QUANTIFY FLUORINE TRANSFORMATION IN PFCS DURING THE THERMAL TREATMENTS OF LIME-CONDITIONED SEWAGE SLUDGE

摘要

Studies have shown that wastewater treatment sludge is a sink for environmental perfluorochemicals (PFCs). Thermal treatment (such as incineration) is one of solid waste management strategies and can offer a very effective mechanism to break the robust halogen-carbon bonds in PFCs. PFOS can be thermally decomposed at temperatures above 600?C, and tetrafluoromethane (CF4) and hexafluoroethane (C2F6) were the main final products. However, CF4 and C2F6 compounds were found to be potent greenhouse gases. In this study, quantitative X-ray diffraction (QXRD) technique was used to analyze the fate and transformation of fluorine in PFOS during the thermal treatment of lime-conditioned sewage sludge. Two fluorine mineralization mechanisms were found to form CaF2 (calcium fluoride) and Ca5(PO4)3F (fluorapatite) in the thermally treated products. Between 300?C and 600?C, calcium fluoride was found to dominate in the thermally treated products. At higher temperatures (700?C to 900?C), increases in the treatment time and temperature had an adverse effect on the overall fluorine crystallization efficiency. The analysis also shows that when treating sludge with low PFC content at high temperatures, the formation of fluorapatite may be the primary mechanism for mineralizing the fluorine in PFCs.