Performance Of Nitrogen And Collaborative Phosphorus Removal Via Composite Sulfur Substrate Autotrophic Denitrification

In order to raise the effluent discharge standards of municipal sewage treatment plants and control eutrophication of water bodies,based on the sulfur autotrophic denitrification?SAD?,sulfur and different iron-sulfur minerals(FeS,Fe_1-xS,FeS₂)were respectively combined to construct three up-flow composite sulfur substrate packed bed reactors for advanced treatment of N and P,which were B1?S⁰+FeS?,B2(S⁰+Fe_1-xS)and B3?S⁰+FeS₂?,respectively.The characteristics of start-up for reactors and the effects of HRT and influent NO₃^--N concentrations on the systems were investigated.Microbial information and the processes of pollutants conversion were identified.Using the real wastewater as the influent of reactors to further investigate the practicality of the technology.The main research results are as follows:?1?Synthetic wastewater with NO₃^--N of 20mg/L and PO₄^3-P of 0.5mg/L was continuous pumped into the reactors at the HRT of 6h.B1,B2 and B3 were started successfully after 40,20 and 40 days.The removal rates of NO₃^--N for B1,B2,and B3 were respectively stabled at about 34.22%,63.11%and 27.03%,and the effluent PO₄^3--P concentrations were 0.18,0.09 and 0.26 mg/L respectively.?2?The longer HRT,the higher removal rates of NO₃^--N and PO₄^3--P.The best HRTs of B1,B2,and B3 were 12h,12h,and 9h respectively,and 20mg/L NO₃^--N was completely removed without NO₂^--N and NH₄⁺-N accumulated.In addition,the effluent PO₄^3--P concentrations of B1,B2 and B3 were about 0.11,0.02 and 0.50mg/L respectively,B3 had no obvious PO₄^3--P removal effect.?3?Due to the limitation of biomass or mass transfer rate,the removal of NO₃^--N in each reactor was gradually saturated.The maximum removal of NO₃^--N in B1,B2and B3 were 25.00,31.20 and 50.00mg/L respectively at the HRT of 12h,and the corresponding maximum removal loads of NO₃^--N were 0.047,0.057 and 0.094kg/?m³?d?respectively.PO₄^3-was removed mainly through the formation of precipitation with Fe³⁺generated by biological and chemical oxidation of minerals and adsorption complexation with Fe?OH?₃.Due to the strong self-oxidative activity of Fe_1-xS and high content of Fe,B2 effluent PO₄^3--P concentrations was always lower than 0.02mg/L,while B1 and B3 effluent PO₄^3--P concentrations were reduced to 0.06and 0.09mg/L respectively after the removal of N reached the maximum.However,B3 effluent PO₄^3--P concentrations would suddenly increase significantly,even exceed the influent PO₄^3--P concentrations,and the removal of P would fluctuate greatly.?4?NO₃^--N removal was in accordance with the half-order kinetics model,that is,the diffusion of NO₃^-from the solution through the biofilm to the surface of the sulfur substrate was the reaction limiting step.The effluent SO₄^2-concentrations were lower than the theoretical value of the SAD system,and the pH value were maintained above 6.10,which effectively alleviated the disadvantages of high SO₄^2-production and alkalinity consumption of the SAD system.?5?The microbical analysis showed that Proteobacteria was the dominant phylum,and Ferritrophicum and Thiobacillus were the dominant genus which were responsible for N and P removal.The proportions of Thiobacillus and Ferritrophicum in B1,B2,and B3 at HRT phases were 16.07%,30.07%,30.20%and 31.24%,50.19%,11.62%,respectively.The proportions of Thiobacillus and Ferritrophicum in B1,B2,and B3 at influent NO₃^--N phases were 41.39%,35.60%,10.56%and 35.75%,35.90%,29.00%,respectively,the biomass observed also showed FeS>Fe_1-xS>FeS₂,which were consistent with the results of the genus abundance.A small amount of heterotrophic denitrifying bacteria were also detected.However,more anaerobic heterotrophic denitrifying bacteria and fermentation bacteria were detected in B3 with Anaerolineaceae of 7.16%and Denitratisoma of 11.59%,which improved the removal ability of NO₃^--N for B3 at influent NO₃^--N phases.?6?The reactors also showed better removal effects for real wastewater.When the effluent NO₃^--N concentrations of wastewater treatment plants were 42.39 and16.58mg/L respectively,the effluent NO₃^--N concentrations of B1,B2 and B3 were30.41,25.24,21.12mg/L and 6.46,0.61,0.54mg/L respectively.Wastewater treatment plant effluent PO₄^3--P concentrations were always around 0.5mg/L,B1 and B2 had a very stable removal of P,and effluent PO₄^3--P concentrations were about 0.06 and0.02mg/L respectively,while B3 effluent PO₄^3--P concentrations varied greatly.?7?The technology was feasible for advanced treatment of secondary effluent,which improved the biological oxidability of traditional iron-sulfur minerals.The performance of N and P removal were B3>B2>B1 and B2>B1>B3,respectively.In summary,B1 and B2 can be used for the simultaneous removal of low concentration N and P,while B3 can adapt to a wide concentration range of NO₃^--N changes.