Development And Research Of Online Monitoring Device For Planktonic Algae Concentration In Water Bodies

In recent years,with the rapid economic development and population growth in China,the country is facing the problem of increasing water scarcity.The widespread use of chemical fertilizers containing nitrogen and phosphorus,as well as the direct discharge of untreated domestic sewage into rivers and oceans,has led to increasing eutrophication of water bodies and very serious damage to the ecological environment of water bodies,resulting in disasters such as water blooms and red tides,which have an increasing negative impact on sustainable economic development.In lakes and oceans,blooms and red tides can occur when a single algal bloom occurs,respectively.The concentration of chlorophyll a can reflect the amount of algae and other phytoplankton in the water body,which can predict the nutrient level and water pollution status of the water body.In this paper,a low energy consumption and high sensitivity online monitoring system for the concentration of phytoplankton in water is developed based on fluorescence analysis.The main work done in this paper is as follows:(1)The traditional detection method of chlorophyll a concentration is introduced,the mechanism and conditions of fluorescence generation and the relationship between fluorescence intensity and solution concentration are elaborated and analyzed,and the factors influencing fluorescence intensity are discussed,and the law of fluorescence intensity variation with chlorophyll a concentration is obtained by using Lambert’s law,and the chlorophyll a content is used to reflect the enrichment degree of planktonic algae in water bodies.(2)The characteristics and defects of the domestic and foreign water planktonic algae concentration detection products were analyzed,and a planktonic algae concentration monitoring system with high sensitivity,low power consumption and no reagents was designed according to the requirements.The system selects a 405 nm near-ultraviolet semiconductor laser as the excitation light source of the system,a silicon photocell with high conversion efficiency and stable performance as the receiver,and a quartz cylindrical lens as the beam expander to extend the diameter of the laser beam,and the fluorescence excitation-acquisition optical path is designed and completed.(3)With Raspberry Pi as the main control program module,the optical path structure and hardware circuit were designed rationally,and the 4G data transmission module was analyzed and introduced.A SQLite database was created,and a cell phone APP was developed based on the Android platform to achieve real-time,online observation of algae content in water.(4)In order to verify the stability and reliability of the system,three sets of experiments were designed and completed.Experiment 1 was conducted by configuring a series of different concentrations of Chlorella solution for data acquisition,and it was found that when the concentration of Chlorella solution is low,the voltage value has a positive linear relationship with the concentration of Chlorella solution,which satisfies Lambert’s law;Experiment 2 was conducted under dark environment and daylight environment for data acquisition of Chlorella solution,and by comparing the results of the two sets of experiments,the fluorescence obtained by the system under daylight background conditions was proved to be The accuracy of the collected values was demonstrated by comparing the results of the two experiments.The stability of the system was verified by comparing the results of the two experiments.