Dynamic model extension for the design of full-scale artificial free superficial flow wetland systems

Addressing the low total nitrogen removal percentages observed during the sewage treatment in free superficial flow wetland systems is crucial to the design of full-scale facilities. A well-controlled pilot-scale experiment with two parallel shallow basins, one planted with Typha latifolia and the other without, enabled the development of a mathematical model, following the activated sludge model framework. The pilot unit was operated so as to achieve both organic matter and nitrogen removal. The key processes accounted for were ammonification, heterotrophic growth, nitrification, algal growth and plant transpiration. The dynamic model developed predicts the plant mass and evapotranspiration rate throughout the year. The predictive ability of the model was tested with a free water surface constructed wetland serving a population of 400, with the sole modification being the need to account for oxygen limitation in the rate of nitrification. The required inputs include the inflow characteristics and rainfall and air temperature climatic data, directly influencing the plant evapotranspiration rate. The seasonal dependence of the water temperature was determined through an energy balance.