Study On The Removal Effect Of Chlorella Pyrenoidosa On Nitrogen,phosphorus And Organic Matter In Domestic Sewage

Compared with the traditional sewage treatment process,using algae to treat wastewater can realize the recovery of nitrogen,phosphorus and other resources with high efficiency and low consumption method,which is worth further study.The research on the removal effect of algae on nitrogen,phosphorus and organic matter in wastewater is relatively extensive,however,there are few studies on the removal of organic matter with different characters by algal.In addition,more alternative bacteria strains need to be developed for the treatment of wastewater by the the consortium of microalgae and bacteria.In this study,an analysis of the removal effect of Chlorella pyrenoidosa with different cultivation methods on pollutants such as nitrogen,phosphorus and organic matter in wastewater was carried out.Besides,in continuous culture system,the removal of organic matter with different characters?molecular weight and fluorescence characteristics?by algal cells was studied and the analysis of its microbial community structure and the prediction of function of the dominant bacteria were carried out.It provided some theoretical support for the study of wastewater treatment by algae,the removal effect of algae to organic matter with different characteristics and the screening of bacteria in the consortium of microalgae and bacteria.The results showed that:?1?The experiment on the treatment of wastewater by Chlorella pyrenoidosa with batch cultivation showed that,the best reaction time of removal of total organic carbon?TOC?was 3-8 d,but the content of nitrogen and phosphorus decreased continuously with the increase of reaction time and the descent rate slowed down around the 8th day.Therefore,based on the analysis of algal cell growth and pollutant removal efficiency,the optimal reaction time range of Chlorella pyrenoidosa for wastewater treatment was3-8 days.?2?Three HRT gradients of continuous system were drafted based on the experimental study of algae cultured through batch cultivation:7.5 days,4.5 days and3 days.The effect of different HRT gradients on the removal of pollutants under the condition of continuous inflow and outflow was studied.The results showed that different HRT gradients had no significant effect on TOC removal,and the removal rate can reach about 90%.However,the removal efficiency of nitrogen and phosphorus pollutants increased with the increase of HRT.?3?The ultrafiltration and three-dimensional fluorescence spectrum?3D-EEM?were used to analyze the removal effect of Chlorella pyrenoidosa on organic matter with different characteristics,the results showed that,the removal effect on low and medium molecular weight organics?<1k Da,1?3k Da,3?5k Da?was better and the removal rate was between 80%-95%.The removal efficiency of organics with molecular weight of less than 1k Da and between1-3k Da decreased with the increase of HRT,and the removal efficiency of organics with molecular weight of 3-5k Da increased with the increase of HRT.According to the results of FRI and PARAFAC of 3D-EEM,the removal of tryptophan by algal cells was better than others.Combined with the results of UV₂₅₄,SUVA and parameters of fluorescence,during the operation of the reaction system,microbial products such as algae organics might have an impact on the removal efficiency of organic matter.?4?High-throughput 16S rDNA sequencing technology was used to analyze the microbial community structure of the continuous reaction system in different operation stages.The results showed that the Shannon index of microorganisms in each reaction system was 1.76?3.22,and the diversity of microorganisms in the system was generally high and gradually increased with the increase of system operating time,which had no significant relationship with different HRT gradients.21 bacteria phylums and 48bacteria genus were detected in all samples.Cluster tree and PCA?Principal Component Analysis?at genus level showed that the dominant bacteria changed greatly with the advance of operation time.The abundance distribution of functional genes based on KEGG?Kyoto Encyclopedia of Genes and Genomes?database and the application and discovery of dominant bacteria in related research indicated that,bacteria infected in each reaction system might promote the purification of wastewater to a certain extent,such as Pseudomonas and Acinetobacter,this kind of endophytic dominant bacteria symbiotic with algae,which had effects on water purification and could adapt to the growth environment of wastewater treatment system well,can be used as the bacterial alternative for the the consortium of microalgae and bacteria.The results showed that batch and continuous cultivation of Chlorella pyrenoidosa had a good effect on the removal of nitrogen and phosphorus and organic matter,and HRT had a greater effect on the removal of nitrogen and phosphorus.The removal effect on organics with low and medium molecular weight and tryptophan protein organics was good.In continuous reaction system,the species of endophytic bacteria was abundant,dominant bacteria such as Pseudomonas and Acinetobacter,which might have effects of water purification and could adapt to the growth environment of wastewater treatment system well,can be used as the bacterial alternative for the consortium of microalgae and bacteria.The results above could provide theoretical support for the study about the removal of organics with different characters and the screening of bacteria in the consortium of microalgae and bacteria,which could promote the utilization of algae for wastewater resources.