<p>Phosphorus depletion is a critical global scale. Sewage sludge incineration ash (SSIA) offers a sustainable alternative to non-renewable phosphate rock. This study explored the phosphorus distribution in sewage sludge and biomass/coal co-incineration ash, and assessed the efficiency of phosphorus extraction by various acids. Total phosphorus (TP) in SSIA was about 38.3&#xa0;mg/g, while it ranged from 35.0 to 47.1&#xa0;mg/g in co-incineration ash, mainly in the form of inorganic phosphorus (IP). Co-incineration converted non-apatite phosphorus (NAIP) to apatite phosphorus (AP), primarily due to the reduced sulfur content and increased alkaline earth metal content. Phosphorus extraction efficiency followed this order: H₂SO₄ &gt; HCl &gt; H₂C₂O₄ &gt; HAc. A mathematical model using Response Surface Methodology (RSM) was developed to predict the effectiveness of H₂SO₄ for wet extraction of co-incineration ash. Results showed that in 90% sludge and 10% biomass co-incineration ash (90SBIA), the interaction between the H/P molar ratio and leaching time was significant, while the liquid-to-solid (L/S) ratio had minimal effect on extraction efficiency. In contrast, in 90% sludge and 10% coal co-incineration ash (90SCIA), the interaction between the L/S ratio and leaching time was more pronounced, and leaching time had a lesser effect on extraction efficiency. Further analysis revealed that the acid consumption cost for extracting equivalent phosphorus was higher for 90SCIA than for 90BIA, with a 41.5% increase in cost. Overall, sewage sludge and biomass co-incineration ash is a promising source for phosphorus recovery, aiding future extraction and production of phosphorus-containing products.</p> Graphical Abstract <p></p>