| Dissolved organic carbon (DOC) is an indicator of total amount of organic matters in aquatic system. It can not only reflect the extent of pollution by organic matters but also the status of aquatic living as a kind of biogenic elements. DOC also plays an important role in research of total carbon cycling. DOC has become regular required parameters in water quality monitoring, measurement of which has involved in river, lake, ocean, and so on. DOC measurement has become a main method for water treatment and quality control in many countries, and is also one of water pollution indicator in China. There are more or less flaws existed in DOC analyzer at present, for example, low sensitivity and not suitable for DOC analyzing of seawater for homemade analyzer; high price and high cost, which hinder the daily uses for some institutions, for imported analyzer. Therefore the situation now doesn't meet the requirement of marine chemistry development, and new DOC analyzer of low cost and high sensitivity is needed. In order to resolve this problem, author of this thesis manufactured a high sensitivity and low cost DOC analyzer, which could be used on board for on-site rapid analyzing.This analyzer was based on ultraviolet-potassium persulphate oxidation method, and DOC concentration calculated by standard curve method with CO2 produced by non-dispersive infrared detector. Six-way valve and bubbling after acidizing were used in sampling and drive-off inorganic carbon, respectively. Air and high-purity water were used to separate samples. The oxidant was a mixture of 35 g/L potassium persulphate and 70 g/L sodium borate. The results show that the oxidant can acquire about 100% oxidation efficiency.The software programs such as communication, calculation, print, man-machine dialog, and so on for analyzer were processed by visual basic advanced language. The functions, for example, automotive control, analyzing, monitoring and alert, parameters setting, graph display, man-machine conversation, data save and export, and so on could be well realized. The setting of parameters, control of temperature in oxidation chamber, calculating by signal peak, processing data automotive, and man-machine dialog with touch screen could all be realized. All the functions worked well according to the result of on-site test.The detection limit of this analyzer was 0.038 mg/L. The accuracy were 7.14%, 3.14%, and 4.08% when concentration of DOC samples were 1.00 mg/L,1.50 mg/L, and 2.00 mg/L. The standard deviation of 10-day continuous analyzing of 1.0 mg/L, 1.5 mg/L and 2.0 mg/L DOC samples were 3.4%,4.4% and 3.3%, which meet the requirement of machine's stable state.Compared some data obtained from two apparatuses, which are the home-made analyzer and the Shimadzu analyzer for the type of TOC-VCPH, and the samples were gathered from Changjiang River and Qingdao coast. The results show that the relative errors vary from 5.6%(seawater) to 5.9%(river water), and the errors are in the normal scope. Within the degree of confidence of 90%, there was no significant difference from two analyzers by the method of F-test.According to the results of DOC investigation to offshore water in Qingdao, the effect of biogenic elements in the growth and disappearance of Enteromorpha prolifera was investigated. It was shown that the concentration of dissolved organic carbon (DOC) increased and then decreased in that period. The similar trend was found in chlorophyll-a and COD (Chemical Oxygen Demand) but not in nutrients. The variety rule of nutrient shows the double effects of marine organism and land drainage. Among the nutrients, the concentration of phosphate is much lower, and proved to be the confinement factor for the growth of phytoplankton in the researched sea area. The dissolved inorganic nitrogen and active silicate were affected little by Enteromorpha prolifera.
|
PDF Full Text Request