Study On The Behavior And Mechanism Of Nitrogen And Phosphorus Removal In Wastewater By Pyrite

With the constant development of industry and agriculture in China,the degree of eutrophication of water body is increasing year by year,which seriously restricts the sustainable development of social economy and environment in China.The sources of nitrogen and phosphorus that cause eutrophication of water are very extensive,mainly for industrial,agricultural and urban domestic sewage.Traditional heterotrophic denitrification process has achieved good results in the treatment of high concentrations of nitrogen and phosphorus sewage,however heterotrophic denitrification has a high demand for C/N.Generally,it is considered that effective denitrification can be achieved only when the C/N ratio reach to 7-8,and it is difficult to meet the requirements of normal water bodies.Therefore,autotrophic denitrification technology has been widely studied,although sulfur autotrophic denitrification has higher efficiency of denitrification efficiency,the removal rate of phosphate is negligible.Therefore,it is of practical significance to research and develop the technology,simultaneous removal of nitrogen and phosphorus by pyrite in micro-polluted water.In order to remove nitrogen and phosphorus from micro-polluted water(eutrophication)and sewage treatment plant secondary effluent,this paper adopts the method of autotrophic denitrification with pyrite,Studied the behavior and mechanism of nitrogen and phosphorus removal in wastewater by pyrite.The main contents and conclusions of this study are as follows:(1)Batch tests were carried out for pyrite from Yunfu(Py-Y)in Guangdong Province and Tongling(Py-T)in Anhui Province.The study have found that Py-T can not be used by microorganisms for autotrophic denitrification,while Py-Y can effectively autotrophic denitrification.The main parameters affecting denitrification were studied with Py-Y.When Py-Y/L ratio is 1:0,denitrification completely inhibited,and when Py-Y/L=3:1,denitrification removal rate is the fastest,the average removal rate of 3.50 mg-N/L·d.The study on the initial pH value found that high denitrification rate under the near neutral conditions,high pH will cause a certain concentration of nitrite accumulation.Ammonia nitrogen concentration has a certain effect on denitrification,the limiting concentration of ammonia nitrogen is about 1.4 mg/L;when the influent phosphate concentration was 0 mg/L,the nitrite nitrogen accumulation was up to 15.07 mg/L,which seriously affected the denitrification rate.The limiting concentration of phosphate was about 0.5 mg/L;when the temperature is 20-30℃,the denitrification efficiency is about 95%,and the higher the temperature,the better the removal of phosphate;the different particle sizes and the quality of pyrite are the same effect on denitrification and phosphorus removal.All of them affect the denitrification and phosphorus removal rate by providing the surface area to which the microorganisms adhere.The larger surface area,the better denitrification and phosphorus removal.During the whole process,more denitrifying bacteria are in suspension growth.The proliferation of microorganisms accompanies the oxidation of pyrite.(2)In the study of the start-up mode of the anaerobic reactor Py-Y,both the dynamic start-up and the static start-up can achieve the purpose of starting the reactor normally.Statically starting the reactor,the microorganisms are evenly distributed within the reactor,and the method is simple,but takes a long time.The dynamic start-up can quickly start the reactor and enable the microorganisms to better adapt to the flow state of the water,and the amount of microorganisms decreases along the direction of the water flow.(3)When the influent pH value is about 7±1 of pyrite anaerobic reactor,the reactor has a high nitrogen and phosphorus removal efficiency.When the pH value is low,it will be detrimental to denitrification and easily lead to the accumulation of nitrite.Influent pH value is too high to seriously affect phosphate removal.When the concentration of ammonia nitrogen in the reactor was zero,the denitrification process was severely suppressed,resulting in the accumulation of nitrite,and the minimum concentration of ammonia nitrogen was 1.4 mg/L.When the alkalinity value in the influent water is zero,a large amount of nitrate and nitrite are accumulated,and the removal rate of total oxidizing nitrogen(TON)is about 54.9%.Overall,the influent alkalinity value should be maintained around 100 mg/L.When studying the effect of phosphate concentration on nitrogen and phosphorus removal,it can be clearly seen that when the phosphorus concentration is zero,it is easy to cause the accumulation of nitrite,and the total oxidizing nitrogen almost undiminished,showing that a certain concentration of phosphorus in the water is very necessary.(4)When the reactors(Py-Y and Py-T)were started,the microbial community structure was dominated by Sulfurimonas and Thiobacillus,both of which had denitrification using pyrite.With the developing of the reactors,the species of microorganisms were increased in the reactor,but the abundance of bacteria with denitrification capacity decreases.(5)There are some differences in the ability of pyrite to provide electrons for the autotrophic denitrification of different lattice structures.From the results of XPS analysis,it can be seen that the chemical states of the iron and sulfur proportion on the surface of the two pyrite(Py-Y and Py-T)are basically the same.However,from the results of TEM analysis,pyrite Py-Y and Py-T have different lattice structures.Py-Y is polycrystalline structure.The major crystal planes include(220),(211),(111),and Py-T is a single crystal structure and the crystal plane is mainly(100),(110)and(210).The(100),(110)and(210)surface of single crystal pyrite Py-T is more stable than the(220),(211)and(111)surfaces of polycrystal pyrite Py-Y,and the total energy of(100),(110)and(210)surface is higher than that of(220),(211),(111)surface.