Influence of operational conditions on the efficiency of Wolffia brasiliensis for polishing domestic wastewater of facultative stabilization ponds

Stabilization ponds are widely used for wastewater treatment in developing countries but have limitations in removing certain pollutants, necessitating polishing processes to enhance effluent quality and mitigate environmental impacts. Aquatic macrophytes, particularly Lemnaceae , offer a low-cost, efficient alternative due to their rapid reproduction and high nutrient absorption. This study evaluated the effects of operational conditions on Wolffia brasiliensis development and its efficiency in polishing wastewater from facultative stabilization ponds. The parameters assessed were chemical oxygen demand (COD), biochemical oxygen demand (BOD₅,₂₀), total nitrogen (TN), and total phosphorus (TP). Three cultivation conditions were tested: untreated effluent, recirculated effluent (6 × 10⁻³ L s⁻¹ flow rate), and 10% diluted effluent. Experiments were conducted indoors (21,818 lux, 24°C ± 1.3°C) and outdoors (natural conditions, 31°C ± 3.5°C). Biofilm formation hindered macrophyte growth and contaminant removal in outdoor units. Indoor conditions yielded higher biomass (85.87 ± 11.9 g m⁻² d⁻¹) than outdoor ones (31.35 ± 9.3 g m⁻² d⁻¹). Recirculated effluent led to the highest growth rates (42.06 ± 33.1 g m⁻² d⁻¹ indoor, 15.70 ± 11.7 g m⁻² d⁻¹ outdoor). All W. brasiliensis units significantly improved pollutant removal compared to controls. These findings highlight W. brasiliensis as an effective, sustainable solution for polishing effluents from facultative stabilization ponds, particularly for BOD₅,₂₀, COD, TN, and TP removal, reinforcing its potential for wastewater management in developing countries.