Filamentous Green Algae Bloom In Aquatic Environment With Submerged Macrophytes And The Inhibition Efficiency Of Green Algae By Nanocomposites Cu@C/Carriers

After decades of efforts to prevent and control water pollution,severely polluted water bodies have been reducing year by year in China’s urban areas,and the surface water quality has been steadily improved.In the process of promoting continuous improvement of urban water environment,the problem of low-load pollution has been emerging recently.Reconstruction of submerged macrophytes is an important means of remediating slightly polluted water bodies,but this process is often accompanied by the issue of filamentous algae proliferation.In this study,the main factors affecting the breeding of filamentous green algae in aquatic environment with submerged macrophytes were investigated through periodic monitoring of filamentous algae growth and water environmental indicators in two representative water bodies.In response to filamentous algae bloom,traditional chemical methods often cause serious damage to other aquatic creatures in the process of killing algae,which poses great eco-environmental risks.Therefore,in this study,nanoparticle Cu@C,an algal inhibiting agent,was immobilized onto some engineering materials commonly used in practical water treatment to make a series of nanocomplex Cu@C/carriers.In addition,the inhibition effect and the ecological risk of applying these nanocomplexs were assessed.The aim of this study is to optimize the control of filamentous algal bloom in aquatic environment with submerged macrophytes.Main conclusions were as follows:（1）The filamentous algaes in Qingpu（QP）and Gaodong（GD）were dominated by Cladophora and Spirogyla.In time distribution,there were more filamentous algaes in summer and autumn,less in spring and winter.The biomass of filamentous algaes reached the peak in autumn.In spatial distribution,there were more filamentous algaes in the monitoring sites with plenty submerged macrophytes.The peak biomass of filamentous algaes reached 720.94 g/m~3 and 188.31 g/m~3 for QP and GD,respectively.The results of random forest analysis and RDA showed that the main factors affecting the breeding of filamentous green algae were NH₄⁺-N（positive correlation）and zooplankton density（positive correlation）in QP,and p H（positive correlation）and zooplankton diversity index（positive correlation）in GD.（2）The results of the immobilization experiments showed that the optimal preparation conditions for PETAQUA,PUSNG and PPNWF were 100 mg/L CCCSNs with 1.5%silane coupling agent KH560,100 mg/L CCCSNs with 1.0%titanate coupling agent CS171,and 100 mg/L CCCSNs with 1.5%silane coupling agent KH570,respectively.The load densities after disturbance were 0.010 g/cm~3,0.076 g/cm~3,and0.014 g/cm~3,respectively.The load stability can reach 85.05%,81.42%,and 76.53%,respectively.The characterization results showed that the immobilization of CCCSNs onto PETAQUA was mainly through hydrogen bonding,while that onto PUSNG and PPNWF was mainly through coupling.（3）The results of filamentous green algae inhibition experiments showed that the physiological status of Spirogyra（a typical filamentous green algae）deteriorated with the increase of the concentration of CCCSNs contained in the four nanoparticles（unfixed CCCSNs,nanocomplex PETAQUA,nanocomplex PUSNG,nanocomplex PPNWF）,which exhibited a trend of low concentration induction and high concentration inhibition.The inhibition effect of each complex on Spirogyra was significantly better than that of unfixed CCCSNs.The optimal IR of PETAQUA,PUSNG and PPNWF was 39.67%,39.55%and 39.27%higher than that of unfixed CCCSNs,respectively.Under high concentration of the four nanoparticles,Chl.a decreased,SP decreased,EC increased,CAT and POD decreased,SOD increased.The optimal inhibitory concentrations of the four nanoparticles（according to the concentration of CCCSNs contained in the complex）were 40 ppm,50 ppm,60 ppm and 60 ppm,respectively.The correlation analysis showed that the four nanoparticles were correlated with IR,EC and MDA（p<0.01）,positively,and correlated with CAT and POD（p<0.01）,negatively.The three complexes were positively correlated with SOD（p<0.01）and negatively correlated with SP（p<0.01）.PETAQUA complex was negatively correlated with Chl.a（p<0.05）,and the other two complexes were negatively correlated with Chl.a（p<0.01）.As to the inhibition mechanism,CCCSNs still played a leading role in the complexes,mainly through inducing oxidative damage of algal cells.（4）The results of eco-environmental risk experiments showed that the concentrations of TN,TP,COD_Mn and Cu²⁺as well as the acute toxicity of luminescent bacteria increased with the increase of CCCSNs concentration contained in the four nanoparticles,presenting an overall upward trend of“slow-sharp-slow”.The concentrations of Cu²⁺dissolved by the four nanoparticles were far below the national standard.In general,the biological toxicity order was unfixed CCCSNs>nanocomplex PETAQUA>nanocomplex PPNWF>nanocomplex PUSNG.Nanocomplex PUSNG was considered to enjoy the greatest potential for engineering.