Simulation of organics and nitrogen removal from wastewater inconstructed wetland

Modelling wastewater treatment processes is an effective tool for prediction and analysis of treatment system performance. In this study, removal of organics and nitrogen compounds of municipal wastewater is simulated in a constructed wetland based on system dynamic approach using Stella software. In the developed model, organics are represented by BOD and nitrogen compounds including nitrate, ammonia and organic nitrogen. Removal mechanisms for BOD include microbial degradation, plant absorption, and sedimentation. The mechanisms for nitrogen removal are denitrification, sedimentation and plant absorption. The model was calibrated and validated for a horizontal subsurface flow wetland in Arundel mills, Maryland based on 24 data gathered biweekly during one year. An acceptable R and Nash– Sutcliffe coefficient of efficiency between the simulated and observed concentration values were obtained which provides a reliable tool in operation and management of the specified wetland in this case study. Based on the results of the model, overall BOD removal consists of 43% for the share of microbial degradation, 27% plant absorption and 30% for sedimentation. Also from the overall nitrogen removal, the share of sedimentation for organic nitrogen is 22%, plant absorption 14% and denitrification is 45%. According to the results, the developed model can be efficiently used in prediction, design and operation of constructed wetland.