What are “Polishing Wetlands”?
Polishing wetlands are designed and built by process-engineers to filter wastewater, after it has already passed through primary and secondary purification processes, to lower suspended solids and organics. Polishing wetlands are usually designed to be the terminal component of a wastewater plant and contain wetlands plants, such as tules, over one-quarter-to-one-half of the wetlands’ surface area. These plants further remove organics, metals, fertilizer chemicals, and other pollutants from the water, making the output water up to 70% purer than the secondary treated. In modern wastewater treatment plants, there are usually three-to-five such polishing wetlands linked together in a serial manner, each wetland 10–30 acres in size, depending on the size of the main treatment plant.
The ponds are designed to be two-to-five-feet deep and usually move the water slowly from pond-to-pond by gravity. Water exiting these ponds can be used on parks, golf courses, and farm fields, greatly reducing the need to use potable water for these tasks. These ponds and their accompanying vegetation form perfect habitats for marsh animals and frequently cannot be distinguished from natural marshes within two-to-three years of establishment. They usually become meccas for birders and naturalists.