Land-Based Wastewater Treatment System Modeling Using HYDRUS CW2D to Simulate the Fate, Transport, and Transformation of Soil Contaminants: Fid-Bau Portal

Land-Based Wastewater Treatment System Modeling Using HYDRUS CW2D to Simulate the Fate, Transport, and Transformation of Soil Contaminants

Dong, Younsuk / Safferman, Steven I. / Nejadhashemi, A. Pouyan

Abstract

Land-based wastewater treatment systems (onsite or decentralized) have been used for many years because of their low cost, energy use, and maintenance requirements compared to conventional wastewater treatment systems. Performance depends on the hydraulic and organic wastewater loadings, soil characteristics, and soil conditions. Although many factors impact performance, design criteria are generally based on empirical relationships, which do not adequately consider site- and waste-specific conditions. To improve a system’s design and more accurately evaluate performance, a physical-based model was utilized to simulate a complex land application wastewater treatment system. HYDRUS Constructed Wetland 2D (HYDRUS CW2D) simulates the movement of water and multiple solutes in soil. The model was originally designed to simulate wastewater treatment in wetlands but was calibrated and validated in this research for land-based wastewater treatment systems. To calibrate and validate the model, laboratory bench-scale drain field (trench) experiments were conducted. Volumetric water content sensors were embedded in each trench, and the data were used for water flow calibration and validation. The performance of the calibrated and validated model was evaluated by model efficiency (NSE), index of agreement (IA), and root-mean-squared error (RMSE). Values for calibration included a NSE of 0.65, IA of 0.87, and RMSE of 0.005. For validation, the NSE was 0.68, IA was 0.86, and RMSE was 0.004. All of the values met the quality of modeling criteria, $NSE > 0.5$ , $IA > 0.8$ , and $RMSE < 0.014$ . Chemical wastewater parameters such as chemical oxygen demand (COD), total nitrogen (TN), ammonium, and nitrate were measured during experimentation and used to calibrate and validate the solute flow components of the model using a trial-and-error method. Except for ammonia, the largest relative difference in COD and nitrate between the measured and simulated values were 10.6% and 10.4%, respectively. Although ammonia had a large relative difference, with values between 0.1 and $0.26 mg / L$ N, this is not significant with respect to field conditions. The results from the calibrated HYDRUS CW2D model can help evaluate the performance of land-based wastewater treatment systems and reduce negative impacts of this type of treatment system.