Investigation Of The Noval AASO Process Based On Sulfur Autotrophic Nitrogen Removal

In recent years,in order to reduce water pollution,sewage discharge standards have become increasingly strict with nitrogenous substances.At present,the traditional A~2O process widely used for nitrogen and phosphorus removal belongs to a single mud system.Since microbes with different function and physiological properties are completely mixed in the activated sludge process,they have to encounter adverse conditions in some phases and compete for substrates and ecological niche,thus retain relative low abundance of functional microbes and present relative low removal efficiency of COD,nitrogen and phosphate.Moreover,insufficient carbon sources in influent might limit its nitrogen removal efficiency in the A~2O process fed with low-carbon-to-nitrogen ratio wastewater.How to effectively and efficiently improve the nitrogen removal with the traditional A~2O process is the current hotspot of water treatment technology.Sulfur autotrophic denitrification can reduce the demand for carbon sources,and produce less residual sludge,which has been recognized as the most promising wastewater treatment process.However,there are still few studies on the application of sulfur autotrophic denitrification in the treatment of domestic sewage with low sulfate content.In this study,the traditional A~2O process was improved by optimizing the enrichment of nitrogen removing microorganisms and coupling with sulfur autotrophic denitrification.A new double sludge AASO process was designed by introducing membrane module to separate anaerobic-anoxic and aerobic sludge.The new AASO process was started and operated in laboratory to investigate its nitrogen removal properties with influent of low carbon/nitrogen ratio.On this basis,combined with the analysis of physical and chemical parameters of water quality in different stages,as well as the microbial population structures and metabolic characteristics,the metabolic mechanism of sulfur autotrophic denitrification in this AASO process was discussed.At the same time,the membrane fouling characteristics of mixed liquid in different stages of AASO process were analyzed in order to provide theoretical reference for the practical application of this noval process.The main research conclusions are listed as follows:(1)The new AASO process can effectively perform sulfur autotrophic denitrification in the treatment of low sulfate concentration wastewater.The COD removal rate of the AASO process was maintained at about 80%during the entire operation phase.In the late operation period,the ammonia nitrogen removal efficiency was as high as 84%,the ammonia nitrogen concentration in the effluent was less than 5 mg/L.During the entire operation period,the nitrate produced by ammonia oxidation was completely removed in the anoxic tank.(2)According to the analysis of high-throughput sequencing results,the dual-sludge operation mode of the AASO process was conducive to enrich different functional microorganisms in the anaerobic-anoxic and aerobic stages respectively.With the operation of the reactor,a relatively stable functional microbial community were developed in the AASO process gradually,and sulfur reduction and sulfur oxidation microorganisms dominated in the anaerobic and anoxic tanks.In order to enhance the ammoxidation in the aerobic tank,the predominant flora transformed from Desulfobacter,Sulfurovum and Sulfuricurvum to Sulfurospirillum and Sulfurimonas in anaerobic and anoxic tank after adjusting the operating conditions.The gene analysis of sulfate reducing bacteria showed that nap and nos denitrification genes contained in sulfurospirillum may be the main reason for its dominant position after adjustment,wherea the dominant sulfur oxidizing bacteria before and after adjustment all contained functional genes required for nitrate reduction.(3)The membrane fouling potential of the mixed liquid from each phase of AASO process were determined by constant pressure membrane flux test,three-dimensional fluorescence spectrum,size exclusion chromatography and infrared spectroscopy.The results shown that the membrane flux of the aerobic liquids was much higher than those of the anaerobic and anoxic phases,and the dissolved organics is the lowest,which is consisted mainly with the macromolecular inert humic acid and microbial metabolites,thus lead less membrane fouling potential.On the contrary,the liquids from anaerobic and anoxic phases contained a large amount of dissolved organics,mainly in form of protein-like substances,which was easily to cause membrane fouling.Therefore,in practical,the membrane module is preferably applied for the solid-liquid separation in the aerobic stage.