Phosphorus removal from aqueous solution by adsorption using wetland-based biochar: Batch experiment

Abstract

This article experiments wetland-based biochar as an effective adsorbent for phosphorus removal. In this experiment, four common wetland plants, canna (C), umbrella palm (U), bamboo reed (B), and Thalia dealbata (T), were used as the main raw materials. Twelve kinds of biochar (C300, C500, C700, U300, U500, U700, B300, B500, B700, T300, T500, and T700) were obtained at three pyrolysis temperatures (300°C, 500°C, and 700°C). The results show that canna (C) and umbrella palm (U) are more suitable as raw materials for phosphorus removal using biochar. If bamboo reed (B) and Thalia dealbata (T) are used as raw materials for phosphorus removal using biochar, there is a greater risk of phosphorus release. With the increase of pyrolysis temperature (700°C > 500°C > 300°C), there is an increasing trend of phosphorus adsorption effect. The theoretical maximum adsorption capacity of C700, U700, and C500 was 39.24, 7.08, and 7.26 mg P·g-1 at an initial concentration of 50 mg·L-1 phosphorus, respectively. The theoretical adsorption capacity of C700 (Q max = 39.24 mg P·g-1) was much higher than that of the general modified adsorption materials. It also has a larger tolerance range to pH (3-11). The results of kinetic model fitting showed that the adsorption mechanism of C700, U700, and C500 on phosphorus can be better simulated by intra-particle diffusion and Elovich model, and the adsorption mechanism includes surface adsorption and intra-particle diffusion. The fitting of isothermal adsorption model showed that Langmuir-Freundlich equation is more suitable for the description of adsorption characteristics of C700, U700, and C500, and the fitting coefficient R 2 is 0.9928, 0.9949, and 0.9897, respectively. It indicates that the adsorption of phosphorus on C700, U700, and C500 has a balance of uniform and nonuniform surface, and monolayer and multilayer adsorption could occur. The results from this work demonstrated that the biochar obtained from canna at 700°C has good adsorption and phosphorus removal potential without modification, and it can be used as the preferred biochar for phosphorus removal of high concentration with large pH changes. In the final validation experiment, the phosphorus removal rate of C700 was up to 77.4% on the treatment of actual phosphorus containing wastewater.