| Seawater Chemical Oxygen Demand (COD) indicates the contents of organicpollutants in seawater, thus is one of the most important items of routine monitoring.Seawater COD supplies the basis of marine pollution assessment and disasterforecasting. Studying the control factors and monitoring technologies can help fullyunderstand the environment quality and its variation of the multi-media integratedmarine, in order to decrease the contradiction between marine economy developmentand environment pollution.In the current COD measurement rely on the laboratory technologies, in whichalkaline potassium permanganate method is the national standard COD measurementof seawater. The standard method has a series of complex procedures and consumes along time. However, the organic pollutants in our marine is largely complex for theseries of physical, chemical and biological processes and the influence factors such asthe quality and concentration of organic pollutants, the coastal topography, thehydrological conditions, the microorganisms in water, water temperature and oxygenconditions etc. That is, the type and concentration of organic pollutants vary in thespace and time scales; therefore, the current COD measurement can not meet thein-situ studies at both the small and large scales. In addition, disaster forecasting is theaim of marine environmental monitoring and protection, which rely on the accuratein-situ technologies. Therefore, it is critical to study the in-situ equipment of CODmeasurement.The instrument of in-situ COD measurement can help the marine scientists tounderstand the COD variation and its control factors, which supply the data forevaluation of the marine environmental pollution and study of the marine ecology. On the other hand, the equipment can effectively reduce the labor intensity in marinesurvey and monitoring and improve the response capabilities on the marine pollutionemergency.We developed an in-situ measuring instrument of seawater COD based on therecent development on the COD measurement in seawater and apply it in two marinesurveys. The main conclusions are as follows:(1) the instrument based on the ozonation chemiluminescence theory has nosecondary pollution, analysis rapidly, work in ship, marine stations, offshore oilplatforms for a long-term. The instrument avoids the complex procedures in thesampling, stock, transportation, and laboratory analysis, also realize the in-situmonitoring of COD, enhancing the capabilities of marine environment monitoring.(2) The PC software is written by VC++, including a variety of processes, suchas signal acquisition and optimization processing, operations of analysis andmeasurement, real-time display of monitoring curves, man-machine dialogue, etc.With the software, the instrument can achieve a set of functions, such as automaticcontrol, real-time analysis and calculation, real-time display of monitoring curve, datastorage and playback, etc. With the software, a variety of measurement modes can beset according to the actual requirements. The testing in the laboratory and fieldshowed that the software is stable and its function performs well.(3) A working curve (y=0.033x+0.0503, R~2=0.9955) was first developedbased on the system testing and laboratory analysis by the instruments. Resultsshowed that the working curve meet the measurement requirements. Then theinstrument was tested its measurement accuracy, precision, and detection limit.Results showed that the instrument accuracy is±0.1mg/L when the COD in thesample is less than1.0mg/L, and the accuracy is±10%when the COD is greater than1.0mg/L; the precision is10%and the detection limit is0.08mg/L, lower than thedetection limit (0.15mg/L) of the alkaline potassium permanganate method(GB17378.4) the detection limit. COD is a water condition parameters, while theinstrument used in principle with the GB method is different, thus anotherexperiments were used to test the recovery rate and linear relationship between the instrument and the standard method. The recovery rate is in the range of90-120and a high linear relationship was in the instrument. Therefore, the instrument fullymeet the in situ monitoring in that the data measured by the instrument has a highlinear relationship with the national standard method.(4) The instrument works well during two sea trials in the Jiaozhou Bay. The datadifference between the instrument measurement and the national standard method isin the normal error range. Therefore, the instrument can meet the in-situ survey formarine water quality, marine environment research, marine pollution warning,assessment and forecasting of marine pollution. |
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