Transformation of heavy metal speciation during sludge drying: mechanistic insights.

Speciation can fundamentally affect on the stability and toxicity of heavy metals in sludge from wastewater treatment plants. This research investigated the speciation of heavy metals in sludge from both municipal and industrial sources, and metal speciation change as a result of drying process to reduce sludge volume. The changes in sludge properties including sludge moisture content, temperature, density, and electrical conductivity were also monitored to provide insights into the mechanisms causing the change in heavy metal speciation. The results show that the drying process generally stabilized Cr, Cu, Cd, and Pb in sludge by transforming acid-soluble, reducible, and oxidizable species into structurally stable forms. Such transformation and stabilization occurred regardless of the sludge source and type, and were primarily caused by the changes in sludge properties associated with decomposition of organic matter and sulfide. The results enhanced our understanding of the geochemical behavior of heavy metals in municipal sludge, and are useful for designing a treatment system for environment-friendly disposal of sludge.

[Quantitative partitioning of soil selenium in the selenium-rich area of Northern Zhejiang Plain].

To clarify the contribution of different component of selenium is the basis for evaluation of the sustainable development and utilization of selenium-rich soil. Xiuzhou district, where the soil is rich in selenium, was chosen as the study area, and its soil selenium content was qualitatively separated as the natural background component and the exogenous component through cross-validation of integrated geo-analysis and multivariate statistics. Subsequently, the contribution rate of the different component of the selenium content was separated quantitatively using frequency distribution functions. The results showed that the natural background component accounted for 90% in the soil selenium content and the exogenous component accounted for 10%, which indicated that the land sources rich in selenium in Xiuzhou district has the potential for sustainable development and utilization.

[Drying characteristics and apparent change of sludge granules during drying].

Three different weight grades of sludge granules (2.5, 5, 10 g) were dried at constant temperature of 100, 200, 300, 400 and 500 degrees C, respectively. Then characteristics of weight loss and change of apparent form during sludge drying were analyzed. Results showed that there were three stages during sludge drying at 100-200 degrees C: acceleration phase, constant-rate phase, and falling-rate phase. At 300-500 degrees C, there were no constant-rate phase, but due to lots of cracks generated at sludge surface, average drying rates were still high. There was a quadratic nonlinear relationship between average drying rate and drying temperature. At 100-200 degrees C, drying processes of different weight grade sludge granules were similar. At 300-500 degrees C, drying processes of same weight grade of sludge granules were similar. Little organic matter decomposed till sludge burning at 100-300 degrees C, while some organic matter began to decompose at the beginning of sludge drying at 400-500 degrees C.