Study And Application Of Seawater BOD Fluorescence In-situ Sensor

Biological oxygen demand(BOD)can be defined as the amount of dissolved oxygen consumed in the process of decomposition of organic matter in water by aerobic microorganisms into inorganic substances.This index indirectly reflects the amount of organic pollutants in water,which is an important indicator of the degree of water pollution.In China's national environmental protection standard HJ505-2009,the method of dilution and inoculation for the measurement of BOD in water is stipulated.This method requires 5 days to measure BOD.The measurement cycle is too long to reflect the pollution status of organic matters in water timely and efficiently,and it cannot be applied in the case that the content of organic pollutants in water needs to be measured quickly.Therefore,it is necessary to develop a sensor that can monitor BOD in real time on site.According to the above research,this paper explores the possibility of detecting the seawater BOD by the seawater BOD fluorescence in-situ sensor based on fluorescence analysis.The excitation of the tryptophan in water through the ultraviolet band could generate fluorescence,which is basic measuring principle of the sensor.The detector detects the fluorescence signal and converts the tryptophan fluorescence signal into the related biochemical oxygen demand by the built-in correction parameters of the sensor.The BOD is indirectly measured by tryptophan,and the problem of real-time monitoring of BOD is solved.Compared with the dilution and inoculation method mentioned in the national environmental protection standard which needs to collect water samples back to the laboratory and take 5 days to get the final result,this sensor can detect BOD in real time,without taking samples back to the laboratory,and does not need to add any chemical substances into the water.Therefore,there is no pollution to the environment,and it has the advantages of fast,simple,portable,stable performance and so on.It has strong applicability in some occasions where the BOD detection accuracy is not too high and real-time and stable measurement are required.The seawater BOD fluorescence in-situ sensor based on STM32 MCU of ARM Cortex M3 to achieve the modulation of the light source.The photomultiplier PMT was used to detect the tryptophan fluorescence signal,which was converted into a voltage signal.The signal was collected by the ADC and sent to STM32 MCU for data processing.The obtained BOD value was transmitted to the upper computer for display.In the aspect of optical path structure,the excitation light path is perpendicular to the detection optical path to reduce the interference of the excitation light on the detected fluorescent signal.The main content of this paper is the development of the hardware circuit design and software part of BOD fluorescence in-situ sensor.The hardware circuit part mainly includes the design of the LED driving circuit,the data acquisition control circuit,the data acquisition circuit,and the interface level conversion circuit.The software part mainly deals with the configuration of the microcontroller and the processing of the data.Finally,the development of seawater BOD fluorescence in-situ sensor was completed by combining experimental test and seawater field test.Compared with other traditional sensors for measuring BOD,the measurement mechanism adopted by the BOD fluorescence in-situ sensor is relatively novel,and the linearity of the sensor measurement results is better.And the sensor has certain stability,reliability,good portability,and certain practical value.