| The characteristics, biological leaching of heavy metals, and safely agricultural application of some municipal sludges in Shanxi Province on calcareous soils were studied with indoor experiment and pot experiment. The conclusion was as follows:(1) The results of municipal sludge analysis showed that the pH values of the 13 municipal sludge samples collected from different sewage treatment plants in Shanxi Province was in the range of 6.76-7.78, the organic matter contents were in the range of 18.5-68.8%, the content of N+P2O5+K2O were in the range of 3.03-21.39%, the heavy metal contents of Cu, Zn, As, Hg, Pb, Cd, and Cr were in the ranges of 61.1-225.4,76.2-1557.1,11.5-29.1,0.2-1.7,13.5-89,0.5-8.6, and 108.9-328.1 mg/kg respectively. The contents of Zn and Cd in the sludge from Changzhi sewage treatment plant exceeded the imiting values of class A sludge and the content of Cd in the sludge from Taigu sewage treatment plant exceeded the imiting value of class B sludge in the agricultural using sludge quality standard (CJ/T309-2009), the contents of heavy metals in sludges from the other sewage treatment plants all met the limiting values of class A sludge in the agricultural using sludge quality standard (CJ/T309-2009). According to the heavy metal contents of farmland soil in the different areas of Shanxi Province and the secondary standard of soil environmental quality, the environment capacities of soils to heavy metals in the different areas of Shanxi Province were Pb> Zn> Cr> Cu> As> Hg> Cd. Based on the annual sludge application quantity of 7500 kg/hm2, the continuous sludge application time was 106 and 131 years in Datong city,160 and 248 years in Shuozhou city, and 88 and 187 years in Xinzhou city in the areas of northern Shanxi Province. The continuous sludge application time was about 6 years in Taigu County of Jinzhong areas and about 105 and 282 years in Jincheng city and 17 and 100 years in Changzhi city in the southeast Shanxi Province.(2) A pot experiment was conducted with 8 sludges selected from the 13 municipal sludges based on organic matter content (less than 40%,40-60%, more than 40%) and 4 application levels (0,6,12, and 18 g/kg soil) to study the effects of different sludges and application doses on soil fertility and crop growth. The results showed that the plant height, root length, and dry weights of up-ground and underground parts of first crop maize in seedling stage all firstly increased and then decreased as the application doses of the 8 sludges increased and the most of the above indicators were the highest as the application doses of the 8 sludges was 12 g/kg soil. But the plant height, root length, and dry weights of up-ground and underground parts of second crop rope in seedling stage most increased as the application doses of the 8 sludges increased.The soil organic matter, nitrogen, phosphorus, and potassium contents all increased as the sludge application dose increased at the seedling stage of the two crops and the effects of sludge with higher organic matter and nutrients were bigger on soil organic matter and nutrients. Application of sludge increased the contents of N, P, and K in plants of the two crops at seedling stage and their contents in plant of first crop maize were lower than that in the plant of second crop rape.The contents of total Cu, Zn, Pb, Cd, Cr, and As of soil were all increased as the application dose of sludge increased and their contents at second crop rape were lower than that at first crop maize. The heavy metal contents of soil treated with sludge were all not more than the limiting values of agricultural land secondary standard in "soil environmental quality standards" (GB15618-1995). The major form of Cu, Zn, Pb, Cd, and Cr were residual state in the soil applied with sludge.The influences of application sludge on the total Cu, Zn, Pb, Cd, Cr, and As contents in plant of the first crop maize and second crop rape were that the contents of heavy metals in underground part of maize at seedling stage were higher than that in up-ground part of maize and the contents of heavy metals in up-ground part of rape at seedling stage were higher than that in underground part of rape.. Comparing with limited national hygiene standards in the food, the contents of heavy metals in the plants not exceeded the maximum limiting values of the standards at the application sludge dose of 12 g/kg soil, but the contents of Cu and Zn in the plants both exceeded the limiting values of the standards at the application sludge dose of 18 g/kg soil.(3) The results of biological leaching experiment of sludge heavy metals showed that the removal rates of Cu, Zn, As, Cd, and Cr from natural dried sludge samples reached 23.69%to 77.62%,89.67%to 97.80%, 77.62% to 89.67%,18.18% to 97.05%, and 28.55% to 97.05% respectively and the loss rates of organic matter, total nitrogen, total phosphorus, and total potassium from sludge were 3%,1%,44%, and 3% respectively. |
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