Horizontal Subsurface-Flow-Constructed Wetlands with Tropical Vegetation for the Treatment of Landfill Leachate: Case Study in Cartagena, Colombia

Abstract

Landfill leachate in developing countries is often discharged into the environment without treatment because most treatment technologies have high costs and are highly complex, making their implementation infeasible. This research evaluates the technical feasibility of implementing constructed wetlands with horizontal subsurface flow for the treatment of raw leachate and leachate pretreated with photo-Fenton of the Loma de los Cocos landfill in the city of Cartagena, Colombia. In order to evaluate the vegetation performance, three wetland modules were constructed: one without vegetation (HC), one with Rhizophora mangle (HM), and one with Typha latifolia (HE). Two tests were performed: one with raw leachate and another using pretreated leachate with photo-Fenton, which is considered a suitable treatment for little or moderately biodegradable waters. The modules were operated with a hydraulic retention time of 8 days and an operating time of 16 days. For the photo-Fenton pretreatment, the pH of the leachate was adjusted to values between 2 and 3 using a molar ratio Fe2+/H2O2 of 0.6 at a retention time of 40 minutes. The raw leachate was characterized as having chemical oxygen demand (COD) concentrations between 3,000 and 4,800 mg L−1 and pH values above 7.5. In general, wetlands had higher efficiencies with pretreated leachate. The effluent COD concentrations obtained in all tests complied with the maximum limit established by current Colombian regulations (2,000 mg L−1). During the pretreated leachate test, the HE constructed wetland had pollutant removals that were slightly higher than the mangrove sown wetland (HM): COD (HE: 77%; HM: 73%), chloride (HE: 58%; HM: 50%), sulfate (HE: 58.6%; HM: 54.5%), nitrite (HE: 54.7%; HM: 67%), nitrate (HE: 98.4%; HM: 90.5%), and TDS (HE: 56%; HM: 54%). Although the HM wetland had removal average efficiencies that were slightly lower than those of the HE wetland, it can be concluded that horizontal subsurface-flow constructed wetlands with both vegetation are a viable alternative for the treatment of leachate from the Loma de los Cocos landfill.