Study On The Abundance Control And Influencing Factors Of Polyphosphate Accumulating Organisms-Tetrasphaera

Tetrasphaera is a new type of polyphosphate accumulating organisms（PAOs）that have only recently been identified.Compared with the traditionally recognized Candidaus Accumulibacer,Tetrasphaera can use macromolecular organic matter such as amino acids and polysaccharides in sewage for anaerobic phosphorus metabolism and fermentation to produce acetic acid and other substances,which has attracted greater interest of Tetrasphaera.In terms of the biological treatment mechanism,high bacterial abundance is the foundation for the effective performance of biological phosphorus removal.However,the factors and control conditions that affect the relative abundance of Tetrasphaera are still unclear.Moreover,given Tetrasphaera’s ability to utilize large molecular weight organic carbon sources,it seems to strengthen the enhanced biological phosphorus removal（EBPR）process’s ability to withstand fluctuations,particularly in terms of competing carbon sources（such as in the presence of NO₃^-）.This study aimed to enrich the dominant community environment of Tetrasphaera and explore its ability to resist NO₃^-interference,factors that control its abundance,and its actual phosphorus removal stability and capacity.Firstly,based on the dominant environment of Tetrasphaera,the present study investigated the influence of NO₃^-on anaerobic phosphorus release metabolism of Tetrasphaera under different carbon source compositions and concentrations.The results demonstrated that NO₃^-has different impact mechanisms on anaerobic phosphorus release of Tetrasphaera under different carbon source conditions.When sodium acetate was used as the carbon source,competition for carbon source between denitrifying bacteria and Tetrasphaera resulted in insufficient carbon source during the later anaerobic phase,leading to denitrification and phosphorus uptake by Tetrasphaera and a subsequent decrease in anaerobic phosphorus release.Meanwhile,when Tetrasphaera was fermenting amino acids anaerobically,NO₃^-disrupted the strict anaerobic environment and inhibited anaerobic phosphorus release of Tetrasphaera even in the presence of sufficient carbon source.However,when serine and sodium acetate coexisted,the increase in substrate accelerated the denitrification rate of denitrifying bacteria per cell,which alleviated the effect of NO₃^-on Tetrasphaera’s anaerobic fermentation of amino acids.Moreover,the abundant carbon source prevented denitrification and phosphorus uptake by Tetrasphaera,leading to a reduction in the impact of NO₃^-on anaerobic phosphorus release of Tetrasphaera and enhancing its ability to resist NO₃^-fluctuations.Secondly,based on the sludge environment dominated by Tetrasphaera as the main PAOs,the study also investigated the effects of different carbon source types（peptone/VFAs）,temperature,and HRT ratio on community structure and phosphorus removal efficiency.Results showed that although phosphorus removal efficiency can reach 89.19%and 86.65%under different carbon source types,the environment with large molecule carbon sources provided a competitive advantage to Tetrasphaera compared to the glycogen accumulating organisms（GAOs）such as Candidatus＿Competibacter.In addition,within the range of23°C to 28°C,Tetrasphaera can maintain high phosphorus removal efficiency（82.67%to 91.54%）and relative abundance（2.50%to 7.98%）,and higher temperature did not decrease its abundance or competitive advantage over GAOs（Candidatus Accumulibacter decreased by 30%when the temperature increased from 20°C to25°C）,indicating that the presence of Tetrasphaera reduces the impact of temperature changes on phosphorus removal efficiency.Moreover,different anaerobic/anoxic HRTs had an impact on the abundance of Tetrasphaera.As an anaerobic fermentation bacterium,Tetrasphaera requires a longer anaerobic time compared to Candidatus Accumulibacter.When the A/O ratio was 1/1.5 to 1/2 and the anaerobic HRT was 1 to2 hours,the system achieved the highest phosphorus removal efficiency（87.30%and87.43%）,which is beneficial for the growth of Tetrasphaera.Lastly,based on the results of the small-scale experimental conclusion,the sludge,already enriched with Tetrasphaera was inoculated in an A²/O small-scale reactor to explore the stability and capacity of Tetrasphaera and denitrifying bacteria acting simultaneously on the removal of pollutants in the system.The results showed that when the device was operated according to the ratio of V_an:V_ax:V_ao=2:3:4,with COD>300 mg/L,TN=60 mg N/L,and TP=5 mg P/L,the effluent concentration of each pollutant in the system met the Class A discharge standard in the Emission Standards of Pollutants for Municipal Wastewater Treatment Plants.Among them,Tetrasphaera,as the main advantage of PAOs in the A²/O system（with a relative abundance of0.32%～1.96%）,even when the influent VFAs were less than 60 mg/L and no external carbon source was added,the system’s denitrification and phosphorus removal effects could be maintained and strengthened.