Phosphate adsorption/desorption kinetics and P bioavailability of Mg-biochar from ground coffee waste

Ground coffee waste (GCW) was pyrolyzed to produce impregnated Mg biochar (Mg-biochar) for the recovery of phosphorus from wastewater. Adsorption of phosphate (1 mM) followed 1st order kinetics to give kinetic coefficient (k1) of 0.12 L/h and adsorption equilibrium (qe) of 14.33 mg P/g biochar. Maximum phosphate adsorption reached 56 mg P/g biochar. XRD and FT-IR showed that phosphates were bound to the Mg-biochar not only by electrostatic adsorption but also by covalent bonds to form magnesium phosphate crystal, Mg3(PO4)2. P desorption and bioavailability of saturated Mg-biochar favored acidic condition and the result indicates that phosphate-saturated GCW Mg-biochar could be utilized as an effective and eco-friendly P adsorbent and fertilizer.