Effect Of A Strengthened Floating Bed On The Purification Of Urban Landscape Water Supplied With Reclaimed Water

Ecological floating beds are widely used in the restoration of eutrophic landscape water bodies due to their green economy,no additional land occupation,and rich ornamental properties.While landscape water bodies supplied with reclaimed water generally have a low C/N ratio,and insufficient carbon sources limit the water purification effect of ecological floating bed’s impact on the landscape water bodies.Based on this,this study firstly monitored the changes of water quality of actual landscape water bodies supplied with reclaimed water after laying traditional ecological floating beds.Then,an ecological floating bed（EFB）,an enhanced ecological floating bed with suspended plant carbon sources（C-EFB1）,and an enhanced ecological floating bed filled the plant carbon sources（C-EFB2）were set up to explore the purification effect of the simulated landscape water bodies supplied with reclaimed water.In addition,the effect of carbon source addition position on the effect of enhanced denitrification in ecological floating bed was tested.This study can provide guidance for the application of plant carbon sources enhanced ecological floating bed on water quality purification of landscape water bodies supplied with reclaimed water,and provide an effective way for the resource utilization of floating bed plants after harvesting.The main results and conclusions are as follows:1)The monitoring results of the water quality of the actual landscape water bodies with and without the ecological floating bed showed that,compared with the control,the average removal rates of the water turbidity,COD,TN,NH₄⁺-N,NO₃^--N,TP,algae density and Chl-a in water by the ecological floating beds were 6.9%,23.2%,20.85%,24.15%,15.68%,40.24%,35.51%and 28.16%,respectively.Therefore,the ecological floating bed has limited effect on the water purification of the landscape water supplied with reclaimed water.In addition,the monitoring results also showed that the C/N ratio of the landscape water supplied with reclaimed water is low,and the ecological floating bed was not effective in removing NO₃^--N.Therefore,it is necessary to add an additional carbon source to the ecological floating bed to strengthen its purification effect of NO₃^--N in the landscape water bodies supplied with reclaimed water.2)Taking calamus as the plant carbon source,when the moisture content was 58%and the particle size was 8 cm,the COD release rate of the plant carbon source was the slowest as 11.7 mg/d,which was suitable as a slow-release carbon source.The BOD₅/COD value of the leachate from the carbon source of plant was 0.65 after soaked for 72 h,which showed strong biodegradability.At the same time,by measuring the change of DOM content in the leachate before and after denitrification,it was proved that the organic carbon released by the calamus plant carbon source was mostly tyrosine protein substances,which were easily utilized by denitrifying bacteria.3)The introduction of plant carbon source in C-EFB1 and C-EFB2 could improve the water quality of the simulated landscape water supplied with reclaimed water and keep it relatively stable.In the whole experiment,the average removal rate of C-EFB1on TN,NO₃^--N,algae density and Chl-a were 62.24%,92.84%,79.01%,67.87%,and the average removal rate of C-EFB2 on TN,NO₃^--N,algae density and Chl-a were64.24%,92.24%,76.82%,51.41%,respectively.Both C-EFB1 and C-EFB2 could maintain the water quality of landscape water bodies at Grade IV.Different carbon source filling methods had impact on the release rate of carbon sources.In the filling mode,the release rate of carbon sources is slower,but the effect on the removal efficiency of pollutants in water by C-EFB1 and C-EFB2 were not significant（p<0.05）.At the same time,the plant carbon source has not caused secondary pollution to the water body,and the safety is good.4)The addition of plant carbon source could promote the vigorous growth of floating bed plants.At the end of the experiment,the dry weight gain of Celandine and Calamus biomass in the C-EFB1 system was 8.7%and 113%higher than that in the EFB system,respectively.At the same time,the plant carbon source promoted the removal of NO₃^--N from the sediment.After adding the plant carbon source,the microbial community structure in the ecological floating bed system changed greatly,and the microbial demeanor and diversity were greatly improved.Among them,the relative abundance of functional bacteria related to denitrification,such as Proteobacteria,Bacteroidetes,Actinobacteria,Chloroflexi and Firmicutes,was greatly increased.