Kinetic Adsorption of Ammonium Nitrogen by Substrate Materials for Constructed Wetlands

Abstract

Constructed wetlands (CWs) are engineered systems that utilize natural systems including wetland vegetations, soils, and their associated microbial assemblages to assist in treating wastewater. The kinetic adsorption of ammonium nitrogen (NH + 4-N) by CW substrate materials such as blast furnace slag (BFS), zeolite, ceramsite, vermiculite, gravel, paddy soil, red soil, and turf, was investigated using batch experiments and kinetic adsorption isotherms. Both Freundlich and Lang-muir isotherms could adequately predict the NH + 4-N adsorption process. The maximum adsorption capacities of NH + 4-N, estimated from the Langmuir isotherm, ranked as: zeolite (33 333.33 mg kg −1) > turf (29 274.01 mg kg −1) > BFS (5 000 mg kg −1) > vermiculite (3 333.33 mg kg −1) > gravel (769.23 mg kg −1) > paddy soil (588.24 mg kg −1) > red soil (555.56 mg kg −1) > ceramsite (107.53 mg kg −1). Some properties of the substrate materials, including bulk density, specific gravity, hydraulic conductivity, uniformity coefficient ( K 60), curvature coefficient ( C c), organic matter, pH, exchangeable (or active) Cu, Fe, Zn and Mn, total Cu, and Fe, Mn, Zn, Cd, Pb and Ca, had negative correlations with NH + 4-N adsorption. Other properties of the substrate materials like particle diameter values of D 10, D 30 and D 60 (the diameters of particle sizes of a substrate material at which 10%, 30% and 60%, respectively, of the particles pass through the sieve based on the accumulative frequency), cation exchange capacity (CEC), exchangeable (or active) Ca and Mg, and total K and Mg had positive correlations with NH + 4-N adsorption. In addition, active K and Na as well as the total Na had significant positive correlations with NH + 4-N adsorption. This information would be useful for selection of suitable substrate materials for CWs.