Optimisation of phosphorus recovery process from biogas slurry using straw-derived biochar coupled with Mg/La oxide as an adsorbent

Phosphorus recovery from biogas slurry can realize the management and utilization of nutrients. Phosphorus adsorption has been hindered by multiple issues, including the incompatibility of biogas slurry and the lack of phosphorus recovery research. Therefore, the key influencing factors and adsorption mechanisms of phosphorus recovery should be analysed to effectively use biogas slurry resources. In this study, a new adsorbent of straw-derived biochar coupled with Mg/La oxides (6YBC-LDO) was used as an adsorption column filler. The effects of adsorption column height, biogas slurry concentration and flow velocity on phosphorus recovery were also studied via the response surface method (RSM). The results showed that when the mass concentration, flow rate, and column height of biogas slurry were 106.24 mg/L, 2.44 mL/min, and 1.60 cm, respectively, the recovery efficiency of phosphorus was higher, and the equilibrium adsorption capacity (qequ.) could reach 287.58 mg/g. The optimised process could further improve the regeneration rate and life cycle of 6YBC-LDO. Correlation analysis of phosphorus recovery efficiency and the characteristics of biogas slurry showed that high chemical oxygen demand (COD) and total solids (TS) content have a positive correlation with the phosphorus concentration of biogas slurry. High solid content may hinder the flow rate of biogas slurry, which directly and indirectly affects the phosphorus recovery efficiency, and the results provide a scientific basis for regulating phosphorus recovery in biogas slurry.