Constructed wetlands are engineered systems designed to mimic the natural processes of wetlands. They use vegetation, soil, and microorganisms to treat wastewater by filtering out pollutants and improving water quality. These systems can be used for various applications, including treating municipal sewage, agricultural runoff, and industrial effluents. The design of constructed wetlands can vary, but they typically consist of shallow basins filled with gravel or soil, planted with native wetland plants. As water flows through these systems, the plants and microorganisms break down contaminants, making the water cleaner before it is released back into the environment.