Lihua Cui

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.

Phosphorus Sorption Capacities and Physicochemical Properties of Nine Substrate Materials for Constructed Wetland

Constructed wetland (CW) is a promising technique for removal of pollutants from wastewater and agricultural runoff. The performance of a CW to remove pollutants, however, hinges on the use of suitable substrate materials. This study examined the physicochemical properties and phosphorus (P) sorption capacities of nine different CW substrate materials using both batch experiments and the Freundlich as well as the Langmuir isotherm. The nine substrate materials used in this study were turf, topsoil, gravel, midsized sand (MSS), blast furnace slag (BFS), coal burn slag (CBS), blast furnace artificial slag (BFAS), coal burn artificial slag (CBAS), and midsized artificial sand (MSAS). Experimental data showed that sorption of P increased with initial solution P concentrations for all nine substrate materials. The maximum P sorption capacity of the substrate materials estimated by Langmuir isotherm was in the following order: turf (4243 mg/kg substrate) > BFAS (2116 mg/kg substrate) > BFS (1598 mg/kg substrate) > CBS (1449 mg/kg substrate) > top soil (1396 mg/kg substrate) > CBAS (1194 mg/kg substrate) > MSAS (519 mg/kg substrate) > gravel (494 mg/kg substrate) > MSS (403 mg/kg substrate). The specific gravity of eight substrate materials (except gravel) had very significant negative correlations with the P sorption, whereas the particle diameter of D60 and uniformity coefficient (K60) had positive correlations with the P sorption. The cation exchange capacity, organic matter, available ferrous, and exchangeable aluminum of the eight substrate materials also had very significant positive correlations with the P sorption, while the pH of the substrate materials showed a very significant negative correlation with the P sorption. Our study further suggests that turf and CBAS are the two relatively ideal substrate materials suitable for removal of P from a CW system.