Contents and distribution of mineral elements in urban and industrial sludges in Nanjing

This paper aims to introduce the authors' investigation on the contents and distribution of mineral elements in the urban and industrial sludge in Nanjing City. The sample sewage sludges tested in this paper were collected from Suojincun sewage treatment plant, Jinlin Petrifaction Co. Ltd. wastewater treatment plants, Jianglin Beer Industry wastewater treatment plants and Jinyinxin Paper Industry wastewater treatment plants in Nanjing. As we know, mineral elements are necessary for the plant growth and development. The content of mineral elements in sludge can help to provide information on their bioavailability than their total contents. The physicochemical properties of the sludge and the total contents of the mineral elements and their fractions by BCR sequential extraction were investigated. As a result, it was found that the sludge contains organic matters, such as TN, TP to a high degree but K to a low degree. Their CEC and pH varied greatly. The difference of the mineral contents in the sludge samples collected was significant. So were the difference in the kinds of the mineral elements in the different sludge samples. Generally speaking, Fe was the highest, and followed by Mg, Zn. The fractions obtained by the sequential extraction procedure indicate that Zn fractions were affected by the source of the sludge samples, and their percentage were all above 10%; Cu was principally distributed in the oxidizable fraction; Mg and Mn were principally distributed in the acid soluble/exchangeable fraction and Fe was mainly in the residual fraction. The percentage of the soluble/exchangeable fraction of Zn, Mg, Mn were all above 10%, while that of Cu, Fe below 10%. The sum of the percentages of three fractions of mineral elements except Fe were all above 50%, and even beyond 90% for some elements. Therefore, it can be said that sewage sludges have higher nutritional value for plant growth, which is highly potential for agricultural development.