Effects Of Na₂S₂O₃-type Sulfur Autotrophic Denitrification On Medium Salinity And Its Effect On Deep Denitrification Of Reclaimed Water In Colleges And Universities

With the increasing demand for sewage treatment,regeneration and reuse,the quality requirement of reclaimed water was also increased.The study found that in the process of recycling water in colleges and universities,there is a problem of accumulation of NO₃^--N,which has the risk of causing eutrophication of water bodies.Autotrophic denitrification does not require organic carbon sources and biological growth is slow,which has the advantages of saving resources and low sludge yield.The thesis studied the effect of Na₂S₂O₃ sulfur autotrophic denitrification in deep denitrification of reclaimed water in colleges,and investigated the effect of salinity on Na₂S₂O₃ sulfur autotrophic denitrification.The research contents include the cultivation and enrichment of sulfur autotrophic denitrifying sludge,the start-up and operation of two different packing reactors,the optimization of experimental operation parameters,and the deep denitrification effect on water in colleges.The nitrification process provides theoretical guidance in the direction of deep denitrification of reclaimed water in colleges.The main conclusions are as follows:（1）The SBR reactor was inoculated with activated sludge from a reclaimed water station in a university,and Na₂S₂O₃ was used as the electron donor.The sulfur autotrophic denitrification sludge was successfully cultured in about 20 days,the domesticated microorganisms were mainly bacilli.（2）Activated carbon and polyurethane sponge were used as fillers to start up-flow anaerobic filter column reactors,and operated under the same conditions to compare the denitrification effects of the two fillers.The results were showed that:Polyurethane sponges were more easily attached to microorganisms than activated carbon,can form biofilms more quickly,and had a shorter start-up time.The microorganisms in the reactor were mainly rod-shaped and spherical,and the main bacteria genera were Thiobacillus,Sulfurimonas,Ferritrophicum,and the abundance of dominant bacteria gradually decreased along the water flow direction in the reactor;Reduced the HRT to increase the influent load.During the process of reducing the HRT from 6h to 2h,the NO₃^--N removal rate of the two groups of reactors is above 94%,but when the HRT was reduced to 0.5h,the NO₃^--N removal rate of the activated carbon reactor was reduced to 70%,and that of the polyurethane sponge packed reactor was reduced to 80%.The denitrification capacity of the polyurethane sponge packing reactor is slightly higher,and the sludge retention capacity is better.（3）The effects of SO₄^2-and Cl^-concentration on the activity of sulfur autotrophic denitrifying bacteria were studied by batch reactor.The results showed that both SO₄^2-and Cl^-concentration would reduce the denitrification efficiency:When the SO₄^2-concentration was0～4 g/L,the NO₃^--N removal rate was 97%,the denitrification rate was 0.00162 g N·（g SS·h）^-1,and the SO₄^2-concentration was 15 g/L,the NO₃^--N removal rate was reduced to 51%,the denitrification rate was 0.00086 g N·（g SS·h）^-1,and the sludge activity was reduced by 50%compared with the initial stage;When the Na Cl concentration was lower than 30g/L,the NO₃^--N removal rate was higher than 97%,and the denitrification rate was 0.00165 g N·（g SS·h）^-1.As the Na Cl concentration increased to 80g/L,NO₃^--N removal rate was reduced to 34.6%,denitrification rate was 0.00061 g N·（g SS·h）^-1,which decreased by 63%compared with the initial stage,and the sulfur autotrophic denitrifying bacteria lost most of their activities;The adaptability of sulfur autotrophic denitrifying bacteria to salinity was studied by continuous operation.When the Na Cl concentration increased to 50 g/L,the NO₃^--N removal rate decreased to 78%at first,and the reactor performance recovered after running for 16 days;High-throughput sequencing showed that the abundance of Proteobacteria was relatively stable at the phylum level in the sulfur autotrophic denitrification system with the increase of salinity,while the abundance of Bacteroidetes decreased from 8.73%to 1.69%with the increase of salinity,the content of Chloroflexi increased with the increase of salinity.At the genus level,the abundance of Sulfurimonas was negatively correlated with the increase of salinity,in the process of increasing salinity,the abundance of Thiobacillus first increased and then decreased.（4）The optimization results of autotrophic denitrification operation parameters of continuous flow anaerobic filter column show that:when the NO₃^--N concentration is 40～50g/L,the optimum S/N of sodium thiosulfate autotrophic denitrification system is 1,and the optimum p H is 7～8,and the optimum temperature is 32°C;The experiment carried out in-depth denitrification research on reclaimed water in colleges through autotrophic and autotrophic coupled heterotrophic methods.The results showed that:When Na HCO₃was not added to the influent,the alkalinity required for sulfur autotrophic denitrification could not be maintained,the TIN removal rate was only 54%,and NO₂^--N was accumulated.After Na HCO₃ was not added to the influent,the TIN removal rate was 90%.Autotrophic coupled heterotrophic synergistic denitrification can reduce the alkalinity requirement of the reactor and reduce the effluent sulfate concentration.Under the condition of no added alkalinity,adding sodium acetate to remove NO₃^--N heterotrophic denitrification in reclaimed water 0,1/10,1/5,1/3,2/5 of the theoretical value,The removal rates of TIN were54.0%,60.8%,75.2%,and 96.0%,respectively.The average p H of the effluent was 5.24,5.86,6.66,7.33,and 7.83,respectively.The SO₄^2-concentration of the effluent was also reduced from 269.8 mg/L to 226.75 mg/L.