RÉSUMÉ
Constructed wetlands (CWs), crucial for the rural decentralized wastewater treatment, have encountered limitations in nutrient removal efficiency and require extensive land area. This study has constructed a novel overlapping horizontal subsurface flow CWs (OLCWs). Remarkably, OLCWs with mixed lightweight fillers (M-OLCWs) exhibited a significant enhancement in total nitrogen (TN) removal efficiency (88-91 %) in different hydraulic loading rates compared to single filler OLCWs (48-62 %). This significant enhancement can be attributed to the lightweight fillers, which have higher abundances and diversity of nitrogen related microorganisms. The treatment dynamics revealed that the second stage exhibited an excellent TN removal efficiency (73-75 %) attributed to sufficient dissolved oxygen concentration by water drops reoxygenation. The research reveals that M-OLCWs, by utilizing water drops reoxygenation and lightweight fillers, not only enhance pollutant treatment efficiency but also reduce required land area, thereby offering a sustainable solution for rural decentralized wastewater treatment.