CEA Constructed Wetlands at Akumal Retrofitted to State of the Art

The Planetary Coral Reef Foundation in partnership with CEA built the first constructed wetlands at Akumal in 1994. They were built under the direction of Dr. Mark Nelson, then a graduate student at the University of Florida, as part of his doctoral dissertation. CEA contributed $9000 to the project. Since the first wetlands were built, wetland engineers have published many technological improvements in wetland design. Further, Akumal has grown, including the areas served by the wetlands. Since the wetlands were first constructed we have seen the opening of the Turtle Bay Bakery, La Cueva del Pescador, the Internet Café, three gift shops and Peak Gym. In addition, the number of people using the CEA dormitories has increased. This growth has placed demands on the wetlands that exceed their original design limits. For these reasons, it was decided to bring our demonstrations wetlands back to the state-of-the-art from which they started.

In June 2003, CEA received a grant from the National Fish and Wildlife Foundation to pay for the retrofit, which is under the supervision of CEA wetland engineer Kate Riley. Kate is working with CEA laboratory technician David Nuñez, who is tracking the chemical and bacteriological processes taking place within the wetlands.

Work on the retrofit began October 1 and is now nearly completed. First, the plants were removed and stored for later use. Local contractor Jaime Medina removed the old gravel using a back loader and cleaned out the concrete structures that contain the wetlands. It had been anticipated that the gravel removal might be a very odiferous operation, so CEA advised the local businesses and timed the removal of gravel to coincide with low season, when some businesses close. To the surprise of everyone, there were no bad odors, just of soap. It appears that the organic treatment was sufficient to remove odor-causing bacteria and that the major residue was from soaps and shampoos. The concentration of soaps accounts for the very high pH values (9.2) measured in the wetlands last summer. There was no evidence of dissolution of the limestone gravel, which had been suggested as the reason for a pronounced compaction of the gravel in the wetland.

Once the gravel was removed and the structures cleaned, the concrete walls and floor were examined and found to be sound and without cracks. Next, Kate Riley and Jaime redesigned the plumbing so that the flow of fluid passed along the length of the wetland, rather than across the narrow dimension. This has the effect of extending the residence time in the treatment cell. Residence time is an essential feature of wetland design, because the bacteria that destroy pathogens and the absorption of nutrients by the plants both require about a week to effectively cleanse raw sewage.

A major feature of the retrofit was the addition of an aeration system. This system, which consists of a hose with pinholes laid along the bottom of the concrete cell through which air is forced by a pump, is reported to increase the effectiveness of treatment five-fold. Through regular sampling and testing, David Nuñez will be tracking the efficiency of the improved system.

Finally, new gravel was put into the cells and, as I write, Kate Riley is replanting with carefully-selected plants that use lots of water and thrive in tropical settings.

The grant from the National Fish and Wildlife Foundation continues through June of 2004 and will pay for testing in the retrofitted CEA wetlands and for regular sampling of private wetlands and natural lagoons and mangroves in the Akumal area.

Reported by Charles Shaw

For more information on this project click here.
To learn more about constructed wetlands click here.
To learn more about our Advanced Waste Treatment program click here.