Transformation of phosphorous during incineration of sewage sludge: Influence of steam and mineral

Sewage sludge (SS) incineration attracted massive attention due to its ability in decreasing SS volume and toxicity rapidly as well as recovering energy efficiently. The migration and transformation of phosphorous during SS incineration were studied through drop tube furnace. It was found that increasing temperature typically improved phosphorous recovery in ash. The effects of pyrolysis and combustion on phosphorous retention were mainly determined by calcium species in SS. CaCO3 in raw SS captured phosphorous during both pyrolysis and combustion, while CaSO3 had the capacity in capturing phosphorous only during pyrolysis. Total phosphorous (TP) enrichment ratio in ash was positively correlated with combustion temperature if calcium in SS was adequate. Introduction of 2% steam into combustion atmosphere helped minerals capture gaseous phosphorous a lot especially at 900 °C. However, further increase of steam in flue gas induced more phosphorous release during SS combustion. Adding 5% CaCO3, CaO or MgO all obviously improved the recovery of phosphorous at 1000 °C. 5% steam stimulated CaO for more phosphorous capture, but 10% steam hindered phosphorous capture. For CaCO3, 5–10% steam was a negative factor for phosphorous capture, while MgO captured phosphorous well with steam.