Abstract
Water treatment sludge from algal blooms were analyzed and compared with general water treatment sludge as the pyrolysis temperature was varied from 300 °C to 900° C. Elemental analysis showed that the water treatment sludge in the eutrophication region has ~12% carbon content, higher than that (8.75%) of general water treatment sludge. X-ray diffraction (XRD) analysis of both types of sludge showed that amorphous silica changed to quartz and weak crystalline structures like kaolinite or montmorillonite were decomposed and changed into stronger crystalline forms like albite. Fourier transform infrared spectroscopy (FT-IR) peaks of humic/fulvic acid that indicated the affinity to combine with heavy metals disappeared above 700 °C. Toxicity characteristic leaching procedure (TCLP), conducted to determine the heavy metal leaching amount of pyrolyzed water treatment sludge, showed the lowest value of 5.7 mg/kg at 500 °C when the humic acid was not decomposed. At 500 °C, the heavy metal leaching ratio to the heavy metal content of high organic content water treatment sludge and low organic content water treatment sludge were 1.87% and 3.19%, respectively, and the water treatment sludge of higher organic content was more stable. In other words, pyrolysis of water treatment sludge with high organic content at 500 °C increases the inorganic matter crystallinity and heavy metal leaching stability.
Highlights
The increasing global population and expansion of industry have increased water usage and water pollution
Because sewage sludge which has higher heavy metal concentrations and a higher organic content than water treatment sludge, can be recycled as biochar for soil application through pyrolysis, we suggest that pyrolysis can be applied to water treatment sludge with lower heavy metal concentrations as a valuable recycling method
The results of this study demonstrate that there is a good possibility of recycling high organic content water treatment sludge
Summary
The increasing global population and expansion of industry have increased water usage and water pollution. Three methods have attracted attention as potential alternatives: the recycling of coagulants contained in large quantities in sludge using acid treatment, the utilization of sludge in earthworks; for example, in cement mix, and the application of sludge for soil modification such as soil pH adjustment [4]. These recycling methods utilize the specific features of water treatment sludge; i.e., low organic content and high inorganic content [7] Water treatment sludge was treated through landfilling [3,4], but new treatment alternatives are required due to the limitations of landfill sites and the pollution of soil and underground water caused by heavy metals, as well as iron and aluminum salts in the sludge [5,6].
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