Study On Monitoring Technology Of Phytoplankton Concentration In Water Based On Chlorophyll Fluorescence

In recent years,with the rapid development of China's economy,the shortage of resources is becoming more and more serious,especially the shortage of water resources.A large number of fertilizers containing nitrogen,phosphorus and other chemical elements are widely used.Excessive domestic sewage is directly discharged into the river and sea without treatment,which leads to serious eutrophication of water body.The water bloom and red tide caused by this phenomenon have long-term harm to the sustainable development of economy.Algal blooms and red tides occur in lakes and oceans respectively.The content of chlorophyll-a in water body can reflect the concentration of phytoplankton,so it has become one of the main parameters to evaluate the eutrophication of water quality.In this paper,a low-energy,portable phytoplankton concentration monitoring system is studied to realize online monitoring of phytoplankton concentration based on chlorophyll fluorescence.Firstly,the luminescence mechanism of chlorophyll-a fluorescence and the characteristics of excitation spectrum and emission spectrum of chlorophyll-a are introduced.The measurement principle of fluorescence analysis method is analyzed emphatically.The relationship between fluorescence intensity and chlorophyll-a concentration is obtained by Lambert Beer principle.The concentration of chlorophyll-a reflects the concentration of phytoplankton in water.Secondly,according to the design requirements of low energy consumption,portable and sampling free planktonic algae concentration monitoring system,the system uses dual band led to form excitation light source,sensitive Si PIN photodetector is used as the receiver,high-quality narrow-band filter is selected to reduce the light interference in other bands,and a 90°integrated fluorescence excitation acquisition optical path is designed.Thirdly,the circuit system is designed and developed based on STM32 MCU,including driving power module,excitation light source module,fluorescence value acquisition module,parameter setting module,GPS/Bei Dou dual-mode positioning module,4G data transmission module,fluorescence information storage module,OLED display module.Based on Huawei cloud server,the system built a cloud platform for monitoring phytoplankton concentration in water,established a database based on My SQL,developeda monitoring website based on HTML5,and developed a mobile app based on Android platform,which realized online real-time viewing of algae concentration data on multiple platforms.Finally,the absorption spectrum of chlorophyll was measured by spectrometer,and two groups of experimental verification were completed.In Experiment 1,the excitation light intensity was controlled by changing the current,and the data of different concentrations of chlorophyll ethanol solution were collected.It was found that the accuracy of chlorophyll fluorescence signal acquisition could be effectively improved by properly adjusting the intensity of excitation light source;in Experiment 2,the data acquisition of chlorophyll ethanol solution in dark environment and sunlight environment was compared,which verified the system fluorescence acquisition under the sunlight background.The accuracy and validity of the value.Through repeated experiments,the system has good stability.