| Recent years, disposals of sludge producted by the process of Municipal Wastewater Treatment and the environmental influence have received more and more attentions. Heavy metals in sludge were main obstacles to the diaposal of land use, thus we began this research with expectation of providing scientific reference and resource utilization. This study analysed characteristics of Huainan municipal sludge using field investigation, the mainly studies as following: understanding the basic physical and chemical properties of municipal sludge; evaluating on farm safety using over standard individual evaluation indexes and Nemorow comprehensive evaluation index of Huainan municipal sludge;monitoring and analysing treatments of different municipal sewage sectiones and heavy metal contents in sewage continuously, seeking laws of the heavy metals transport and transformation; laws of pH on heavy metals migration and bioavailability in sludge;the relationship between extractability and bioavailability,and so on.This paper studied on Huainan sludge from the First Municipal Wastewater Treatment Plant, the mainly study results as following: (1) Compared with soil, the municipal sludge generaliy showed high organic,high nitrogen and phosphorus,low potassium,high nutrition,having good agricultural value, Zn and Cu were the main heavy metal pollutants. (2) Evaluating on farm safety using over standard individual evaluation indexes and Nemorow comprehensive evaluation index, single index of all heavy metals didn't exceed for this Wastewater Treatment Plant,comprehensive pollution index didn't exceed 1.Those showed that the Huainan municipal sludge were up to the standards of agricultural municipal sludge in China.(3) All five heavy metal contents were different for different sewage treatment sections, that had relationship with heavy metals removal efficiency in each section. The removal efficiency of Cu in the grit chamber and oxidation ditch were similar; Zn, Pb, Ni were removed in the grit chamber mostly, while Cd mainly in the oxidation ditch. Compareed with heavy metal contents distribution in sludge samples of different section, sediment heavy metals in the sludge were not remarkable different. Cu was mainly distributed in oxidizable state, Zn and Ni were mainly distributed in the exchangeable state and the reduced state, Pb major distributed in the residue state and the exchangeable state, Cd were mainly distributed in the oxidizable state. In addition, the percentage of exchangeable state Zn and Ni were more than 40%, potential migration and phytotoxicity deserved the most attention. (4) pH affected forms distribution of heavy metals in sludge obviously, the percentages of exchangeable state heavy metals in the acid sludge were significantly higher than other sludge. Low pH could decreased the adsorption rates of samples to heavy metals and promote released heavy metals. On the contrary, high pH could inhibit the release of heavy metals and promote the sediment heavy metals. (5) Enrichment ability of different organizations of wheat seedlings to the same heavy metal were different, the contents enriched in roots were higher than those of stems and leaves. In the five extractants of this study, there was a good correlation between heavy metal contents extracted from EDTA and heavy metal contents enriched in the wheat seedling roots,that showed EDTA could be the most excellent chemical extractants as evaluating potential bioavailability of heavy metals.
|
PDF Full Text Request