Study On Sulfur/iron Autotrophic Denitrification Coupled With Anaerobic Ammonium Oxidation Process For The Treatment Of High-salt Nitrogenous Wastewater

With the fast development of marine economy,a large amount of nitrogen-laden saline wastewater caused by mariculture,seafood processing and seawater flushing is discharged into the ocean.The nitrogen-laden saline wastewater is difficult to treat by microorganisms due to high salinity,which poses a huge challenge to ecological environmental protection and governance.As a consequence,it is imperative to develop a novel biological strategy to treat nitrogen-laden saline wastewater.Halophilic marine anammox bacteria（MAB）-based sulfide-based autotrophic denitrification and anammox（MSADA）process was investigated to treat saline wastewater under different influent S/N（sulfide to nitrate）ratios.This study firstly presented a novel method with merely inoculating halophilic MAB-based sludge to start up the MSADA process in a sequencing batch reactor.Nitrogen and sulfide could be efficiently removed from saline wastewater at the total nitrogen removal efficiency of 93.7%and sulfide removal efficiency of 100%under the optimum S/N ratio of 0.75 in the MSADA process.Meanwhile,anammox and sulfide-based autotrophic denitrification respectively accounted for about 94.2%and 5.8%of the total nitrogen removal with the high nitrite accumulation efficiency of 92.7%.At the optimum S/N ratio of 0.75,Candidatus Scalindua（3.3%）,Sulfurimonas（18.7%）and Sulfurovum（11.0%）were the main functional microorganisms,which had the excellent salt tolerance.The dominating functional microorganisms dynamically changed with the different S/N ratios.The microbial community composition was similar and steady when the S/N ratios were 0.33–0.75.Nitrate reductase activity was much higher than nitrite reductase activity in the MSADA system,which made it possible to keep the NO₃^--N reduction products at NO₂^--N level and provide sufficient NO₂^--N for MAB.Halophilic marine anammox bacteria（MAB）-based Fe（Ⅱ）-driven autotrophic denitrification and anammox（MFeADA）process was investigated to treat nitrogen-laden saline wastewater under different influent Fe（Ⅱ）concentrations.Under the optimum influent Fe（Ⅱ）concentration of 150 mg/L（the molar ratio of Fe（Ⅱ）to nitrate was 0.75）in the MFe ADA process,nitrogen could be efficiently removed from nitrogen-laden saline wastewater at the total nitrogen removal efficiency of 92.6%.NH₄⁺-N and NO₃^--N removal efficiency was 100%and 86.8%,respectively.Different influent Fe（Ⅱ）doses affected the nitrogen removal process in the MFeADA process.When the influent Fe（Ⅱ）dose was 50mg/L,the nitrogen removal process was mainly performed by anammox and FeAD process in the coupling system.As the influent Fe（Ⅱ）doses increased to 100-150 mg/L,anammox,FeAD and Feammox process were responsible for the nitrogen removal process.Lastly,the influent Fe（Ⅱ）dose increased to 250 mg/L,the excessive influent Fe（Ⅱ）directly reduced NO₃^--N to N₂ by the Fe（Ⅱ）-driven autotrophic denitrification.At the optimum influent Fe（Ⅱ）concentration of 150 mg/L,Candidatus Scalindua（4.1%）,Marinicella（5.3%）and SM1A02（31.8%）were the main functional microorganisms,which had the excellent salt tolerance.The dominating functional microorganisms dynamically changed with the different influent Fe（Ⅱ）concentrations.The microbial community composition was similar and steady when the influent Fe（Ⅱ）concentrations were 50–150 mg/L.