A comparative study on phosphate removal from water using Phragmites australis biochars loaded with different metal oxides.

Pengfei Wang,Shuhang Wang,Guannan Cui,Zhaosheng Chu,Mengmeng Zhi

doi:10.1098/rsos.201789

Abstract

Metal oxide-loaded biochars are a promising material to remove phosphate from polluted water to ultra-low concentrations. To facilitate preparing the metal oxide-loaded biochar with the best phosphate adsorption performance, five biochars loaded with Al, Ca, Fe, La and Mg oxides, respectively (Al-BC, Ca-BC, Fe-BC, La-BC and Mg-BC) were produced using Phragmites australis pretreated with 0.1 mol AlCl3, CaCl2, FeCl3, LaCl3 and MgCl2, respectively, characterized, and phosphate adsorption kinetics and isotherms of the biochars were determined. The maximum phosphate adsorption capacities (Qm) of the biochars ranked as Al-BC (219.87 mg g−1) > Mg-BC (112.45 mg g−1) > Ca-BC (81.46 mg g−1) > Fe-BC (46.61 mg g−1) > La-BC (38.93 mg g−1). The time to reach the adsorption equilibrium ranked as La-BC (1 h) < Ca-BC (12 h) < Mg-BC (24 h) = Fe-BC (24 h) <Al-BC (greater than 72 h). Qm of Ca-BC, Fe-BC, La-BC and Mg-BC depend on the molar content of metals in the biochars. The small phosphate adsorption rate of Al-BC is due to the slow intra-particle diffusion of phosphate attributed to the undeveloped porosity and dispersed distribution of AlOOH crystals on the Al-BC surface. Mg-BC is suggested for phosphate removal from water considering adsorption rate and capacity. Al-BC is applicable when a long contact time is allowed, e.g. as a capping material to immobilize phosphate in lake sediments.

Highlights

In order to control the eutrophication of aquatic ecosystems, tremendous efforts have been made in wastewater treatment plants (WWTPs) to remove phosphorus (P)
The metal chlorides decomposed into metal oxides which were impregnated in the biochar matrix and hydrogen chloride which was volatilized [29]
The linear correlation between the maximum phosphate adsorption capacities of the biochars loaded with Ca, Fe, La and Mg oxides, respectively, and the molar contents of these metals in the biochars found in this study indicates that the Ca, Fe, La and Mg chlorides are substitutional to be used to prepare the metal oxide-loaded biochars regarding the phosphate adsorption capacity

Summary

Introduction

In order to control the eutrophication of aquatic ecosystems, tremendous efforts have been made in wastewater treatment plants (WWTPs) to remove phosphorus (P). The total P concentration in the effluent of municipal WWTPs should not exceed the strictest limit of 0.5 mg l−1 in China (GB18918-2002) and 1.0 mg l−1 in Europe (Council Directive 91/271/EEC). The eutrophication of the receiving water bodies may be aggravated even if the discharge limit is met, especially when the dilution effect of the receiving water body is low [1]. More strict discharge limits (0.01–0.1 mg l−1) are or will be applied [2]. Purification of polluted water from non-point sources such as agricultural runoff and stormwater overflows has drawn increasing attention since P input from these non-point sources becomes important after the strict discharge limits have been met in WWTPs [3]. It is necessary to develop efficient and cost-effective P removal technologies to treat such polluted water with a low P concentration. Adsorption is a suitable technology for such purposes and has the advantages of simple design, easy operation and cost-effectiveness [4]

Methods

Results

Conclusion