Transformation of Phosphorus during Low-Temperature Co-Combustion of Sewage Sludge with Biowastes
Xiangdong Meng, Qian Wang, Biao Wan, Jie Xu, Qunxing Huang, Jianhua Yan, Yuanzhi Tang
Abstract
Thermal treatments of phosphorus (P)-rich sewage sludge for efficient P reclamation have recently gained much attention. Our recent research proposed a low-temperature combustion method that can simultaneously target safe waste disposal, fly ash volume reduction, heavy-metal stabilization, P recovery, and energy reuse. To further optimize treatment conditions and gain deeper insights into P speciation, this study systematically characterized P transformation during low-temperature co-combustion of sewage sludge with biowaste by combining X-ray absorption spectroscopy, sequential extraction, and nuclear magnetic resonance spectroscopy analyses. Organic P, phytic acid, and pyrophosphate in the raw feedstock transformed into orthophosphate during low-temperature combustion. With increasing mass fraction of biowaste, low-temperature co-combustion increased the relative abundance of Ca-associated P and decreased the abundance of Fe-associated P. The dominant P species in the produced bottom ash is strongly correlated to the amount and speciation of metals in the feedstock and their affinities to P. The introduction of biowaste altered the enrichment efficiency and availability of P in the ash. The results from this study revealed the effects of combustion conditions and feedstock characteristics on P speciation and provided a fundamental basis for guiding the optimization of the thermal treatment method for eliminating hazardous wastes, reusing energy, and improving P reclamation efficiency.