607 / 2019-01-19 21:25:04

Potential Recovery of Phosphorus during the Fluidized Bed Incineration of Sewage Sludge

sewage sludge ash, phosphorus recovery; apatite phosphorus, non-apatite inorganic phosphorus, heavy metals

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Abstract: Phosphorus is a limited non-renewable resource that is indispensable as an essential nutrient for the growth of organisms in most ecosystems. To demonstrate the reuse of phosphorus resources from sewage sludge ash (SSA), experiments were conducted in a circulating fluidized bed kiln. The experimental results demonstrated that high temperature and calcium oxide (CaO) were beneficial for the transformation of non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP). Thermogravimetric differential scanning calorimetry analysis (DSC-TG)was combined with X-ray diffraction measurements (XRD) to simulate the process of sewage sludge incineration of the crystal phase transition between aluminium phosphate (AlPO4) and CaO, forming stable AP (Ca2P2O7, CaHPO4 and Ca3(PO4)2) in the temperature range of 675 to 850 癈. Additionally, 89.29% of the phosphorus was enriched in sewage sludge bottom ash and 5.61% was distributed in fly ash, with AP being the primary component in the fly ash at 850 癈. XRD results indicated that the main phosphate minerals in bottom ash were calcium magnesium phosphate (Mg3Ca3(PO4)4) and calcium phosphate (Ca3(PO4)2) which were high bio-availability. AP content generally increased with decreasing particle size, whereas NAIP content exhibited the opposite tendency, and became stable when the particle size was less than 37.5 祄. Risk index results implied that the heavy metals in the phosphorus-enriched SSA have low potential ecological risk. Thermodynamic equilibrium calculations revealed that P reacted with the other metal ions was in the following order: Ca2+>Mg2+>Al3+>Fe3+
KEYWORDS: sewage sludge ash, phosphorus recovery; apatite phosphorus, non-apatite inorganic phosphorus, heavy metals