Wetland Assimilation

The use of wetlands is a long-term solution for your water quality needs.

      A properly designed system can function for long periods of time because natural processes in the wetlands achieve water quality improvement. Using a wetland approach to solve wastewater problems would reduce cost and result in clean water. For example, the City of Breaux Bridge has discharged treated effluent into a forested wetland for over 60 years and the system is healthy and continues to result in greatly improved water quality. The basic principle underlying wetland wastewater assimilation is that the rate of application must balance the rate of decay or immobilization. The primary mechanisms by which this balance is achieved are physical settling and filtration, chemical precipitation and adsorption, and biological metabolic processes resulting in eventual burial, storage in vegetation, and denitrification.

Well-designed wetland assimilation systems have the following benefits:

• Wetland assimilation can achieve tertiary levels of treatment. Nutrient levels are reduced to background and thus it is not necessary to set nutrient limits on effluents. Tertiary treatment using conventional methods is very expensive.
• Wetlands result in less stringent effluent limits because of the assimilative capacity of wetlands. For example, limits for BOD are often 30 to 45 mg/l and limits for TSS are often 45 to 90.
• Because of the assimilative capacity of wetlands, these systems do not contribute to TMDL load calculations.
• Effluent discharge results in enhanced wetlands with higher productivity.
• Effluent discharge to wetlands results in increased accretion and thus the ability to survive rising water levels. Because of the increased productivity and accretion, discharge of treated effluent can be viewed as a coastal restoration tool and as a form of mitigation.
• Wetland assimilation systems are much more cost-effective and energy efficient that conventional treatment systems. This is true for both construction and operation costs. This is especially important in a time when energy is becoming much more expensive.
• Discharge of treated effluent to subsiding coastal wetlands results in significant carbon burial or sequestration thus contributing to a reduction of carbon dioxide increase in the atmosphere.
• Wetland assimilation offers long-term employment opportunities in the operation of these systems. Wetland assimilation offers the possibility of a long-term revenue stream based on household user fees.

Ecological Perspective