Kinetics of Ammonium, Nitrate and Phosphate Uptake by Candidate Plants Used in Constructed Wetlands

Abstract

Abstract The constructed/artificial wetland system is a new sewage technique with low cost and less energy consumption for removal of nitrogen and phosphorus in wastewater, and the wetland plants have the important functions in the system. In wastewater purification, plants can absorb and utilize the nutrients (nitrogen and phosphorus) directly, and enhance nutrient transformation processes such as nitrification, denitrification, adsorption and desorption. In this study, a series of experiments for investigating the kinetics of ammonium, nitrate and phosphate uptake by 8 candidate wetland plants, such as Carex taliensis Franch, Dracaena sanderiana Virens, Impatiens balsamina, rush (Juncus effusus L.), mulberry (Morus indica L.), wetland rice (Oriza Sativa L.), Salvia plebeia R. Br., and Sesbania cannabina Poir, were carried out under controlled conditions (temperature 25-28, illumination 3000Lux, relative°C humidity 60-70%). The results indicated that the kinetic characteristics of ammonium, nitrate and phosphate uptake by the selected plants could be well illustrated with the Michaelis-Menten equation, and the kinetic parameters (maximum rate and Km value of absorption) could also be calculated using the regression equations. The orders of maximum uptake rate were as follows: Morus indica L. > Carex taliensis Franch > Oriza Sativa L. > Impatiens balsamina > Juncus effusus L. > Sesbania cannabina Poir > Salvia plebeia R. Br. > Dracaena sanderiana for ammonium; Carex taliensis Franch > Oriza Sativa L. > Sesbania cannabina Poir > Juncus effusus L. > Impatiens balsamina > Morus indica L. > Salvia plebeia R. Br. > Dracaena sanderiana for nitrate; Oriza Sativa L. > Juncus effusus L. > Salvia plebeia R. Br. > Dracaena sanderiana > Impatiens balsamina > Morus indica L. Sesbania cannabina Poir > Carex taliensis Franch for phosphate. Sesbania cannabina Poir., Dracaena sanderiana Virens and Salvia plebeia R. Br. had the smallest Km value for ammonium uptake, and Impatiens balsamina, Dracaena sanderiana Virens and Salvia plebeia R. Br. had the smallest Km value for nitrate uptake, Sesbania cannabina Poir., mulberry and Dracaena sanderiana Virens had the smallest Km value for phosphate uptake. According to the kinetic characteristics of N and P uptake, we suggested that plant species with higher maximum uptake rates could be used in the first section for cleaning up wastewater with high nutrient concentrations, and plant species with lower Km values could be used in subsequent sections for cleaning up wastewater with lower nutrient concentrations.