Transformation of Phosphorus during Low-Temperature Co-Combustion of Sewage Sludge with Biowastes

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.

Phosphorus recovery from wastewater and bio-based waste: an overview

“…These results from the polymerization into more condensed phosphates. This tendency of utilizing a low temperature was confirmed in the work of Meng et al (2021), wherein the co-combustion process (<600°C) the degree of non-digestible forms of Fe, Al phosphates to Ca forms was elevated [ 166 ]. However, this method can only be used on sewage sludge with a low heavy metal content and without the chemically recovered phosphorus.…”

Effect of Prestage Hydrothermal Treatment on the Formation of Struvite vs Vivianite during Semicontinuous Anaerobic Digestion of Sewage Sludge

“…As Mg, Fe, Al, and/or Ca are major metals present in raw sludges, phosphate could either precipitate with these metals or adsorb on their metal mineral phases. Thus, a set of P standard compounds were used for LCF analysis, including (1) phytic acid (PhyAc), representing organic phosphate; (2) struvite, MgHPO 4 , and Mg 3 (PO 4 ) 2 , representing Mg-associated P; (3) vivianite, strengite (FePO 4 ·2H 2 O), and phosphate-adsorbed ferrihydrite (P-Ferrihy), representing Fe-associated P; (4) AlPO 4 and phosphate sorbed on Al 2 O 3 (P–Al 2 O 3 ), representing Al-associated P; and (5) brushite, hydroxyapatite (HAP), amorphous calcium phosphate (ACP), and octacalcium phosphate (OCP), representing Ca-associated P. These standard compounds used in this study have been shown to well represent P species in sludge samples. ,,− Details on these standard compounds were presented in Table S1 and Figure S1.…”

Review of Phosphorus Chemistry in the Thermal Conversion of Biomass: Progress and Perspectives

“…X-ray absorption spectroscopy (XAS) was also used to characterize association of phosphorus in biomass, − biochar, ,, and ash. − In Figure d, spectra of the X-ray absorption near edge structure (XANES) of poultry litter, reported by Shober at al., is shown. Normally the spectrum is interpreted by using reference spectra of model compounds.…”