Horizontal Subsurface Constructed Wetlands for Landfill Leachate Treatment: Substrate Selection and Macrophyte Adaptation Study

Abstract

Municipal solid waste management remains a critical global issue, with landfill leachate as a significant environmental challenge due to its complex and often toxic nature. Traditional treatment methods are not only expensive but often struggle to adequately manage these contaminants. Constructed wetlands (CWs) offer a promising and sustainable alternative, capable of providing effective treatment at a lower cost. This study examines the performance of 12 microcosms designed to simulate horizontal subsurface flow constructed wetlands (HSCWs) for the treatment of landfill leachate. The microcosms, in a greenhouse, utilized a combination of river gravel (RG) and autoclaved aerated concrete (AAC) as substrates. Six microcosms were planted with Typha domingensis, and six were unplanted, serving as controls. Contaminants such as pH, alkalinity, electrical conductivity, total phosphorus (TP), total suspended solids (TSS), ammonium (NH4+), nitrite (NO2−), nitrate (NO3−), total Kjeldahl nitrogen (TKN), biological oxygen demand (BOD5) and chemical oxygen demand (COD) were measured weekly over a two-month period at inlet and outlet samples. A gradual dilution approach was employed to acclimate the macrophytes, which significantly enhanced their survival and treatment performance. The results revealed that microcosms using AAC substrates exhibited improved removal efficiencies for several compounds underscoring the benefits of AAC in constructed wetland systems. These findings suggest that HSCWs, particularly those incorporating AAC, provide a viable and effective solution for landfill leachate management. ACC treatments, T2 and T4, obtained removal efficiencies: 91% and 89% for SST; 69% and 73% for TKN; 78% and 80% for NH4+; −1,383% and −1,540% for NO3−; −156,309% and −251,592% for NO2−; 96% and 99% for NO2−; 77% and 82% for BOD; 43% and 52% for COD, respectively. This research highlights the potential of CWs to serve as an environment friendly alternative to traditional treatment methods and sets the stage for future studies focused on optimizing CW designs and substrate choices to further improve pollutant removal and advance sustainable waste management practices.