Characteristics Of Nitrogen And Sulfide Removal In Anaerobic Reactors And It’s Microbial Community Diversity

This article mainly focuses on the target of reducing sulfide and nitrate effluent concentration and improving the conversion rate of sulfur and nitrogen in the anaerobic denitrification and de-sulfide treatment process. The influences of the N/S ratio, Hydraulic Retention Time(HRT), the electron acceptor type, sulfide load and the influent pH on selective removal of nitrogen and sulfide in anaerobic denitrification and de-sulfide treatment were mainly studied, and the optimal control conditions in anaerobic denitrification and de-sulfide treatment process are obtained. The main results are listed as follows:(1)When nitrate was acted as electron acceptor in the reactor, the optimal N/S ratio for the removal of sulfide in the system was 0.67; the N/S ratio for the removal of nitrate was 0.67~1.0, and N/S ratio of 0.5 was benefit for the production of sulfur; It was obviously that simultaneous desulfidation and denitrification process occured by controlling the N/S ratio be 0.5~1.0. While in the system where nitrite was served as electron acceptor, the optimum N/S ratio was 0.67 for sulfide removing, and the optimal one was 0.2~1.0 for nitrite removing, and all the removal rate reached at least 99%. The denitrification process would not be suppressed and the removal rate of nitrite was higher than that of nitrate. It was indicated nitrite was a suitable electron donor for denitrification in the nitrite system.(2)In the system, nitrate was acted as electron acceptor, the N/S ratio for the production of sulfur was 0.50, and the corresponding percentage of the selective sulfur production was 24% while the selective sulfate production was 30%, in addition the HRT should be controlled at 24 h. The highest selective nitrogen formation yield was 58 mL at N/S=1.0. While in the nitrite system, the optimal N/S ratio was 0.67 for sulfide removing and the corresponding selective sulfur formation percentage and sulfate formation percentage was 11.01% and 53.58%, respectively; the optimal N/S ratio for nitrogen production was 2.0 with 74 mL nitrogen. It was showed that the selectivity for sulfur formation was more apparent to the electron acceptor; the sulfur production by nitrate was higher than that of nitrite. The nitrogen production was obviously different in the two systems indicating that the transformation way may be different. Nitrate was mainly removed by autotrophic denitrification while nitrite was mostly removed by anaerobic ammonia oxidation and heterotrophic denitrification.(3) The outflowing sulfide concentration was lower than 4.2mg/L and the sulfide removal rate were higher than 98% after 24 h reaction when the influent sulfide concentration was 150~350mg/L at 1.0~2.0 N/S ratio. The desulfuration process was suppressed when the influent sulfide concentration was raised up to 400mg/L. The effluent nitrate concentration will be lower than 14mg/L and the removal rate was all above 70% when the N/S ratio was 0.5~0.67, influent sulfide concentration was between 150 to 250mg/L and the HRT was 24 h. The denitrification would be suppressed after raising the inflowing the sulfide concentration to 300mg/L. It was showed that denitrification will be suppressed when the influent sulfide concentration was higher than 250mg/L while the desulfidation will not be suppressed until the sulfide concentration was 350mg/L.(4) The selective sulfur formation percentage can be as high as 33.2%, and the corresponding selective formation percentage of sulfate was about 36.04% under the condition that sulfide concentration was 250~400mg/L and the N/S ratio was 1.0. It is more easily for the formation of sulfur by raising the influent sulfide concentration. The highest selective nitrogen formation yield was 64 mL at N/S=0.5 with influent sulfide between 150 to 300mg/L. The electron equilibrium was balanced when the influent sulfide concentration was 150~350mg/L and N/S ratio was 1.0. It is not good for the selective nitrogen formation at high sulfide load and high N/S ratio.(5) The optimal influent pH for the removal of sulfide is 7.5~8.0 and the one turned to be 8.5~9.0 in nitrate removing when the influent sulfide concentration was 200mg/L and HRT was 24 h. while at the condition when the influent sulfide concentration was 300mg/L and the HRT was 48 h, the optimal influent pH for the removal of sulfide and nitrate was 7.5~9.0 and 8.5~9.0, selectively.(6)The optimal influent pH was 7.5~8.0 for sulfur formation, the selective sulfur formation percentage can be as high as 30%, and the corresponding selective formation percentage of sulfate was about 10.21% in different sulfide loading systems. The optimal influent pH should be 8.5~9.0 for the selective formation of nitrogen after the reaction for 24 h, and the maximum nitrogen production can reach 60 mL.(7)The desulfurization and denitrification functional microorganisms in the reactor were Sulfurovum and Kluyvera cryocrescens. The drastic reduction of biodiversity would happened by increasing the influent sulfide concentration and influent pH simultaneously.