The influence of pollutants on plant growth and treatment efficiency of horizontally-constructed wetlands

Abstract

Constructed wetlands (CWs) have been widely used for wastewater treatment due to advantages such as low cost and easy operation. However, pollutant concentrations directly affect treatment efficiency by inhibiting plant and microbial growth. This study aims to evaluate the relationship between pollutant concentrations, tolerance of plants, and treatment efficiency of horizontal subsurface flow (HSF) CWs receiving synthetic wastewater. The results showed that Cyperus alternifolius L. grew well in conditions with concentrations of chemical oxygen demand (COD) and NH₄⁺ up to 75 and 125 mg/l, respectively, and pH 5-8. The lowest treatment efficiency was 56.7% at an initial COD concentration of 1000 mg/l. There were several dead plants in the CWs with a NH₄⁺ concentration of 200 mg/l. When the initial COD and NH₄⁺ concentrations were in the range of 500-750 and 75-125 mg/l, respectively, the treatment efficiencies of organic matter (COD) and NH₄⁺ were 82.5-85.1 and 31-69.7%, respectively. The pH value was stable at a neutral level during the treatment process. The concentration ranges of COD (500-750 mg/l) and NH₄⁺ (75-125 mg/l) were the optimal thresholds for pollution control while also ensuring normal plant growth. This study serves as a basis for considering wastewater characteristics in the design of HSF CW systems in practice.