Valorization of salt post-modified poultry manure biochars for phosphorus recovery from aqueous solutions: investigations on adsorption properties and involved mechanism

In this research work, raw poultry manure biochar (RPM-B) was post-modified by two metal salts and then evaluated for P recovery from aqueous solutions in batch mode. The modified biochar characterization showed that RPM-B impregnation with aluminum and manganese salts led to a significant improvement of their surface properties through the pH-zero charge reduction as well as the specific surface areas and the functional group contents increase. Phosphorus recovery tests indicated that the post-treated biochar with AlCl3 (RPM-B-Al) and with KMnO4 (RPM-B-Mn) exhibited relatively high recovery efficiencies with Langmuir's adsorption capacities of 23.5 and 8.4 mg g(-1), respectively. Kinetics and isothermal data modeling, as well as the in-depth analytical characterization of the post-modified biochars before and after adsorption, indicates that P recovery occurs homogeneously on monolayer surfaces through mainly anion exchange, precipitation, and electrostatic interactions. On the other hand, P desorption efficiency increases with the desorbing solution pH values. The best P desorption yields were observed for an initial pH of 9.0 to 78% and 80% for RPM-B-Al-P and RPM-B-Mn-P, respectively. All these results suggest that RPM-B-Al and RPM-B-Mn could be considered promising materials for phosphorus recovery from wastewaters with a possible reuse in agriculture as potential soil amendments.

Automated summary

This research demonstrated that post-modifying biochar can significantly enhance its surface properties and phosphorus recovery efficiency. Phosphorus recovery mainly occurs homogeneously on monolayer surfaces through adsorption, precipitation, and electrostatic interactions, while desorption efficiency of phosphorus is influenced by solution pH values.