Biogardens as constructed wetlands in tropical climate: A case study in the Central Pacific Coast of Costa Rica

In Costa Rica, <10% of wastewater is treated before its discharge. This generates a significant impact on the environment, public health, and tourism industry, which is one of the country's main economic activities. Biogardens, subsurface flow artificial wetlands, are alternative systems for the treatment of wastewater. The present study evaluated the removal of organic matter and nutrients in a biogarden located at a hotel in the Central Pacific Coast of Costa Rica between 2012 and 2017. Pretreatment involved septic tanks and grease traps for sewage and gray water, respectively. The biogarden, which is composed of seven wetlands with an average area of 12 m² and a depth of 0.7 m, contains river cobble as support material, gravel as bed, and Cyperus papyrus and Heliconia sp. plants. Removal of the biochemical oxygen demand (BOD), the chemical oxygen demand (COD), and the total suspended solids (TSS) on average were 80%, 66%, and 72%, respectively, thus producing an effluent in compliance with current national legislation. Furthermore, the biogarden did not emit noxious odors or display an excessive presence of mosquitoes. The results showed consistent and efficient removal of organic matter and nutrients from the wastewater throughout different seasons and pollutant loads, verifying that such systems can be used in decentralized locations (e.g., tourist areas) in tropical climates.