| As it is known to all, sludge composting is an effective way of sludge recycling. On one hand, the application of composting product to the extensive desert land could solve the problem of sewage sludge disposal. On the other hand, it would be a positive factor to the soil structure of the desert land, improving the surrounding environment of the desert land. However, there are many problems that we should really care about. Whether or not the composted municipal sludge could improve the physicochemical properties of the desert land soil and the growth of plants. Would it bring some potential threats to ecological ambient medium? In order to answer the questions above, taking composted municipal sludge from Panggezhuang Sludge Composting Plant for research object, this article investigated the effects of applying composted municipal sludge on the physicochemical properties of desert land soil and the growth of plants with a combination of the variation of heavy metals and PAHs in ambient media in Yongdinghe area, providing a theoretical reference and practical support for the usage of composted municipal sludge in desert land.A pot-scale test was carried out to investigate the effects of applying composted municipal sludge on the physicochemical properties of desert land soil and the growth of tall fescue and ryegrass. The results showed that after the application of composted municipal sludge, pH of the soil was more suitable (6.0-7.0) for the growth of tall fescue and ryegrass. At the dosages of 10%,25% and 50%, electrical conductivity (EC) of the soil was 11.93,12.66 and 19.81 times that of the soil without composted municipal sludge adding, indicating that the application of composted municipal sludge can significantly increase the electric conductivity (EC) value of it. Besides, the contents of TN, TP, TK and the soil organic matter (SOM) increased with the application rates correspondingly. For example, at the dosages of 10%, 25% and 50%, the content of SOM was 3.69,4.22 and 5.65 times that of the soil with no composted municipal sludge adding. Futhermore, applying composted municipal sludge could accelerate the nutrients absorption of the plants and it would be an important promoter to the growth of it to some degree. Nevertheless, such slow promotion did not reveal in the earlier studies until the later stage.In addition, the field test that covered two parts was put into effect on the riverbed of Yongding River in Daxing District, combining with the ten-thousand-mu-afforestation-project in Beijing. Through the continuous monitoring and analysis of the variation of heavy metals and Polycyclic Aromatic Hydrocarbons (PAHs) in different environmental samples (soil, surface water, undergroundwater, the branches and leaves of plants) from different sites, we can come to the conclusions as follows:no matter which fertilization way we used (hole applying or mixed plowing), both of the contents of heavy metals and PAHs accumulated with time to a certain extent, comparing to the soil background. Moreover, the soil quality would not return to the original level in a short time. Contents of heavy metals in surface runoff were closely related to the relevant contents in the rain. There was no migration of heavy metals to the underground water in the short term. However, for the lag of heavy metal pollution, we still could not rule out the threat of heavy metals to the underground water from the short-term monitoring results. Only six 2-3 ring PAHs with low molecular mass and high water solubility were detected in the surface runoff and underground water, and the contents of PAHs in runoff increased by the application ratio of composted municipal sludge. In addition, in terms of two fertilization ways (hole applying and mixed plowing), the content of PAHs in runoff of mixed plowing site were a little higher and it might play an invisible role in the PAHs migration from soil to runoff. So far, we have not found a clear regularity of the variation of heavy metals and PAHs in the branches and leaves of plants through such a short-term experiment. |
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