Evaluation of the Efficiency of Constructed Wetlands in Pollutant Removal from an Urban Stream in the Semi-Arid Region of Ceará

Abstract

This study evaluated the efficiency of constructed wetlands implemented in the municipality of Sobral, based on 15 monitoring campaigns conducted by the municipal government. The analyzed variables included pH, turbidity, dissolved oxygen, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen, total phosphorus, and total coliforms. The results indicated that both influent and effluent waters had pH values near neutrality. However, the high concentrations of BOD, COD, nutrients, turbidity, and coliforms suggest the presence of illegal sewage connections. Although the systems showed good removal rates in some campaigns, these were not consistent, indicating potential operational failures. The variability in removal efficiencies and the low levels of dissolved oxygen in some samples (below 2 mg/L) point to organic overload and the need for operational improvements. The highest removal efficiencies were observed during the dry season. The study reinforces the importance of constructed wetlands as nature-based solutions, which complement conventional sanitation and stormwater drainage infrastructure. When properly managed, such systems can significantly contribute to improving the water quality of urban rivers, serving as a valuable tool to support public policies aimed at controlling diffuse pollution and promoting urban environmental planning.