| PAHs and its derivitives is a sort of important organic pollutants which are persistent.For their carcinogenicity, teratogenicity and mutagenicity they have been put on the priority list to be detected by Environmental Protection Agency (EPA). Their carcinogenicity increase as the number of benzene ring increase (So far, there have been more than 400 kinds of PAHs and its derivitives found). The study on PAHs and it derivitives has become a hotspot issue. Domestic sewage and industrial waste water are a major source of the PAHs. So the municipal sewage treatment plants play a very important role in keeping down and blocking PAHs into natural waters. In recent years many developed countries and regions have already started doing research on PAHs in municipal treatment plants. However, the similar research has rarely being reported sofar.This research selected EPA PAHs 16 as the objects, and established the method of Solid Phase Extraction-Gas Chromatography (SPE-GC) which is suitable for concentration and analysis of PAHs in waste waters. The research did a long-term measuring to the categories and contents of PAHs in waters of different phases in the Xi'an Third Municipal sewage treatment plant, and preliminarily determined the distribution of PAHs in waters of different phases and their rules of transformation. This research also investigated the effectiveness of PAHs removal by traditional methods. The research intended to provide a foundation for keeping down POPs and PAHs in the future. The research concluded as follows:(1) In order to improve the coefficient recovery of PAHs, a series of condition-optimized experiments were conducted to determine the best condition of solid phase extraction:C18 as the absorbent of solid phase,6.42 PH value of water samples, adding about 10% of organic improver (methanol) in terms of volume into waters samples. And the experiment should be conducted with a volume of water sample 500ml, the speed of water sample flow 5mL/min, eluent of methylene dichloride with a volume of 8ml.(2) The research determined the best gas chromatography condition of PAHs, and separated the 16 PAHs efficiently in about 30 minutes. The results showed that the calibration plots of 16 substances are well correlated with the correlation coefficient about 0.99.(3) The established SPE-GC method in this research has better precision and accuracy. For the poor thermal stability only naphthaline has the recovery coefficient of 56.67% and the relative standard deviation (RSD) of 23.42%. The other 15 PAHs have better precision and accuracy with the recovery coefficient in the range of 72.67%-105.58%, and RSD in the range of 2.94%-14.34%. The method detection limit can meet the detection requirement with a range of 2.9-84.6ng·L-1.(4) The research which detected PAHs in Xi'an Third Municipal sewage treatment in 8 months showed that concentrations of PAHs in raw water are very high in November, December and January. And from March to June concentrations are a bit low. According to the number of their cyclics, the concentrations of PAHs appeared different in different seasons. The 13 different kinds of PAHs detected in raw water can be listed in terms of concentrations from high to low as follows:naphthalene, phenanthrene, Fluorene, Pyrene, Chrysene, acenaphthylene, acenaphthene, anthracene, Benzo(a) anthracene, flua, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene; The total quantity of PAHs in raw water is between 477.1-3067.7ng·L-1 with an average value of 1883.1ng·L-1, which is at the middle level compared with the results reported abroad; The secondary treatment can remove PAHs efficiently, with a removal rate of 79%. And the biologic unit contributes most with a removal rate of 68%. The PAHs removal rate in oxidation ditch does not have clear relativity with the removal of total organic carbon, ammonian, total phosphorus, infilterable residua, filterable residua and turbidness.
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