Recovery of phosphorus from sewage sludge incineration ashes

Urban sewage sludges are incinerated at an incineration and energy recovery plant of BUSKİ in Bursa. The gasses that are generated from combustion in the plant are removed by bag filter and multi-cyclone units. Sewage sludge ashes with high phosphorus contents of 17.36% (bag filter ashes) and 11.49% (multi-cyclone ashes) draw attention as a source of P2O5. The aim of this study is to investigate the evaluation of ashes from bag filter and multi-cyclone in phosphorus recovery. For this purpose, chemical composition, morphological structures, phase analysis of sewage sludge ashes were examined. This study investigated phosphorus recovery using chemical extraction by oxalic acid, citric acid, sulphuric acid and nitric acid. Phosphorus extraction was investigated at different concentrations. Ashes were mixed with acids at a solid to liquid ratio of 20 ml/mg-1 for 2 hours. The extracted phosphorus was measured colorimetrically and analyses for heavy metals were measured by ICP-OES. The residues analyzed with XRD, SEM-EDS, ICP-OES. The extracted phosphorus amount range of is 0.01-91.42 mg/g in bag filter ash and 0.01-59.82 mg/g in multi-cyclone ash. When oxalic acid is used in the highest phosphorus bag filter ash extracted, it was 91.42 mg/g. The phosphorus recovery potential of bag filter ash is higher than multi-cyclone ash. Acid extraction resulted in the dissolution of both phosphorus and heavy metals in ash. Therefore the limit values in the regulation were exceeded. Bag filter ash and multi-cyclone ash can be an alternative to phosphate rock in fertilizer production providing that removal of heavy metal.