Attenuation of Aqueous Naphthalene through a Constructed Wetland System Employing Lightweight Expanded Clay Aggregate

Naphthalene (NAPH), a common polyaromatic hydrocarbon from the petrochemical and pharmaceutical industries, significantly contaminates water bodies due to its resistance to degradation. This study investigated the use of the lightweight expanded clay aggregate (LECA) in attenuating aqueous NAPH in wastewater. The methodology involved batch adsorption, vertical column experiments, and laboratory-scale constructed wetland tests validated by the HYDRUS 2.05 (2D/3D) numerical model. Batch adsorption tests achieved a maximum efficiency of 96.48% at 12 mg/L NAPH concentration. In this regard, two models were tested: Langmuir and Freundlich models. The Freundlich model [coefficient of regression R2 = 0.99, isotherm coefficient Kf = 0.07914 (mg/g) (L/mg)] and the pseudo-second-order kinetic model [K2 = 0.395 (g/mg min), R2 = 0.98] best described the observed data. Sorption decreased with increasing pH (84% at pH 2 to 47% at pH 10) and was minimally affected by temperature. Vertical column tests showed bed exhaustion at 36 h, while the constructed wetland system incorporating LECA reduced NAPH concentration by up to 97.5%, corroborated by HYDRUS model results. Recyclability tests demonstrated 100% removal efficiency for up to 120 cycles, declining to 0 by the 270th cycle. These results indicated that LECA-based constructed wetlands are an efficient and sustainable method for mitigating NAPH contamination, supporting Sustainable Development Goal 6 for clean water and sanitation.