Pilot Constructed Wetlands Project
In 1990 staff began to research the use of constructed wetlands to treat landfill leachate as a viable option versus conventional treatment. At this time the use of constructed wetlands as treatment systems was relatively new and there were no existing projects that used them to treat landfill leachate specifically. In 1992 staff chose to pursue wetland treatment options further based on preliminary findings and began moving forward with the design of a pilot system. The primary purpose of the pilot constructed wetlands project was to determine the feasibility and treatment efficiency achieved by using manmade wetlands to treat landfill leachate.
In July 1993, New Hanover County’s Department of Environmental Management was awarded a Coastal Area Management Act (CAMA) grant from the North Carolina Division of Coastal Management. The grant was awarded to fund the development of an educational program to be used in conjunction with the constructed wetlands pilot project. The educational program targets junior high school students and teaches them the importance of and the effects of specific pollutants on water quality. Parameters tested for include ammonia nitrogen, pH, dissolved oxygen, nitrates/nitrites, and total nitrogen.
In October of 1994 a second grant was awarded by the Water Environment Research Foundation to North Carolina State University to conduct research on the project. The North Carolina Sea Grant program was also involved in the construction of the system and research conducted at the site.
The pilot project consists of two surface flow wetland cells and three subsurface flow wetland cells. In the surface flow cells there is approximately twelve inches of surface water in which leachate is allowed to flow through freely prior to exiting the system. In the subsurface flow cells leachate is forced to flow through rounded river rock below the surface before exiting the system. Wetland plants were established in the Spring of 1995 and leachate was gradually introduced beginning in September of the same year. The wetland system was then monitored over the following four year period.
Species of plants in the pilot system include:
Softstem bulrush/Scirpus validus
Pickerel weed/Pontederia cordata
Soft rush/Juncus effusus
Arrow arum/Peltandra virginica
Lizard's tail/Sarurus cernuus
The system proved to be a viable treatment option. Results of the research indicated that the constructed wetlands could be used for either primary or tertiary treatment. Other benefits from using constructed wetlands versus conventional treatment include providing wildlife habitat, creating an aesthetically pleasing treatment system, create educational opportunities, research opportunities, lower operation and maintenance costs, and lower capital costs. Students and interns from both the University of North Carolina in Wilmington and North Carolina State University have participated in various stages of the project or have used the wetlands to conduct research for Masters and Ph.D. degree thesis. The research results obtained led New Hanover County to pursue construction of a full scale system. In 2002 New Hanover County was awarded grant funding in the amount of $785,000 from the Clean Water Management Trust Fund. This money was used in conjunction with $243,500 of matching funds from New Hanover County to design and construct the system.
Full Scale Constructed Wetlands
The full scale constructed wetland treatment system is capable of treating all the leachate generated at the landfill. The landfill now operates this 5.66 acre wetlands treatment and irrigation system designed to treat up to 60,000 gallons/day. The treated leachate from the wetlands is irrigated onto closed landfill space as low grade liquid fertilizer. Currently the system treats approximately 7,000,000 gallons of leachate each year. This total represents approximately 40% of our permitted discharge to the Northeast Cape Fear river from the wastewater treatment plant.
As additional landfill space is closed in the future, the irrigation system will be extended in order to irrigate more treated leachate. Eventually, the use of constructed wetlands and irrigation will allow us to eliminate the wastewater treatment plant and our discharge to the river. In essence, closing the loop by re-directing and reusing our treated leachate in an effort to protect the water quality of surface waters in southeast North Carolina from pollutants leaving our facility. This system serves as a model for other industries and municipalities as an alternative to conventional treatment practices. The wetland treatment system is cost effective, aesthetically pleasing and provides wildlife habitat. The irrigation of treated leachate also cuts costs by helping to maintain and increase the vegetative cover of our closed landfill space as well as to protect the landfill side slopes from storm water erosion.
Both constructed wetland projects have gained international attention. Representatives from the government of Thailand and India have visited and shown interest in the project as potential low cost alternatives versus conventional treatment as their countries continue to develop.
For additional information or to arrange facility tours, presentations, or participate in the Constructed Wetlands project, call 798-4400.