Phosphorus removal from dirty farmyard water by activated anaerobic-digestion-derived biochar

The management of anaerobic digestate is important to realize the value of the waste and enhance the whole system sustainability of anaerobic digestion. In this study, the phosphorus treatment of dirty irrigation water by biochar samples derived from digestate of anaerobic digestion were investigated. The biochars were further activated by steam activation with different duration time and KOH activation with different introducing ratios; the textural properties of biochars were optimized after activation from the aspect of biochar characterization. Notably, AD-N₂ demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g^–1. Besides the effect of biochar dosage on phosphorus removal, adsorption kinetics and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R² = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH⁰ = 17.93 kJ mol^–1) and spontaneous (ΔS = 96.24 J mol^–1 K^–1). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.