System dynamic modeling of uptake rate of nitrogen by plant in subsurface constructed wetlands

Abstract

Constructed wetlands have great ability for nitrogen removal from wastewater. The common removal process for nutrients in constructed wetlands through a biological means is plant uptake; yet, research works on plant contribution to pollutants removal are limited. This research paper is centered on development of simulation model for the absorption rate of nitrogen by plants in a horizontal sub surface flow constructed wetland receiving septic tank effluent. Wetland characteristics, plant characteristics and nitrogen transformation processes were addressed in the model using STELLA 9.1.3 as a means for graphical formulation. Field measurement and laboratory analyses were conducted. The results of the study indicate that uptake rate of NH₄-N is within the range of 0.0075 and 0.0150 mg/kg.day while that of NO₃-N range from 9.326e-6 to1.712e-3 mg/kg.day. The simulated results were in accordance with the trends in literature. The data from model runs show that increase in nitrogen demand made a significant change in plant uptake rate while the variation in other parameters caused little or no change on plant uptake rate. This is an indication that uptake rate of nitrogen in wetland strongly depends on the vegetation type considered for a constructed wetland. Understanding the quantitative representation of the separation mechanisms is required for proper management of wetland.