Factors Analysis And Control Technology Of Algae Bloom In Typical Urban River

The water environmental quality of urban rivers has been dramatically improved in recent years.However,algal bloom was continuously found in some of the urban rivers which was the signal of the city's environmental quality.As a result,the algal bloom would have a lot of negative impacts on the society.As a typical urban river,the T River was selected in thesis to investigate on the mechanism and targeted prevention treatments of the algal blooms.In the thesis,the algal species,water quality,meteorological factors,etc.were monitored and analyzed to find the key factors that controlled the algal blooms and to propose the targeted prevention treatments.By monitoring algae population,it could be found that the phyla and genera of the algae in the river are 7 and 9 respectively.And the primary species of alga in the river vary from diatom-blue green alga to diatom-din flagellate-cryptomonas,changing into green alga-cryptomonas-diatom finally.The water bloom is mainly caused by blue-green alga.The dominant species of alga in the river is microcystis aeruginosa.In fact,the alga amount in each monitoring site is larger than 10×105 by volume,however smaller than 10×106 by volume,which is in accordance with the phenomenon that there were a small number of algae and didn't form into water bloom in initial experiment stage.Each water quality parameter is as following:the average water temperature is above 20 ? in early stage,while 15 ? in late period;the alkalinity is above 7.6,which presented a weak alkaline environment;the dissolved oxygen distributed with a fluctuation range from 4.5 to 6.6 mg/L;the average ammonia concentration is 0.15 mg/L;total phosphorus fluctuated in the range from 0.085 to 0.115 mg/L,which exceeded water bloom critical value;the permanganate index is in the range of 2-2.27 mg/L;the content of chlorophyll A is below 10 mg/m3;the Concentration ratio of nitrogen and phosphorus changed from 5 to 60.It could be concluded that the temperature,total phosphorus,and n/p ratio are the main factors leading to water bloom.The average water temperature is 20 ? no more than 25 ?,which is beneficial to the boom of algae;in the meantime,the wind speed is slight,which is suitable for aggregation of alga;as a result,the wind direction,rainfall,and air pressure has a promotion or inhibition effect on the grow of alga.In order to prevent and control water bloom,such measures as quality early warning monitoring,water quality factors prevention and control,and ecological management were put forward according to the main factors caused water bloom.Moreover,this paper also conducted experiments aim at inhibiting microcystis aeruginosa with inhibitors such as hydrogen peroxide,chitosan-modified clays,barley straw,and so on.The concentration of hydrogen peroxide used in the experiment was 25,50,75,and 100 mg/L.The concentration of chitosan-modified clays used in the experiment was 5,10,20,and 50 mg/L.The concentration of barley straw used in the experiment was 1.0,2.0,4.0,and 8.0 g/L.All these inhibitors have a good effect on inhibiting or removing alga.And the optimal concentration of hydrogen peroxide,chitosan-modified clays,and barley straw are 50mg/L,10 mg/L,and 8 g/L.