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During sewage treatment, phosphorus (P) is concentrated in sewage sludge, and the sludge is incinerated to produce P-concentrated ash particles. The P-containing ash particles possess high adhesiveness at high temperatures, which can cause problems for the incineration plants. Phosphorus is considered a key element for inducing ash particles adhesiveness; however, the mechanistic details remain unclear. The present study clarified the role of P in particle adhesion at high temperatures using synthetic ashes, which consist of P and Si. The tensile strength of synthetic ash powder beds was quantified using a specially developed device that could estimate adhesiveness of particles at high temperatures. Since synthetic ash has few components compared to incineration ashes collected from commercial incineration plants, evaluating the role of P is easier. Iron (Fe)-containing chemical species are used for water treatment as chemical conditioners, and Fe also is concentrated with P in the sludge-incinerated ashes. To determine the interactions between Fe and P, iron oxide nanoparticles were added to P-containing synthetic ashes and their adhesiveness was evaluated. A small addition of iron oxide nanoparticles significantly decreased the adhesiveness of P-containing synthetic ashes at high temperatures, information that can help to control adhesiveness of sewage sludge-incinerated ashes.

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