Phosphate Recovery From Digestate Using Magnesium-Modified Fungal Biochar

Abstract

Mg-rich biochars have been used for the removal and recovery of phosphate (PO43-) and ammonium (NH4+) from waste streams. In this study, a novel magnesium-modified biochar (Mg-FBC) was synthesized by immobilizing waste magnesite dust (WMD) into Aspergillus niger fungal biomass for the adsorption of PO(4)(3- )and NH4+. Pyrolysis at various temperatures and analysis using techniques such as SEM-EDS, TGA, XRD, FTIR, and BET revealed that biochar produced at 650 degrees C (Mg-FBC650) exhibited enhanced surface properties favorable for effective adsorption. This improvement is attributed to the increased surface area facilitated by the hyphal structure of A. Niger and the effective dispersion of MgO on its surface. In experiments using a synthetic phosphate solution, the adsorption capacity reached 595 mg PO43-/g BC, fitting the Langmuir model at pH 9. In addition, experiments with the liquid fraction of a real digestate (LFD) showed adsorption capacities of 502 mg PO43-/g BC and 150 mg NH4+/g BC, respectively. The adsorption mechanism was elucidated through SEM-EDS, XRD, and FTIR analyses confirming that Mg-FBC650 facilitates a multifaceted adsorption mechanism, including adsorption, electrostatic attraction, chemical precipitation, and surface complexation. Consequently, PO43- was the primary adsorbate in the synthetic solution, while both PO43- and NH4+ were effectively removed from the LFD, indicating that Mg-FBC650 has substantial potential as an efficient adsorbent for nutrient removal. As a result, Mg-FBC650 is believed to hold significant potential as a slow-release and readily transferable bio-fertilizer, particularly suitable for application in soils deficient in organic matter, nitrogen, and phosphorus. [GRAPHICS] .