| Nowadays people have high standards for drinking water. The odor problem of water has also been widespread concern. As the research object, an eutrophic reservoirs-Zhoucun Reservoir was investigated to find out one of the main reasons of water odor-the release of volatile organic sulfur compounds(VOSC). According to establishing an accurate method of detecting VOSC and a situ monitoring to VOSC in Zhoucun Reservoir, the research has explored the spatiotemporal variation of VOSC in water. In addition, simulated release of VOSC in the lab, under different levels of dissolved oxygen, to find out the release regularity and varied characteristics of related substance involved in release processes. The main results are as follows:(1) A method for detecting VOSC in reservoir water sample was developed and optimized using purge and trap(P&T) coupled with gas chromatography(GC)-mass spectrometry(MS). It had optimized the shape and area of substance peaks and shortened the detection time. Also it could accurately and efficiently detect the test substance from the water sample which has a complex composition. The linear correlation coefficients of the method were between 0.9951 and 0.9994. The average rates of recovery were between 97.5% and 98.0% and the relative standard deviation was less than 3%(n=7). The limits of detection(3S/N) were between 7.9ng/L ~23.7ng/L. The method established in the study is accurate, sensitivity and repeatable.(2) The results indicated that the main VOSC were ethyl mercaptan and dimethyl trisulfide during monitoring Zhoucun Reservoir. These substances were mainly produced by degrading organic sulfur compounds and reducing sulfate. They were typically strong malodorous compounds in water. The content of them changes mainly affected by temperature and dissolved oxygen. The odor problem in water reservoir broke out seasonally and the most serious period was summer. The concentration of ethyl mercaptan and dimethyl trisulfide respectively reached range of 18.59μg/L~44.37μg/L and 0.17μg/L~0.39μg/L. Reservoir thermal stratification and intensified material exchange between sediment and overlying water, which was the main reason on seasonal odor problem. The content of VOSC increased with water depth, which related to the anaerobic environment formed in the bottom of the reservoir. In situ aeration experiment proved that,when aeration volume was 15L/h, water-lifting aerator could enhance the content of dissolved oxygen efficiently, mix water thoroughly, reduce the content of VOSC obviously, and improve the water odor problem. The removal rates of ethyl mercaptan and dimethyl trisulfide were respectively more than 90% and 80%.(3) Controlling the content of dissolved oxygen, the experiment simulated the release process of VOSC in water. The result showed that VOSC released massively only in anaerobic environments and the release happened abruptly. Different substances broke out at different times. In the anaerobic environment, the variation of sulfide content in water had an opposite tendency with sulfate. During this process, the content of sulfide was increasing while sulfate were reducing. The reason is that sulfate-reducing bacteria in the sediment had high activity when environment is anaerobic and reduced sulfate to sulfide. After reached a certain content, sulfide would transform to hydrogen sulfide and escape from the water. At the same time, a large number of VOSC were released, make the water malodorous. Since sulfate-reducing bacteria and methanogenic bacteria inhibited with each other, the rate of production of hydrogen sulfide and methane were in contrast. In the late sulfate-reducing bacteria became dominant bacteria. The contents of hydrogen sulfide and methane escaped from water increased simultaneously. Strong reduced state caused by anaerobic environment increased ferrous ion content and ferrous sulfide precipitate was generated by reaction between ferrous ion and sulfur, so that more sulfate transformed to sulfur ions and VOSC released on a large scale. |
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