Flow Dynamics around a Floating Vegetation Island and Sediment Removal: Field and Lab Studies with Engineering Education Applications

Abstract

This work addresses the need for innovative solutions to improve water quality in urban areas where sanitation infrastructure is often inadequate. Intensive urbanization has led to a significant increase in surface runoff and pollutant load, resulting in substantial challenges for public health and the environment. Floating Treatment Islands (FTIs) emerge as a promising technology, using floating vegetation to remove pollutants through physical and biochemical processes, contributing to environmental sustainability and improving the quality of life in cities. This thesis aims to evaluate the hydrodynamic behavior of a low-cost floating vegetation island (FVI) prototype in an urban stream, develop a reduced-scale floating vegetation island structure to conduct controlled hydrodynamic experiments in the laboratory, and conclude with the development of Project-Based Learning (PBL), encouraging students to expand their knowledge and prepare for the future. The first chapter used roots of Pistia stratiotes in the implementation of a low-cost floating vegetation island in an urban stream. Suspended solids adsorption was quantified, and the relationship with the characteristics of the root zone was analyzed. Results showed that the water velocity through the root zone reduced by an average of 60%, and sediment capture was related to root mass with a determination coefficient (r²) of 0.5. However, there was no progressive reduction in the amount of captured mass, possibly due to the non-uniformity of root biomass and fluid behavior. The second chapter investigated the hydrodynamic effects of FVIs composed of Pistia stratiotes roots in an experimental channel. The objective was to analyze how different root configurations influence hydrodynamic behavior and sediment removal efficiency. Experiments were conducted at the Laboratory of Energy Efficiency and Hydraulic Sanitation (LENHS) using a 20-meter channel with Acoustic Doppler Velocimeter (ADV) velocity measurements. Three root lengths (h0/H = 0.3, 0.6, and 0.8) were tested. Results indicated that longer and deformed roots increased mass removal efficiency, but the sediment removal rate decreased over time, suggesting a system saturation time. The distribution of turbulent kinetic energy (TKE) and Reynolds stresses was significantly affected by the presence of the roots, with greater energy redistribution near smaller, less flexible roots. The flow velocity recovery varied with root length, highlighting the complex interaction between fluid flow and root reconfiguration. The third chapter explored the impact of Project-Based Learning (PBL) in engineering education, specifically in a Transport Phenomena course at UFMS. The objective was to evaluate how integrating FVIs into practical projects influences student engagement and learning outcomes. PBL allowed students to apply creative and analytical skills in a practical context, optimizing water flow through the root zone. Results showed significant variation in project grades, with a higher standard deviation among students with averages above the passing threshold, indicating diverse approaches, and a lower standard deviation among those near the passing threshold, suggesting uniform efforts. Students reported high satisfaction with PBL despite challenges in data interpretation, highlighting the need for adaptive teaching methods to improve engagement and learning.