| Beijing is located in the northwest of north China plain and characterized by temperate semi-arid-humid monsoon climate. The lack of nature resource and the scale of urban development lead to the situation that sewage irrigation has been an important measure to solve the problem of agriculture water shortage in Beijing. Liangshui River is the second drainage river of Beijing, and it is also the main sewage-irrigated canal in Tongzhou area. The discharge of industrial wastewater and domestic sewage deteriorate the water environment, and organic pollutants can transfer into soil through sewage irrigation, to plant and/or animals subsequently, ultimately hazard human health.Samples were taken separately along the Liangshui River of Tongzhou area (Beijing) to investigate the water quality and study the transport, distribution and characteristics of organic contaminants in water, suspended solids and sediments, analyse the effects of invisible pollution on water environment and ecosystem, and estimate the security of using sewage for irrigation. At the same time, blank electrolyte was replaced with sediment extract to guarantee the aqueous chemical consistency. Batch equilibrium experiments were carried out to investigate the sorption and desorption behavior of naphthalene on and from two representative sediments (denoted as L and D, respectively), found out the significance of aqueous chemistry consistency on sorption and desorption process.The results indicated that the average concentration of COD exceeded the values stipulated for water of Class V in all sections, while the phenols concentrations in water were below Class V , both of them met Standards for irrigation water quality. The NH3-N, TN, TP concentrations exceeded the values stipulated for water of Class V too, trophic state index showed that the Liangshui River in Tongzhou area was in serious eutrophication condition; There were 7 kinds of organic compounds detected in Liangshui River, including PAHs, benzene series, esters, phenols, alkanes,nitrogenous heterocyclic and oxygen heterocyclic. Choose PAHs, phenols, phthalic acid esters, benzene series as target pollutants to conduct quatitative analysis. It is found that phenols and benzene series were the dominant pollutants in water, but the suspend solids and sediments contained more PAHs and benzene series. The average concentration of these pollutants in suspended solids were 72.70,3.94,12.45 and 3.00 mg·kg-1, more than that in the water and sediments; Sorption and desorption of naphthalene from sediments exhibit obvious hysteresis as described by the hysteresis index (HI). Traditional desorption method decreased the TOC by 74.68%-85.01% as compared with extracts. Greater hysteresis exists in blank electrolyte than that in the sediment extracts, as indicated by the larger HI values of 0.04 and 0.135 in blank electrolyte than those of 0.012 and 0.072 in the sediment extracts for the sediment L and D respectively. Meanwhile, the average concentration of TOC in the extracts increases 3.14 and 2.40 mg·kg-1 more than in blank electrolyte. This research demonstrates that the average desorption of naphthalene increased significantly in sediment extract, and the results would be more accordant with the condition of nature water.
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