Investigation Of Landscape Water In Xi'an And Basic Research On Algae Removal

In this study,water quality and ecological indicators of four typical landscape water bodies in Xi'an City were investigated regularly,and the variation rules of water quality,algae and zooplankton under different recharge sources were analyzed.Then the eutrophication degree of each water body was evaluated by different index systems,and the applicability and limitations of different evaluation methods were compared and analyzed.Finally,aiming at the blooms caused by the proliferation of Microcystis aeruginosa in the reclaimed water recharge area of the moat in summer,the feasibility of controlling algae outbreaks in landscape waters with aluminium salts was explored,and the algae floating in the process of using aluminium salts for algae removal was explored and analyzed.The main conclusions are as follows:?1?Among the four typical landscape waters,the water body replenished with reclaimed water is high in nitrogen?N?,phosphorus?P?and COD compared with other water bodies,which is more likely to lead to eutrophication and resulted in the increase of algae density,chlorophyll a concentration and turbidity.Moreover,nitrate is the main form of nitrogen in all the water bodies,which could account for more than 50%of TN.?2?Phosphorus concentration had significant positive correlations with chlorophyll a concentration and zooplankton biomass.Phosphorus was the main limiting factor for water eutrophication and algae proliferation.Phytoplankton,such as cladocera and rotifers,had significant correlation with chlorophyll a,while some carnivorous copepods had no significant correlation with chlorophyll a.?3?Thirty-three species of zooplankton were detected in the investigated waters,with the moat being the most abundant,followed by Taohuatan Lake,Fengqing Lake and Xingqing Lake.Rotifers were the most abundant zooplankton species,accounting for more than 70%of the zooplankton,while the species and quantity of phytoplankton in the four typical landscape waters were far less than the corresponding indicators of the natural waters.?4?Eutrophication degree of four landscape waters was evaluated by species diversity index,richness index,evenness index,E/O index,zooplankton number and chlorophyll a concentration.The results showed that the results obtained by chlorophyll a concentration evaluation method were most consistent with the sensory indicators of water body,and the trend obtained by E/O index method was similar to the method using chlorophyll a concentration evaluation while other methods acquired quite different evaluation results.?5?When aluminium chloride and aluminium sulfate were selected to remove algae and phosphorus from water,the removal efficiency of both had little difference under the same dosage.However the removal effect of aluminium chloride on chlorophyll a concentration was better than that of aluminium sulfate when the dosage was low,and the removal effect of aluminium chloride on total phosphorus in water was better than that of aluminium sulfate when the initial concentration of TP in water was low.In addition,the removal of turbidity,TP and chlorophyll a in water can be achieved when the dosage of aluminium salt was 10.0 mg/L.Algae removal by aluminium salts mainly depended on the precipitation of Al³⁺and the net scavenging and trapping of colloids.?6?When the algae were removed by coagulation with aluminium salts,the algae flocs would float up,which affects algae removal efficiency.The floating cause of algae flocs directly lay in producing oxygen of algae photosynthesis,which held the flocs up to the surface of water again.The rate and severity of the flocs floating were related positively with the illumination intensity,the illumination time and the dissolved oxygen concentration.