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/m 2 .d) in green roof systems. Both plant species demonstrated good adaptability and growth under effluent exposure. At a high hydraulic loading rate (50 L/m 2 .d), green roofs planted with Campsis radicans achieved removal rates of 13.96 ± 2.14 gCOD/m 2 .d for organic matter, 0.96 ± 0.24 gN/m 2 .d for total nitrogen, and 0.02 ± 0.01 gP/m 2 .d for total phosphorus. These values were nearly four times higher than those at the lower hydraulic loading rate (16 L/m 2 .d). Vernonia elliptica showed slightly better pollutant removal efficiency compared to Campsis radicans and also provided a larger green coverage area (6 m 2 ), 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.