Study On The Performance Of Deep Removal Of Ammonium And Phosphorus Through Denitrification Of Polylactic Acid And Pyrrhotite

At present,there are disadvantages such as the need to add carbon sources,high control costs,and poor phosphorus effect.Therefore,it is of great significance to develop a set of low costs and environmentally friendly deep-nitrogen removal and phosphorus removal technology.In this study,polylactic acid was used as a solid carbon source for heterotrophic denitrification and pyrrhotite was used as an autotrophic denitrifying electron donor for nitrogen and phosphorus removal.Firstly,the optimal molecular weight of polylactic acid was screened,polylactic acid denitrification reactor was built,and then polylactic acid-pyrrhotite composite packing was used to synergize denitrification to explore the optimal experimental conditions for nitrogen and phosphorus removal,which provided a theoretical basis for the practical application of composite filler.1.The static carbon release and denitrification properties of polylactic acid as denitrifying solid carbon sources with different molecular weights,as well as the nitrogen and phosphorus removal performance of polylactic acid denitrification column reactor under different experimental conditions,were investigated.In terms of static carbon release,the carbon release of polylactic acid of each molecular weight was relatively stable.The denitrification effect of polylactic acid with a molecular weight of 5000 g/mol was better than that of polylactic acid with a molecular weight of 10000 g/mol and a molecular weight of 50000 g/mol in a 36-day static denitrification experiment.The film initiation period of the reactor with 5000 g/mol molecular weight polylactic acid as filler was 20 d.The experimental results show that the nitrogen removal effect of each column reactor is the best when the hydraulic residence time(HRT)is 24 h and the nitrate nitrogen influent concentration is 40 mg/L.The concentration of phosphate in the influent water affects the denitrification effect of the polylactic acid column reactor to a small extent.The effluent COD showed a gradual downward trend,and the maximum did not exceed 80 mg/L.In the experiment,it was found that the phosphorus removal effect of the polylactic acid reactor was poor,and it could only rely on a small amount of phosphorus removal microorganisms in the biofilm to remove phosphorus.Through scanning electron microscopy,it was found that the surface of polylactic acid particles was smooth,with fewer pores,and there was almost no function of adsorbing phosphate.After the experiment,the SEM image of polylactic acid showed that a small number of microorganisms were attached to it,and the surface was corroded by microorganisms to create holes.2.The denitrification and nitrogen removal and phosphorus removal performance of polylactic acid-pyrrhotite synergistic denitrification column reactor were investigated,and the initiation time of the membrane hanging of the synergistic reactor was short,and the nitrate nitrogen removal rate reached more than 95% after the 10 th day.The optimal experimental conditions of the co-reactor were HRT=24 h,and the concentrations of nitrate nitrogen and phosphate in the influent water were 40mg/L and 6 mg/L,respectively.Under these conditions,the concentrations of nitrate nitrogen and phosphate in the effluent were 0.82 mg/L and 0.32 mg/L,respectively.The rate of nitrogen and phosphorus removal in the reactor increased with the increase of nitrate nitrogen concentration and phosphate concentration in the influent water,respectively.During the operation of the reactor,the effluent COD is relatively stable and lower than that of the polylactic acid column reactor as a whole,and the acid-base balance in the reactor is conducive to the physiological role of microorganisms;The effluent sulfate concentration showed a decreasing trend,which indicated that polylactic acid and pyrrhotite denitrification could reduce the effluent sulfate concentration.The packing scanning electron microscopy showed that the surface of pyrrhotite was loose and porous before the experiment,which was easy to attach to biofilms and adsorb pollutants such as phosphate.After the experiment,the surface of pyrrhotite was almost covered with biofilm,and the surface of polylactic acid was damaged by bioavailability.3.Through the results of high-throughput sequencing analysis,it can be seen that the microbial community structure of denitrification of polylactic acid of different molecular weights is different.The microbial community structure of the polylactic acid reactor and the polylactic acid-pyrrhotite synergistic reactor are also different.The level composition of the microbial community gate was analyzed,and the main dominant gates of polylactic acid static denitrification experiments and each reactor were Proteobacteria and Chloroflexi.The main dominant families of microbial community polylactic acid static denitrification experiments were Methylophilaceae,Anaerolineaceae and Hyphomicrobiaceae,and the main dominant families in the column reactor were Saprospiraceae,Methylophilaceae and Anaerolineaceae;Microbial communities were analyzed at the subordinate level,and the main dominant genus of polylactic acid static denitrification experiments was Methylotenera,norank＿f＿Anaerolineaceae and Hyphomicrobium,and the main dominant genus of column reactor was Phaeodactylibacter,Methylotenera and Hyphomicrobium.