Efficient Phosphate Removal from Wastewater by Ca-Laden Biochar Composites Prepared from Eggshell and Peanut Shells: A Comparison of Methods

Abstract

Biochar is currently widely used as the adsorbent for phosphorus (P) removal from wastewater. Cheap and green modified materials and efficient preparation methods are the key to obtain efficient and economical engineering biochar. Conventional salt solution and chemical impregnation are common methods for preparing engineered biochar. However, this preparation method is not environmentally friendly or cheap due to the price of salt solutions and the solvent treatment process for chemical impregnation. In this article, Ca-laden biochar was prepared using peanut shells as carbon base materials and discarded eggshells as calcium source. Two methods (ball milling and chemical impregnation) of building the Ca-laden biochar were compared from the perspective of the characterization of biochar, the adsorption performance and the economic cost. The composition and structure of biochar were analyzed by the element content, functional group, X-ray diffraction, energy spectrum and electron microscope scanning etc. The adsorption behavior of biochar was tested in different environments (pH and temperature). The results revealed that the capacity of P adsorption by the Ca-modified biochar was higher than the adsorption by raw biochar, and that the prepared Ca-laden biochar has a wide working environment. Moreover, the Ca-laden biochar prepared by ball milling has a higher specific surface area and more porosity. The Ca-modified biochar through ball milling has a higher amount of adsorbed P than that of through chemical impregnation. This work not only creates a novel method for making excellent P adsorbents, but also offers an environmentally friendly use for agricultural eggshells and peanut shells.