies have shown that excessive NO₃^--N and NH₄⁺-N in the water will change the nitrogen balance of the system,which is one of the reasons for the eutrophication of the water body.The reclaimed water presents the characteristics of low carbon and high nitrogen after deep treatment,and most of the nitrogen sources exist in the form of NO₃^--N.Phosphorus can be removed by precipitation in the primary treatment of wastewater.The high solubility and hydrophilicity of nitrogen lead to its residual in wastewater,which leads to the unsynchronized removal of nitrogen and phosphorus,resulting in the water quality characteristics of low phosphorus and high nitrogen.Sulfur autotrophic denitrification is widely used in low C/N ratio wastewater treatment due to its low carbon efficiency,small land occupation and low sludge production.Based on this,the sulfur autotrophic denitrification process was applied to the deep denitrification of reclaimed water in this study.Firstly,the nitrogen and sulphur packed autotrophic denitrification filter column was constructed.The effect of the presence of phosphorus in water on the initiation of film hanging and denitrification of autotrophic denitrification columns was investigated by monitoring the purification effect of elemental nitrogen in simulated reclaimed water.Secondly,the effect of SO₄^2-accumulation on deep nitrogen removal by sulfur autotrophic denitrification filter column was explored.Finally,the deep denitrification effect of the reactor in the presence of carbon source was explored by treating the actual reclaimed water.This study can provide guidance for the application of the sulfur autotrophic denitrification process in deep nitrogen removal of reclaimed water.The main results and conclusions are as follows:（1）Monitoring of water quality in the effluent of autotrophic denitrification columns initiated under phosphorus-limited and phosphorus-sufficient conditions.The results showed that the autotrophic denitrification column had good denitrification effect and relatively short start-up time under phosphorus-sufficient conditions,with an average removal rate of 98.25%and 97.11%for NO₃^--N and TIN respectively.The best nitrogen removal effect was achieved by controlling the HRT at 4 h under phosphorus-sufficient conditions,and the average NO₃^--N removal rate was stable at over 93%without NO₂^--N accumulation.Activated carbon particles in autotrophic denitrifying filter column were more conducive to microbial attachment and growth,and Thiobacillus,Sulfurimonas,and Ferritrophicum were the dominant bacteria.The abundance of the dominant genus decreased with the direction of water flow.（2）Appropriate addition of phosphorus sources was helpful to improve the nitrogen removal efficiency and impact load resistance of autotrophic denitrification filter column under phosphorus-limited,and the improvement of the two abilities was related to the relative abundance of dominant bacteria in the system.Under the conditions of N/P=83,HRT=4 h,the removal efficiency of NO₃^--N was the best when the concentration of NO₃^--N was 30～50mg/L,and the average removal rate was over 96%.Adding 0.36 mg/L,0.75 mg/L,1.2 mg/L phosphate（N/P:83,40,25）,the average removal rate of NO₃^--N increased from 73.22%to81.71%under the condition of HRT of 2 h.Pseudomonas was the dominant genera under phosphorus-limited conditions,Ferritrophicum and Thiobacillus were the dominant genera under phosphorus-sufficient conditions,and the dominant genera change from mixotrophic to fully autotrophic.（3）The results of monitoring effluent quality of autotrophic denitrification filter column under SO₄^2-accumulation showed that sulfur autotrophic denitrification system had certain tolerance to SO₄^2-,but the high concentration of SO₄^2-would affect the denitrification effect.When the concentration of SO₄^2-in simulated wastewater was 0 g/L,4 g/L,6 g/L,8 g/L and 15g/L,the average removal rates of NO₃^--N were 98.01%,97.85%,94.85%,92.42%and 85.48%,respectively.The accumulation of SO₄^2-would inhibit the abundance of Bacteroidetes and Chloroflexi,while the abundance of Proteobacteria was positively correlated with the increase of SO₄^2-concentration.With the increase of SO₄^2-concentration,Denitratisoma replaced Thiobacillus and Ferritrophicum as the dominant bacteria.（4）Enhanced autotrophic denitrification could be achieved by adding sodium acetate as a carbon source to the actual reclaimed water at a dosage greater than 1/4 of the required theoretical value.When the concentration of sodium acetate was 0 mg/L,21.96 mg/L,27.45mg/L,36.6 mg/L（theoretical value of 0,1/5,1/4,1/3）,the average removal rate of TIN increased from 69.59%to 97.68%,the average pH of effluent increased from 6.04 to 7.68,and the concentration of SO₄^2-in effluent decreased with the increase of sodium acetate dosage.The effluent quality met the requirements of"The Reuse of Urban Recycling Water—Water Quality Standard for Scenic Environment Use"（GB/T18921-2019）.