Phytoremediation of septic tank effluent using green roof systems planted with Vernonia elliptica and Campsis radicans

Rapid urbanization has led to a reduction in green spaces and an increase in the discharge of untreated wastewater, posing significant environmental challenges. Green roof systems offer a sustainable solution by integrating vegetation into urban infrastructure to deliver ecological and wastewater treatment benefits. This study evaluated the performance of two ornamental climbers, Vernonia elliptica and Campsis radicans, in treating septic tank effluent under two hydraulic loading rates (16 and 50 L/m2.d) in green roof systems. Both plant species demonstrated good adaptability and growth under effluent exposure. At a high hydraulic loading rate (50 L/m2.d), green roofs planted with Campsis radicans achieved removal rates of 13.96 ± 2.14 gCOD/m2.d for organic matter, 0.96 ± 0.24 gN/m2.d for total nitrogen, and 0.02 ± 0.01 gP/m2.d for total phosphorus. These values were nearly four times higher than those at the lower hydraulic loading rate (16 L/m2.d). Vernonia elliptica showed slightly better pollutant removal efficiency compared to Campsis radicans and also provided a larger green coverage area (6 m2), enhancing the aesthetic and ecological value of the green roof. These findings highlight the dual functionality of green roofs as a decentralized wastewater treatment system and a contributor to urban greening.