Phosphorus adsorption by functionalized biochar: a review

Phosphorus is essential element for agricultural production, yet phosphorus ore resources are non-renewable and become depleted. Moreover, phosphate release from wastewater treatment plants and from inefficient crop fertilization induces pollution such as water eutrophication. Therefore, phosphorus recovery from wastewater is promising alternative source of agricultural phosphorus. Biochar can be used to adsorb phosphorus due to their porous structure, large surface area, abundant surface groups, and high mineral content of biochars. Biochar can be functionalized to improve their adsorption performance. Here, we review phosphorus recovery by functionalized biochar, with focus on biochar preparation and modification, factors influencing the efficiency of adsorption, adsorption mechanisms, and biochars as slow-release fertilizers. We discuss mechanisms for Mg-, Ca- and Fe-rich biochars.