Study On The Effect Of Pre-Aeration And Elastic Filler On Nitrogen And Phosphorus Removal In Duckweed Ecological Pond And Its Mechanism

Duckweed,as a small floating aquatic macrophyte with wide distribution around the world,can rapidly grow in the polluted water bodies and form a duckweed-based ecological pond system（DP）.Based on the fact that growing duckweed can absorb water pollutants such as nitrogen and phosphorus and produce duckweed biomass containing high contents of protein,starch and medicinal ingredients,DP can be used for sewage treatment and simultaneously achieve multiple goals including water purification,biomass production and resource utilization of carbon,nitrogen and phosphorus.In addition,the DP also has many other advantages such as low construction cost,low energy consumption and easy management,which makes it attract great attention in recent years.However,as a result of low dissolved oxygen（DO）and a small amount of microbial film and functional microorganisms in the water body,DP also has some shortcomings,such as low pollutant removal rate and large demand of land,which greatly limits the popularization and application of this technology.In view of this,this study aims to conduct single enhancing technology（pre-aeration）and combined enhancing technology（pre-aeration +artificial filler）in a outdoor pilot-scale DP（2 h of aeration durations,the artificial filler is strip-shaped artificial filler）;to explore the impact of related enhancing technologies on pollutant removal and the application potential in a DP;to investigate the effects of the enhancing technologies on the microbial community of the DP by using the high throughput sequencing;and then to reveal the microbial mechanism of pollutant removal promoted by the enhancing technologies.The result shows:（1）The single enhancing technology of pre-aeration not only significantly increased the DO and ORP of the DP with an increasing rate of 478.26% and54.62%,respectively),but also significantly increased the dry weight growth rate of duckweed and the recovery rates of nitrogen and phosphorus with an increasing rate of 32.87%,27.03% and 13.16%,respectively.However,it has no significant effect on the contents of nitrogen and phosphorus in duckweed.In addition,pre-aeration can also significantly promote the removal of TP,TN,ammonia nitrogen and turbidity in the DP with an increasing rate of 84.06%,79.69%,85.50% and 28.78%,respectively.Although pre-aeration can simultaneously promote the removal of nitrogen and phosphorus by affecting the action of duckweed and microorganisms,the promoting effect through the action of microorganisms is greater.Bacterial community analysis shows that pre-aeration can increase the relative abundances of plant growth-promoting bacteria（such as Flavobacterium）,denitrifying bacteria（such as Pseudomonas,Sphingomonas）and phosphorus-accumulating bacteria（such as Acinetobacter）in the DP as a result of increasing DO in the pond water,which may be the main reason why pre-aeration can promote the growth of duckweed and the removal of pollutants in the DP.（2）The combined enhancing technology of pre-aeration and artificial filler not only significantly increased the DO and ORP of the DP with an increasing rate of 243.23% and 37.06%,respectively,but also significantly increased the duckweed dry weight growth rate and the recovery rates of nitrogen and phosphorus with an increasing rate of 31.09%,0.49% and 41.67%,respectively.In addition,the combined enhancing technology significantly promoted the removal of TP,TN,ammonia nitrogen,and turbidity in the DP with an increasing rate of 80.14%,98.10%,84.84% and 31.48%,respectively.Bacterial community analysis showed that the high microbial contribution rate of nitrogen removal in the DP may be a result of the large number of microbial membranes and functional bacteria enriched on the surface of the filler.Meanwhile,the combined enhancing technology can also increase the relative abundances of plant growth-promoting bacteria（such as Flavobacterium）,denitrifying bacteria（such as Pseudomonas）and phosphorus-accumulating bacteria（such as Acinetobacter）in the DP,which may be the reason why the combined enhancing technology can promote the growth of duckweed and the removal of pollutants in the DP.It is worth noting that the dominant bacteria are significantly different between the DP with single enhancing technology and combined enhancing technology,indicating that the presence of artificial fillers also has an important impact on the bacterial community of the DP.This study confirmed that both the single enhancing technology（pre-aeration）and the combined enhancing technology of pre-aeration +artificial filler)can significantly improve duckweed growth and pollutant removal in the pilot-scale DP,and also revealed the main reason and mechanism of pollutant removal promoted by the two enhancing technologies in the DP.It can be concluded that although two enhancing technologies can simultaneously improve the action of duckweed and microorganisms to promote the removal of nitrogen and phosphorus,the promoting effect of microorganisms is greater.Compared with the single enhancing technology,the combined enhancing technology performs better in terms of the comprehensive effect.The results can provide guiding measures and scientific basis for the improvement of duckweed growth and pollutant removal in the DP,and have certain theoretical and practical reference values for the large-scale application of the DP.