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Study on Online Determination Technique of Nitrate Nitrogen and Orthophosphate Phosphorusin the Digested Seawater

Author: FuXiaoWen
Tutor: WeiFuXiang
School: Hebei University of Science and Technology
Course: Environmental Engineering
Keywords: sea water determination nitrate nitrogen orthophosphate phosphorus online automatic monitoring device spectrophotometry
CLC: X832
Type: Master's thesis
Year: 2009
Downloads: 24
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Abstract

With the development of the people’s quality of life and the level of industry, the quality of the marine environment is subjecting to an unprecedented pressure. Eutrophication in seawater has become a major cause of pollution affecting the marine environmental quality. The toxic red tide, as a result of eutrophication, makes human health and economic development come to serious harm. High concentration of nitrogen and phosphorus nutrients is the main factor leading to eutrophication of marine water. Total nitrogen and total phosphorus has become an important indicator to monitor marine water quality. But the traditional monitoring methods based on manual sampling and laboratory analysis has relatively long measurement cycle, complicated procedure and cannot achieve real-time monitoring of the target. They can no longer meet the current needs of the marine environmental quality monitoring. Automation, intelligent and networked monitoring method for monitoring the marine environment will become the development direction of marine environmental science. Therefore, developing a set of online automatic devices to monitor total nitrogen and total phosphorus in seawater, and achieving continuous, online and fast deter mination of marine water quality have great significance to improve the monitoring level of China’s marine water quality.This paper selected visible spectrophotometric as the online automatic deter mination method of total nitrogen in seawater. And the method is optimized to make it suitable to seawater. The chromogenic conditions are: adding sulfanilic acid solution(4 g·L^-1) 1.0 mL, reacting for 1 min, adding hydrochloric acid naphthyl ethylenedia mine(2 g·L^-1) 0.75 mL, the chromogenic time is 5 min, and measuring the absorbance values at a wavelength of 519 nm with the non-ammonia water as the reference. The conditions for deter mination are: the diameter of cadmium particles is 2⁵ mm, the length of the cadmium column id 10 cm, the residence time is 480 s, pump speed = 2 r·min^-1, the reduction temperature is 20℃³5℃, pH is 2.5 to 4.0. And, the reduction efficiency can be stabilized at more than 95%. Under these conditions, the deter mination of total nitrogen concentration in seawater has low detection limit, good precision, and the specification curves of sodium nitrite and reduced potassium nitrate both have good linear relationship.The method of visible spectrophotometric deter mination of orthophosphate phosphorus is improved to make it suitable to the needs for designing the on-line automatic monitoring device. The conditions for deter mination are: adding A reagent (0.3 g·L^-1 ammonium molybdate sulfuric acid solution) 2.0 mL, shake, preparation for 30 s, adding B reagent（compound of antimony tartrate potassium, anhydrous sodium sulfate and ascorbic acid solution） 5.0 mL, the chromogenic time is 15 min placed, and measuring the absorbance values at a wavelength of 710 nm with the pure water as the reference. Under these conditions, the deter mination of total phosphate concentration in seawater has low detection limit, good precision, and the specification curve of potassium dihydrogen phosphate has good linear relationship.This paper selects the water in the lake of Chang’an Park in Shijiazhuang, seawater of Gold Coast in Qinhuangdao and seawater near Zhanqiao Pier of Qingdao as the representative water samples. The contents of total nitrogen and total phosphorus are determined. The results are satisfactory.The online and automatic monitoring device of total nitrogen and total phosphorus in seawater is preli minarily designed. And it is enable to meet the requirement of the online deter mination of total nitrogen and total phosphorus in seawater. The function of main hardware devices is introduced and the drawing of the flow path design of the device is drawed. The way to achieve simultaneous digestion of total nitrogen and total phosphorus and separate deter mination of the flow path are described.

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CLC: > Environmental science, safety science > Environmental Quality Assessment and Environmental Monitoring > Environmental monitoring > Water quality monitoring
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