Environmental Behavior and Photodegradation of Organic Pollutants in the Supergene Environment of Huaihe River

淮河流域表生環境中有機汙染物的環境行為及其光催化降解研究

Student thesis: Doctoral Thesis

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Author(s)

  • Jiamei ZHANG

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date18 Jun 2014

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants (POPs), possessing strong carcinogenicity, mutagenicity, and toxicity. PAHs are emitted mainly by the incomplete com bustion or pyrolysis of organic-rich materials, such as fossil fuels and wood. The U.S. Environmental Protection Agency (US-EPA) has defined sixteen PAHs as priority pollutants. PAHs from natural and anthropogenic sources can be released to the soils, sediments, groundwater, surface water and biodiversity in particulate and gaseous forms.

Bank surface soil samples from the middle reaches of the Huaihe River were analyzed by GC-MS for PAHs in 2013. The total PAHs concentrations ranged from 104 to 947 ng/g in bank soils. The PAHs levels of studied samples are relatively higher compared with those from other regions of the world, which suggests an enhanced deposition of atmospheric PAHs derived from the emissions of fossil fuel combustion in this area. The possible sources of PAHs in soils were diagnosed by the paired PAHs isomer ratios and principal components analysis (PCA), and the results indicate that the PAHs in soils mainly came from coal combustion (74%) followed by combustion of refined petroleum products (26%). However, the calculated total toxic BaP equivalent of PAHs in soil indicates that BaP is the most potentially carcinogenic individual PAH.

343 water samples from 104 sampling sites in 2009, 2011 and 2013 were collected from eleven locations on the middle reaches of the Huaihe River to evaluate the environmental effect of local urban and industrial activities. The total concentrations of PAHs in the studied water samples ranged from 1.2-5.1 μg/L in 2009, 0.86-408 ng/L in 2011, and 47.9-114.8 ng/L in 2013. The PAHs concentrations in studied water samples in 2013 are significant lower than those from 2009 and 2011. The highly heterogeneous distribution of PAHs in either the spatial or vertical water column relates to local contamination sources and PAHs migration among the atmosphere, water and sediment. The PAHs sources in the middle reaches of Huaihe River in 2009 are mainly coal combustion (34%), oil spills (49%) and vehicular emissions (17%). On the other hand, PAHs in 2011 are mainly from pyrolytic sources such as the combustion of coal and coke, with the addition of a mixture of emissions from the steel industry and gasoline. In addition, the responsible PAHs loading in the middle reaches of Huaihe River in 2013 are mainly from the mixture of pytrogenic and petrogenic types. Risk assessment of PAHs during the four years indicates that the studied water column poses limited PAHs toxicity to the environment.

106 sediment samples from 106 sampling sites were collected from the middle reaches of the Huaihe River in 2009, 2011 and 2013. The PAHs concentrations in sediments in 2009 ranged from 72 to 139 ng/g, while from 83 to 2599 ng/g in 2011 and from 46 to 332 ng/g in 2013. The total concentrations of PAHs at 2013 (68 ng/g) are lower than those in 2009 (91 ng/g) and 2011 (525 ng/g). This is probably because that the government paid attention to pollution control, and the complex aquatic environment. The calculations of Ph/An and Fl/Py in sediments in 2009, 2011 and 2013 showed a “mixed” contamination pattern. The PCA results clearly showed that the sources of sediment PAHs in 2009 were the emissions of coal combustion, while the mixed coal and refined petroleum products combustion and oil spill emissions were the main PAHs sources in sediments in 2011 and 2013. Assessment of ecological risks indicated that the toxicity of PAHs in 2009, 2011 and 2013 were not significant in sediments.

Photocatalysis with photocatalytic water splitting under visible light irradiation is a green technology for solving the new energy and environmental problems. Therefore, the nanomaterials of urea-C3N4 (UCN) and melamine-C3N4 (MCN) were successfully synthesized. The organic pollutant employed during the photocatalysis was RhB. Based on the large surface area of UCN, the photocatalytic activity of UCN is higher than those of MCN and TiO2. In addition, to improve the activity photocatalysts, In2S3-doped UCN was synthesized with different weight percentages. The photocatalytic activity of 8:2 In2S3/UCN is significantly higher that of other weight percentages of In2S3/UCN and TiO2 under visible light irradiation. In order to produce hydrogen generation, different weight percentages of NiS/C3N4 were prepared. During hydrogen evolution, 7% NiS/C3N4 has a higher photocatalytic activity than those of other weight percentages of NiS/C3N4. In addition, the different reaction conditions of NiS had a strong influence on the photocatalytic activities.

    Research areas

  • PAHs, soil, water, sediment, Huaihe River, Semiconductor, Photodegradation