| In order to fully understand the occurrence of mercury in dewatering sludge of municipal sewage treatment plant in China,315 samples of sludge were collected from40 municipal sewage treatment plants nationwide,the mercury content in municipal sludge samples was determined by DMA-80 Direct Mercury Analyzer,and the toxicity leaching experiment of sludge samples was carried out according to Toxicity characteristic leaching procedure?TCLP?.The single factor index method and the cumulative index method were used to evaluate the pollution.The results show that:?1?The mercury content in municipal sludge samples in China accords with logarithmic normal distribution,the content range is between 0.45-15.42 mg kg-1,and the geometric mean is 2.19±3.16 mg kg-1.The mercury content of the municipal sludge in different areas is quite difference,the coefficient of variation is 105%,the mercury content of sludge in the same sewage treatment plant is also unstable,the seven-day variation coefficient is between 0.6%-53.56%.The content range of effective Hg in sludge was measured by TCLP method between 1.75-7.26?g kg-1 and the geometric mean was3.58±0.24?g kg-1.?2?It can be seen from the spatial distribution of mercury content in municipal sludge in China,the mercury content in the sludge is gradually decreasing from north to south,according to the 7 regions of China,the median value of Hg in the sludge obeys North China and northeast China,northwest area and east China The spatial distribution trend in South China.?3?Comparing and analyzing the historical data of the literature report,we found that the arithmetic mean value of Hg in the sludge in different time periods was:1.45±1.82 mg kg-1?1982-1999?,4.97±4.71 mg kg-1?2000-2009?,2.62±2.91 mg kg-1?2010-2015?,of which the mercury content in the national sludge peaked in 2000-2009,and with the development of China's PVC industry and the trend of mercury consumption is basically consistent.?4?The evaluation result of single factor index method shows that the pollution index of Hg in the sludge was not more than 1,which indicated that all the mercury content of the samples was in compliance with the standard of sludge landfill stipulated in the sludge disposal of municipal sewage treatment Plant?GB/T 23485-2009?.97.8%of urban sludge mercury content meets the Municipal sewage Treatment Plant sludge disposal land improvement with mud?GB/T 24600-2009?,the standard of alkaline soil control,only some samples of hohhot slightly exceeding the standard;86.7%of the City sludge Mercury content to meet the GB/T 24600-2009 of the acid soil control standards,only Hohhot,Lhasa,Ordos,Shihezi,Changchun City,Beijing 2 do not meet the standard,the sludge used for land improvement should pay attention to distinguish the nature of the soil.?5?According to the Soil National standard?GB/T 15618-1995?,the natural background value of mercury in primary standard and the soil background value of each capital city are referenced,using the cumulative index to evaluate the content of mercury in the sludge,it was found that the proportion of pollution was more than 60%,It shows that the risk of mercury pollution is still serious.The effective mercury content in municipal sludge was measured by TCLP method below international standard limit,which indicated that mercury in sludge would not cause pollution in the short term. |
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