Effect Of Carbon Sources And COD/ρ(TN)ratio On SMP Content And Microbial Community Structure Of Denitrifying Biological Filter

Generally,the content of organic matter in the secondary wastewater of municipal sewage treatment plants is relatively low,which cannot meet the needs of electron donors for deep denitrification under anoxic conditions.To solve this problem,feeding external organic carbon is a common method in practical engineering.Denitrifying biological filter（DNBF）is generally viewed to be an effective,economical,stable technology and often applied to advanced nitrogen removal both here and abroad.After DNBF advanced treatment,urban secondary effluent can effectively relieve the pressure of water resources in China.During biochemical treatment,denitrifying microorganisms have different carbon source metabolism pathways,which release a kind of organic mixture to the surrounding environment when using carbon source,namely soluble microbial product（SMP）.The characteristics of organic carbon sources have a great effect on the metabolic pathways of microorganisms.Thus,the type of carbon source and the ratio of COD/ρ（TN）would influence the function of microbial metabolism,resulting in the variety of nitrogen removal effect,content of SMP and its components,micbobial community structure.Based on the chemical composition analysis,fluorescence excitation-emission matrix（EEM）combined with parallel factor analysis（PARAFAC）,high throughput sequencing,FTIR spectroscopy,this thesis was focused on the treatment performance,content and components of SMP,microbial community in the lab-scale DNBF reactor fed with carbon sources of sodium acetate and glucose under the different COD/ρ（TN）conditions,and the optimal ratio of COD/ρ（TN）ratio was obtained.In addition,considering high content of SMP,the difficulty of maintaining p H stability of sodium acetate system,the problem of slow denitrification rate and large carbon source consumption in glucose system.Therefore,on the basis of the optimal COD/ρ（TN）ratio of sodium acetate and glucose,this thesis further explored the influence of the mixed carbon source of sodium acetate and glucose（COD/ρ（TN）=6.5）on the effluent water quality,content of SMP and its components,and microbial community structure of DNBF,and the best carbon source was selected.The main research contents and results were as follows:（1）The denitrification biological filter could be quickly started within 12 days when sodium acetate was used as the electron donor.The TN concentration in effluent was below2.0 mg/L and the accumulation of NO₂^--N was small.The analysis of pollutants along the course showed that the filter column had an efficient section with 0～25 cm along the flow direction,and more than 79%of the pollutants were removed in this section because of the sufficient organic matter.（2）When the carbon source was sodium acetate,and COD/ρ（TN）ratio was respectively 3.5,5 and 6,TN removal rate and effluent SMP content increased with the increase of COD/ρ（TN）ratios,the content of polysaccharide in SMP was always higher than that of protein.The tryptophan component in SMP was the lowest at COD/ρ（TN）ratio of 5.In addition,the composition and diversity of microbial communities corresponding to different COD/ρ（TN）ratios from high to low was 5,6 and 3.5,respectively.And the proportion of Proteobacteria which made contribution to the degradation of organic matter and SMP was the highest at COD/ρ（TN）ratio of 5.Therefore,when the sustrate was sodium acetate,the optimal ratio of COD/ρ（TN）was 5.（3）When the carbon source was glucose,and COD/ρ（TN）was respectively 6,8 and 10,the denitrification performance was associated with COD/ρ（TN）ratios.When the COD/ρ（TN）reached to 8,the removal rate of COD would not be changed with COD/ρ（TN）ratios increased,and nitrogen removal rate was above 85%.SMP content increased with the increase of COD/ρ（TN）ratios.Tyrosine and humus components in SMP increased with the increase in COD/ρ（TN）ratios the amoeba（Proteobacteria）is the dominant flora in the system,and its relative abundance from high to low was 8,6 and 10.Considering the denitrification effect,content of SMP and economic cost,the optimum COD/ρ（TN）was 8.（4）Compared to the single carbon source of sodium acetate and glucose,the dosing cost of mixed carbon source was the lowest,amd their mixture was advantageous over single carbon source in less SMP production and more abundant in microbial community diversity,meanwhile the treatment performance no less than the sodium acetate system.Different carbon sources had a significant effect on the evolution of SMP components.The intensity of fluorescence component was component 1（tyrosine protein）>component2（tryptophan protein）>component 3（humus like substance）,the tyrosine and tryptophan protein-like components in SMP were the lowest in the mixed carbon source system.Microbial communities were abundant in the mixed carbon source system.Therfore,considering the denitrification effect,SMP yield,microbial diversity and economic cost comprehensively,the mixed carbon source has more advantages and could be used as an alternative carbon source for DNBF system.