Seasonal evaluation of pollutant removal in a vertical constructed wetland in Tunisia’s arid climate

Intermittent planted filters are effective biological treatment systems designed to oxidize and purify urban wastewater at a low cost while minimizing environmental impacts. This study introduces a novel adaptation of vertical flow constructed wetlands (VFCWs) specifically tailored to the arid climate of southeastern Tunisia, with a focus on optimizing seasonal performance and addressing regional wastewater treatment challenges. By integrating a unique two-stage gravel-sand design, both stages of which are fed vertically, and leveraging solar-powered operations, this research offers valuable insights into the dynamics of pollutant and pathogen removal under extreme environmental conditions. Through a combination of laboratory and field experiments, the research demonstrated significant reductions in chemical oxygen demand, biochemical oxygen demand, ammonia-nitrogen, and ortho-phosphate, achieving removal efficiencies of 95.2%, 96.1%, 78.2%, and 100%, respectively. Notably, an increase in nitrate levels at the filter outlet suggests favorable nitrifying conditions that may enhance plant physiological growth. The treatment system also effectively removed 2, 1.56, and 1.18 log units of total coliforms, fecal coliforms, and fecal streptococci, respectively. Seasonal variations, particularly in air temperature and sunlight duration, significantly influenced pollutant removal rates, with higher efficiencies observed during the warmer summer and spring months, which promote both plant growth and microbial activity.