Research On Shipborne Automatic Monitor For Total Phosphorus And Total Nitrogen In Seawater

The quality status of marine environment will to be understood and masteredefficiently through the development of monitoring technology for TP and TN in seawater.Development of monitoring technology for TP and TN in seawater has laid the foundationfor Environmental Protection. At present, the commercial analyzers for TP and TN athome and abroad are not suitable for seawater monitoring. The research on shipborneautomatic monitor for total phosphorus and total nitrogen in seawater has an increasinglyimportant significance.The online automatic monitoring device for TP and TN in seawater is researched anddeveloped independently in the subject. The device is composed by the digestion module,the color reaction module, the spectrophotometry module and the electronic controlmodule. Various forms of phosphorus and nitrogen in seawater can be digested at a timeby digestion technology including microwave heating chemical oxidation and UVcatalytic photochemical oxidation. Various forms of phosphorus in seawater will invertinto orthophosphate, through the molybdenum blue spectrophotometry to determine.Various forms of nitrogen in seawater will invert into nitrate, through the copper andcadmium restore-spectrophotometry to determine. TP and TN in seawater will be digestedin the same digestion vessel. Coloration and measurement process will be completedrespectively in two different flow paths.Siemens Programmable Logic Controller （PLC） is adopted as core controller of theon-line monitoring device to control the entire monitoring process. The RS232serialcommunication port is configured to communicate with the PLC. The development anddesign of on-line monitoring system software are based on Microsoft Visual C++6.0software development platform. The software is consisted of five parts which are designprocedure module, manual experiment module, real-time monitoring module, parameterconfiguration module and serial communication module. Procedures of digestion,coloration, determination and data processing will be completed automatically under thecontrol of the program of monitoring device through module integration and softwaredesign.The operating conditions of online automatic monitoring device for TP and TN inseawater are explored. The suction time of two flow paths, the speed of peristaltic pump,the collecting time of absorption and the points of acquisition are changed to get stable absorption spectra of phosphorus and nitrogen. The experimental conditions of the samplecolor determination are determined through orthogonal experiment for four factors andthree levels. TP: suction time of flow path is370s, speed of pump is16×8, collecting timeis after standing900s and points of acquisition are100. TN: suction time of flow path is370s, speed of pump is16×8, collecting time is after250s and points of acquisition are500.The device performance is tested using Qingdao seawater samples and Chinese seriesstandard seawater. The detection limit of total phosphorus is0.00192μg·mL^-1and thedetection limit of nitrogen is0.0307μg·mL^-1. In the precision experiments of laboratoryreagents, the relative standard deviation of phosphorus is7.06%and the relative standarddeviation of nitrogen is2.17%. In the precision experiments of actual seawater, therelative standard deviation of phosphorus is2.43%and the relative standard deviation ofnitrogen is2.23%. The average recovery of TP is91.58%and the average recovery of TNis94.25%.The device is integrated into the ship named “Xiang Yang Hong08” belonging toQingdao Sea Marine Engineering Investigation Institute. The system runs in Bohai Seaand the comparison test and inspection of the online automatic monitoring device for TPand TN in seawater are done. The systems of data processing and transmission are tested.The results show that the detector is relatively stable and accurate. The detector will beimproved and perfected and it will be more adapted to the marine monitoring.