Design of a Constructed Wetland as a Nature-Based Solution for the Japanese Garden Lagoon, La Paz, Bolivia

The Japanese Garden of La Paz, Bolivia, is a sociocultural space with high biodiversity, with its lagoon receiving treated effluent from the “Las Cholas” Wastewater Treatment Unit. Preliminary monitoring revealed elevated organic matter concentrations, raising concerns about water quality. This study aimed to design a constructed wetland (CW) to remove organic load and demonstrate its potential as a nature-based solution (NBS) for sustainable management. Physicochemical parameters and the trophic state index were evaluated during the dry and wet seasons. Macrophyte species were identified, and the most suitable species were selected through a systematic literature review considering treatment performance and local availability. The results showed alkaline conditions, low nutrient concentrations, and a mesotrophic trophic status. A total of 139 vascular plant species were recorded, including Cyperus involucratus, Azolla filiculoides, and Eichhornia sp. Cyperus involucratus was selected due to its abundance and reported BOD5 or COD removal efficiency. The proposed system consists of a horizontal subsurface flow CW incorporating permeable reactive barriers filled with water hyacinth leaves as a biosorbent. A design flow rate of 0.86 m3/day was adopted for the proposed CW, corresponding to a hydraulic retention time (HRT) of 1.68 days and an estimated BOD5 removal efficiency of 68.54%.