Eutrophieation And Phytoplankton Growth Investigation,Mechanism Analysis And Ultrasonic Control Of Algae In Xiamen Suburban Watersheds

With the acceleration of urbanization,pollution problems in city suburban watersheds have become more serious.However,many city suburban watersheds have not been investigated,the ecological status is not clear,and there is no scientific basis for formulating plans for governance or improvement of water quality.Based on the eco-environmental survey method,this study conducted an investigation of the eutrophication of three suburban watersheds in Xiamen,and explored the growth factors of dominant phytoplankton,especially the impact of reclaimed water on the growth of dominant phytoplankton,and finally explored the effect of ultrasonic control algae on phytoplankton in suburban watersheds.The aim of this study is to provide a theoretical basis for the ecological evaluation and water environment monitoring of this type for suburban watersheds,and to provide reference for the restoration and sustainable use of such rivers.The main research contents and results of this study are as follows:(1)Taking the three suburban watersheds of Xiamen as the research objects,the ecological environmental investigation was carried out to investigate the water qualities and the influencing factors of phytoplankton biomass,and the eutrophication degree of the watersheds was evaluated by the dominant phytoplankton species.The results showed that the water qualities of the Lianxi reach was the best among these three watersheds,the values of pH met the Class III standard,the values of DO met the Class II standard,the values of COD met the Class V standard,and the values of TP and NH4+-N basically met the Class V standard;However,the pollution of the Houtianyang reach and the 324 national road bypass reach is more serious,and the water quality is worse.Although their values of pH and DO met the Class V standard,most of the concentrations of TP and NH4+-N exceed the Class V standard,even more than 10 times of the Class V standard limits.And the values of COD in the Houtianyang reach fluctuated above and below the Class V standard,except for the October 11th;and only the values of COD in the 2 points of the end of 324 national road bypass reach basically met the Class V standard.The phytoplankton biomass at the beginning and the end of three reaches was kept within 4×105 cells/mL,which was related to rainfall,water te1perature,the value of TP and NH4+-N,water flow and self-purification.The eutrophication degree of three reaches was evaluated by phytoplankton characterization.It was found that the three reaches were dominated by Microcystis and Scenedesmus,so the three reaches were eutrophicated.(2)Taking the dominant algae species,Microcystis aeruginosa,which is common in the genus Microcystis,as the research object.The effects of different nitrogen-phosphorus ratios and WWTP effluent conditions on the growth of Microcystis aeruginosa were researched.The results showed that the cells of Microcystis aeruginosa grew best under the suitable nitrogen-phosphorus ratio(N:P=16:1).When the concentrations of nitrogen and phosphorus were at a low level(P=0.2 mg/L),the higher the concentrations of nitrogen,the longer the growth period of Microcystis aeruginosa cells can reach a higher biomass level.When the concentrations of nitrogen and phosphorus were at a high level(P=1.0 mg/L),the higher the concentrations of nitrogen,the faster the growth rate of Microcystis aeruginosa cells in the growth phase.Under the condition of WWTP effluent of low level nutrient,Microcystis aeruginosa could still grow to a larger biomass level,even algal bloom level,Nmax was 13.46×106 cells/mL.The TP and NH4'-N nutrients in the WWTP effluent played an important role in the growth and reproduction of Microcystis aeruginosa.During the culture,the absorption rate of TP and NH4'-N nutrients was high,reaching 78.87%and 90.63%respectively.(3)Based on ultrasonic conditions:ultrasonic power was 200 W at 4?,working time was 60 s,interval was 5 s,and crushing was 10 times.the ultrasonic experiment was carried out on the water samples of three city suburban watersheds.The results showed that the ultrasonic conditions had good cell disruption ability for the phytoplankton in the three city suburban watersheds,and the breaking rate was above 50%.Among them,this condition had strong cell breaking ability for Cyanobacteria,including Microcystis,Chlorella and so on,the breaking rate is above 50%,and has a high cells disruption.After the phytoplankton cells were broken,the effluent of the cell contents increased the concentrations of nitrogen and phosphorus in the water.However,due to the low biomass of phytoplankton in the water samples,the concentrations of nitrogen and phosphorus did not increase much.