Effect of temperature and loading frequency on the performance of vertical subsurface flow constructed wetlands: Modelling study using HYDRUS

Constructed wetlands are used in wastewater treatment for the removal of organic matter, nutrients, pathogens and other pollutants from water. The diversity of chemical, physical and biological processes taking place inside constructed wetlands (CWs) make them difficult systems for accurate quantitative description through conventional modelling approaches. However, existing modelling tools can bring valuable insight into important phenomena and interactions that might remain otherwise neglected. In this study the CW2D module under HYDRUS – 2D is used to identify the possible mechanisms by which temperature and loading frequency impacts the performance of the vertical subsurface flow constructed wetlands (VSSFCWs). An improvement on CWs design and operation guidelines in warm regions is intended. Case studies of a VSSFCW at 10°C, 20°C and 30°C treating septic tank effluent are simulated with parameters adjusted for high temperature conditions. The simulation results suggest oxygen limitation as possibly constraining nitrification capacity at high temperatures. Simulations also suggest that higher loading frequencies enhance performance and capacity. This detailed mechanistic modelling study aims at bringing insight into possible non trivial interactions and mechanisms in CWs such that in conjunction with a necessary experimental validation, should lead to enhanced operation and design in warm regions.