Constructed Wetlands Wastewater Treatment

     In response to Columbia’s need to increase its wastewater treatment capacity and to protect the water quality of Perche Creek, the City of Columbia has upgraded the existing treatment plant and constructed a wetlands wastewater treatment addition.  Constructed wetlands clean wastewater in the same way that natural wetlands cleanse surface water of nutrients and organic debris.  Both systems rely on natural biological processes.

    Wetland Units 1 & 2
    Wetland Units 1 & 2
    Wetland Units 3 and 4
    Wetland Units 3 and 4

    Background

    By 1987 Columbia’s population had nearly outgrown the existing wastewater treatment facility.  At that time the City proposed a conventional plan of expanding the existing treatment facility and constructing an effluent pipeline to the Missouri River.  However, this plan did not satisfy the citizens of the community.  Columbians cried out for a more natural approach.  After additional engineering studies, Columbia adopted the idea of using constructed wetlands for further wastewater treatment.

    Roots and stems of wetland vegetation provide a home for naturally occurring micro-organisms.  Wastewater nutrients fertilize the wetland vegetation and organics provide a food source for the micro-organisms.  Through this process, water leaving a wetland has been “treated” naturally. 
     
    Unlike naturally occurring wetlands, constructed wetlands for wastewater treatment are constructed to control flow of water through the vegetation.  Constructed wetlands are designed for a known amount of wastewater flow, and the size of the wetlands is based on the level of treatment needed to return the water to the environment without harmful effects. 
     
    Wastewater processed at the Columbia Regional Wastewater Treatment Plant flows to the constructed wetlands for final treatment.  The wetlands and wastewater treatment plant upgrades have increased Columbia’s treatment capacity from 13 million gallons per day (MGD) to approximately 20 million gallons per day.
    Wetlands

    Wetland plants have the unique ability to transport oxygen to support their roots growing in anaerobic substrates. 
    Illustration reprinted by permission from Constructed Wetlands for Wastewater Treatment, 1989 Lewis Publishers, Inc.

    Construction

    Overwhelming approval (95%) of a bond issue in 1990 allowed the City to begin wetlands construction in 1991.  These constructed wetlands are made up of separate treatment “units” located along the MKT Trail near Perche Creek and the town of McBaine.  Three wetland treatment units were completed in 1994 and a fourth was completed in 2001.  The wetland treatment units are divided into “cells” so maintenance can be done without disturbing treatment in a whole wetland unit.  The total treatment water surface area of Columbia’s constructed wetlands is approximately 130 acres.

    Typical Treatment
    Each constructed wetland unit is lined with a minimum of 12 inches of compacted clay to keep the wastewater from leaching out.  The clay liner is covered with 6 to 12 inches of topsoil and cattails are planted throughout the units.

    Cattails are favored for Columbia’s constructed wetlands for many reasons, including their ability to survive in this climate, and to grow fast and dense.

    Flood control berms surround each constructed wetlands treatment unit for protection from the Missouri River.  The berms are planted with grasses.

    Wetland CellsBenefits

    The constructed wetlands and wastewater treatment plant upgrade will provide the Columbia area with adequate wastewater treatment capacity for population and business growth for years to come.

    Treated effluent from the constructed wetlands benefits the Missouri Department of Conservation (MDC) by providing a consistent water source for the Eagle Bluffs Conservation Area.  In a unique cooperative agreement between the City of Columbia and MDC, Eagle Bluff’s design was modified to use effluent from Columbia’s constructed wetlands as its primary source of water.  This conservation area is located south of Columbia’s constructed wetlands, bordered on the west by the Missouri River and on the east by Perche Creek.  MDC acquired the conservation area in 1989 as part of a statewide wetland restoration and management program.  Completed in 1995, Eagle Bluffs includes about 4,400 acres of wetland in emergent marsh and seasonally flooded, moist-soil ponds.

    Eagle Bluffs is a valuable educational and recreational resource.  For more information on Eagle Bluffs Conservation Area, call the MDC field office at 573-445-3882.

    Wildlife also benefits.  The constructed and restored wetlands provide habitat for many resident and migrating marsh and waterfowl.  Bald eagles are routinely sighted in the Eagle Bluffs area.  Bird watchers appreciate the proximity of the MKT and Katy (hiking/biking) Trails.

    Summary

    Wetland Pump Station

    Columbia’s Constructed Wetlands Wastewater Treatment Project has captured the imagination and support of citizens, environmentalists and regulatory agencies.  It has drawn nationwide interest as an example of community initiative and creativity.

    This complete cycle of taking water from the ground, using it for the needs of the people of Columbia, cleansing it through natural processes, and using it to restore valuable wetland habitat show Columbia’s commitment to high environmental standards.

    The Daniel Boone Regional Library is an excellent source for general information on wetlands.