Comparison of Phosphorus Extraction from Sludge Incinerated Bottom Ash and Sludge Incinerated Fly Ash Using Sulfuric Acid

Abstract

Ashes from excess sludge incineration plants contain a high content of phosphorous (P). Taking H 2 SO 4 as an extraction agent, this study investigated the P recovery potential of sludge incinerated bottom ash (SIBA) and sludge incinerated fly ash (SIFA) from an incineration plant in China. The results showed that P contents of SIBA and SIFA were 70,200 and 9,100 mg/kg, respectively, which indicated that SIBA had greater recycling potential of P. The reaction temperature played a significant role in P extraction process. The extraction yields were 99% and 98% from SIBA and SIFA at 45°C, and it also demonstrated that raising the temperature could extract P almost entirely from both SIBA and SIFA. Considering the cost-effective consumption, P extraction yields obtained from SIBA and SIFA were 89% and 90% under the optimized conditions (reaction time of 30 min, H 2 SO 4 dosage of 12 mmol, the reaction temperature of 25°C, and a ratio of leachate/solid ash of 35). The contents of Cu, Zn, Pb, Cr, and Ni in the leaching solution from SIBA and SIFA met the requirements of U.S. AAPFCO and Chinese national regulatory of P fertilizer production. Based on an approximate estimate, a total of 6.27 kg of P would be extracted from 1,000 kg of sludge (about 6.25 kg of P was extracted from SIBA and 0.02 kg of P was extracted from SIFA). It would provide a reference for the recovery of P from sludge incinerated ash worldwide.

Activated Carbon and P-Rich Fertilizer Production from Industrial Sludge by Application of an Integrated Thermo-Chemical Treatment

“…To the best of the authors' knowledge, many studies are available concerning the extraction of phosphorus from sludge ash [33][34][35] or the production of biochar by slow pyrolysis [36,37]. However, limited literature was found addressing the simultaneous valorization of both carbon and phosphorus retained in sewage sludge, mainly involving hydrothermal carbonization as a thermochemical treatment process [38,39], characterized by high volatility and low market value.…”