<p>Biogas slurry was rich in phosphorus and serves as an important source for phosphorus recovery. Generally, the soluble orthophosphate (Ortho-P) was the main form of phosphorus recovered by adsorbents, however, the proportion of dissolved orthophosphate (Ortho-P) is less than 30% of TP. Therefore, promoting the transformation of other phosphorus forms to Ortho-P is extremely crucial for improving the recovery efficiency of phosphorus in biogas slurry. In this study, H₂SO₄ was used for the acidification pretreatment of biogas slurry to improve the efficiency of phosphorus recovery. The effects of different acidification conditions on the transformation of phosphorus forms and physicochemical properties of biogas slurry as well as the phosphorus recovery effect of the straw biochar magnesium–lanthanum hydrotalcite composite material (6YBC-LDO) were investigated. When H₂SO₄ was added to adjust the pH of the biogas slurry to 6.0, 6.5, and 7.0, the mass concentration of Ortho-P increased by a factor of 20, 9, and 4, respectively, compared with the original biogas slurry. The total phosphorus recovery capacity of 6YBC-LDO from acidified biogas slurry at pH 6.0, 6.5, and 7.0 were 150.99, 144.73, and 40.32&#xa0;mg/g, respectively, with phosphorus recovery rates of 64%, 85%, and 99%, respectively. The phosphorus recovery products from biogas slurry treated with pH 7 were mainly phosphate complexes with higher purity. High purity phosphorus recovery materials could be used as for efficient phosphorus fertilizers production in the future, which has profit of 4.44 RMB with treatment 1 m³ biogas slurry.</p>