Constructed Wetland with Subsurface Flow for Treatment of Olive Mill Wastewater in Mediterranean Regions

Abstract

Olive mill wastewater generated in Mediterranean regions contains high concentrations of organic matter, suspended solids, phenolic compounds, and dissolved salts, posing significant environmental challenges when discharged without proper treatment. The present study investigates the application of a subsurface flow constructed wetland system for the treatment of olive mill wastewater under controlled environmental and operational conditions. The research focuses on evaluating organic pollutant removal, nutrient reduction, hydraulic performance, and treatment efficiency associated with subsurface wetland processes. Experimental analysis was conducted to assess the influence of hydraulic retention time, substrate composition, vegetation type, wastewater loading rate, and seasonal climatic conditions on contaminant removal and overall system stability. Results demonstrate that subsurface flow constructed wetlands effectively reduce chemical oxygen demand, biochemical oxygen demand, suspended solids, and phenolic compounds through integrated physical, chemical, and biological treatment mechanisms. The study further reveals that microbial degradation, sediment filtration, plant uptake, and adsorption within the wetland substrate contribute significantly to pollutant removal and wastewater stabilization. Optimized retention time and vegetation establishment were found to enhance treatment efficiency while minimizing odor generation and surface contamination risks. Comparative assessment with conventional physicochemical treatment methods confirms that constructed wetlands provide advantages including lower energy consumption, reduced operational costs, and improved environmental sustainability.