Constructed wetlands implemented for the Triangle School Wastewater Treatment System consist of a series of plots filled with crushed brick, sand, and gravel. The plots are lined with plastic to prevent waste from leaching into groundwater, and are populated by native wetland plants to aid in wastewater treatment. These constructed wetlands mimic nature by mechanically filtering, chemically transforming, and biologically consuming potential pollutants in the wastewater stream. (More on constructed wetlands.)
Two types of constructed wetlands are shown below. Both cell 1 and cell 2 of the Triangle School Wastewater Treatment Facility are deigned using variations of the low marsh and high marsh constructed wetlands.
The plants grown in these plots are specifically chosen for their ability to assist in the biological treatment of water. Plants act like biological pumps, converting sunlight into chemical energy and carrying oxygen from their leaves to their roots. Pollution eating microbes colonize in the oxidized zone surrounding the root surface. Microbes convert nitrates into a harmless gas.
Alternating aerobic and anaerobic environments work together to remove nitrogen from wastewater. Phosphorus is reduced as it chemically binds to crushed brick, and biological oxygen demand (BOD) created by organic materials and other substances is filtered out or eaten by microbes. BOD and phosphorus removal are relatively quick processes requiring an aerobic environment, while nitrogen transformation takes several days.