Study On The Coupling Process Of Sulfate Reduction And Sulfur Autotrophic Denitrification For Advanced Nitrogen Removal

Due to the increasingly strict sewage discharge standards in China,under the background of improving quality and efficiency in most urban sewage treatment plants,advanced denitrification of secondary effluent is an urgent problem that needs to be solved.It is necessary to conduct researches on advanced denitrification processes.In recent years,sulfur autotrophic denitrification process has attracted extensive attention due to its advantages of high TN removal efficiency,good effluent quality,low operating cost and low sludge production.In order to make full use of the sulfate in the secondary effluent of urban sewage plants as the sulfur source for sulfur autotrophic denitrification,it is proposed a sulfate reduction coupling sulfur autotrophic denitrification process to reduce sulfur source consumption and reduce operating costs.The main research findings were as follows:1)First,a sulfate reducing bacteria SRB was isolated by the plate scribing method,and identified as Desulfovibrio desulfuricans by 16S r DNA molecular biology.On this basis,SRB was used in the sulfate reduction experiments based on the slow release carbon source.The best sustained-release carbon source filler was the starch and polyvinyl alcohol（PVA）prepared by freezing method with a mass ratio of 7:3（FSP-1）.The concentration of SO₄^2-in the influent of the static batch experiment was 180 mg·L^-1,and the highest SO₄^2-reduction efficiency could reach 65.56%,and the highest S^2-generation amount was 25.92 mg·L^-1.The dynamic small-scale experiment showed that when the average concentration of SO₄^2-was 183.53 mg·L^-1 in influent,the highest reduction efficiency of SO₄^2-was 82.98%,and the generation of S^2-in the effluent was between 15.26～43.17 mg·L^-1.2)The sulfur autotrophic denitrification experiment with sulfide as the sulfur source（electron donor）showed that the optimal operating parameters were initial p H value 7.05,temperature 31.98℃,and molar ratio of N to S（N/S）0.75 based on the response surface methodology.When the influent TN was 50 mg·L^-1,the denitrification efficiency reached95.53%.The dynamic small-scale experiment under optimum conditions showed that the influent TN concentration was 30 mg·L^-1 and HRT was 5 hours,stable operation was achieved after 10 days,and the highest TN removal efficiency reached 94.31%.The dominant genus of bacteria in the upper,middle and underneath sludge of the reactor was Thiobacillus,with relative abundance ratios of 49.99%,46.31%,and 46.39%,respectively.3)Based on the above research,a sulfate reduction（SR）-sulfur autotrophic denitrification（SAD）coupled denitrification process was developed.When using the simulate wastewater as processing object,the average values of COD and TN in influent was 36.04 mg·L^-1 and 19.30 mg·L^-1,respectively,the average values of COD and TN in effluent after 10 hours of HRT were 16.17 mg·L^-1and 1.48 mg·L^-1,respectively.The average values of COD and TN in the effluent after 5 hours of HRT were 19.07 mg·L^-1 and 1.49mg·L^-1,respectively.The average values of COD and TN in the effluent after 2.5 hours of HRT were 22.48 mg·L^-1 and 5.05 mg·L^-1,respectively.The system had a certain COD removal efficiency,a high TN removal efficiency,and stable operation.When using the actual secondary wastewater as processing object,the average values of COD and TN in the influent were 33.15 mg·L^-1 and 19.91 mg·L^-1,respectively.When the HRT was 5 hours,the average values of COD and TN in the effluent were 27.23 mg·L^-1 and 3.07 mg·L^-1,respectively,meeting the requirements of first-class A standard.The main functional bacteria in the SR reactor were still the inoculated Desulfovibrio,while Thiobacillus was the main dominant genus at the SAD reactor genus level.