Wetland systems for bioregenerative reclamation of wastewater: from closed systems to developing countries

Results are presented from constructed wetland systems designed to treat wastewater in Akumal, Quintana Roo, Mexico, which was developed after prior experience with the Biosphere 2 closed ecological system wetland systems. These systems illustrate the congruity of needs in advanced life support systems and in solving social and environmental problems in developing countries. For sustainable food production for life support, closed ecological systems need to bioregenerate and recycle nutrient-rich wastewater. Developing countries need low-tech ecologically engineered systems that minimize requirements for capital, nonrenewable energy, and technical expertise. Biosphere 2's surface flow wetlands covered 41 m2 and treated the wastewater from eight inhabitants, laboratories, and domestic animals during the 1991-1993 closure experiment. The Mexican wetlands are subsurface flow wetlands using limestone gravel as substrate. Two wetland systems treat sewage from 40 people and cover 131 m2. During the initial year of operation, the wetlands in Akumal reduced BOD 86%, TSS 39%, total P 80%, total N 75%, and coliform bacteria 99.85%. Phosphorus uptake in the limestone gravel was around 6 mg/kg. High biodiversity, with 70 plant species, was maintained in the Akumal constructed wetlands 1.5 years after planting. The Shannon diversity index was 4.7 (base 2). Plant diversity was slightly less than tropical forest ecosystems of the region, but far greater than biodiversity in natural mangrove wetlands.