Selection Of The Dominant Microalgae Community In Wastewater Treatment And Performance Of Its Nitrogen And Phosphorus Removal

Microalgae is a kind of biomass energy,which can associate nitrogen and phosphorus elements in water to form its cells.Constructing microalgae community system baesd on dominant algae species in receiving water of sewage treatment plant effluents,can improve the efficiency of algae technology in the actual sewage treatment,which has important practical significance.In order to select the dominant algae in the receiving water of sewage treatment plant effluents and construct the microalgae community system,based on the physical and chemical data of algae and water quality in the receiving water of sewage treatment plant from October,2018 to September,2019,the characteristics of phytoplankton community structure in the study area were analyzed;combining the data of field sampling and algae characteristics,the experimental algae species were selected and expanded;under different temperature and nutrition conditions,the growth rate and pollutant removal rate of the algae were compared,and the algae with high growth activity and high nitrogen and phosphorus removal ability were selected;construct different microalgae community systems and compare their nitrogen and phosphorus removal capacity and system stability.Based on the above research,the results are as follows:?1?A total of 49 genera,belonging to 7 phyla were identified,among them,there are 16 genera in diatom,14 genera in Chlorophyta and 12 genera in Cyanophyta.In June,2019,the number of genera is the most,25 species,and in September,2019,the number of genera is the least,11 species.Diatoms and Cyanobacteria dominate the whole year.The density range of phytoplankton cells in the whole year was2.78×10⁵cells/L?2.28×10⁶cells/L.The variation range of H'value in the whole year is4.61-2.72,the variation range of J value is 1.07-0.69,the variation trend of H'value and J value in the whole year is the same,the variation range of D value is 0.88-0.32,the density of dominance in February is higher,the value of D was maximum,and the density of dominance in August is lower,the value was minimum.There was a significant positive correlation between algae cell density and DO value in the study area?P<0.01?,indicating that with the increasing of DO value,the algae cell density in the water body also increased,there was a significant negative correlation with WT?P<0.05?,that is,when the WT increased,the density of algal cells decreased,tt was speculated that the water output is larger in summer,so the density of phytoplankton was diluted in summer.?2?Based on the previous sampling data,growth characteristics,growth activity and research value of algae,Chlorella sp.,Scenedesmus obliquus,Nitzschia sp.,Chlamydomonas reinhardtii and Cyclotella sp.were selected as experimental algae.Through the experiments,the conclusion is as follows:when the temperature was10?,the growth rate and nutrient removal efficiency of Cyclotella sp.and Nitzschia sp.is relatively better,at the end of the experiment,the removal efficiency of TN reached 89.50%and 84.19%,and the removal efficiency of TP reached 94.83%and95.86%;when the temperature was 20?,the cell activity of each algae is stronger,and the growth trend is stable,the nutrient removal efficiency of Cyclotella sp.and Nitzschia sp.was the best,at the end of the experiment,the removal rate of TN was91.20%and 85.25%,and the removal rate of TP was 97.07%and 94.42%;under the condition of low nutrition and general nutrition,most of the algae grow stably,and the nutrient removal efficiency of Scenedesmus obliquus was the best,at the end of the experiment,the removal rate of TN was 93.79%and 84.78%,and the removal rate of TP was 94.75%and 83.89%;under the condition of high nutrition,algal cells began to die,and the removal efficiency of algae was poor,the removal ability of Scenedesmus obliquus was relatively better,the removal rate of TN was 67.27%,the removal rate of TP was only 43.48%.In summary,Scenedesmus obliquus,Nitzschia sp.and Cyclotella sp.all have strong growth activity and better pollutant removal ability under different temperature conditions and different nutrition conditions,so they are selected as the dominant algae species.?3?Community A is composed of Scenedesmus obliquus and Nitzschia sp.,community B is composed of Scenedesmus obliquus and Cyclotella sp.,community C is composed of Nitzschia sp.and Cyclotella sp.,and community D is composed of Scenedesmus obliquus,Nitzschia sp.and Cyclotella sp..When the concentration of TN in the influent was 23.92mg/L,the community C has the best removal effect,the lowest TN concentration in the effluent is 1.48mg/L,and the removal rate is 93.83%;when the concentration of NH₃-N in the influent was 3.55mg/L,the NH₃-N content in the effluent of the community C decreased continuously,the minimum concentration of effluent was only 0.30mg/L,and the removal rate was 91.56%;when the concentration of TP in the influent was 5.84mg/L,the lowest TP concentration in the effluent of community C was 0.26mg/L,and the removal rate was 95.55%.In summary,community C has stronger nutrient removal ability and community D has stronger syetem stability in wastewater treatment.In conclusion,compared with single algae species,microalgae community has better pollutant removal ability and higher wastewater treatment efficiency.There is no positive correlation between community diversity and pollutant removal capacity,but the system stability can be enhanced with the increase of community diversity to a certain extent.It is suggested that different microalgae should be selected for different wastewater,and algae species should be increased to improve community diversity and maintain the stability of microalgae community system.