Recirculation or artificial aeration in vertical flow constructed wetlands: A comparative study for treating high load wastewater

Intermittently recirculated and aerated VSSF constructed wetland. [Display omitted] •Recirculation and aeration applied in vertical subsurface flow constructed wetlands.•High removal of COD, TKN, and TN, especially in the aerated and recirculated system.•Simultaneous nitrification/denitrification in the aerated and recirculated wetland.•The surface area requirement could be reduced from 3.6 to 1.5m2/person equivalent. Vertical subsurface-flow constructed wetlands at pilot-scale have been applied to treat high hydraulic and organic loads by implementing the following configurations: (1) intermittent recirculation of the treated wastewater from the bottom to the top of the bed, (2) intermittent artificial aeration supplied at the bottom of the bed and (3) the combination of both. These configurations were operated with a saturated bottom layer for a 6h-treatment phase, followed by a free drainage phase prior to a new feeding. COD removal efficiency was 85–90% in all the configurations and removed loads were 54–70gCODm−2d−1. The aerated and recirculated wetland resulted in a higher total nitrogen removal (8.6gNm−2d−1) due to simultaneous nitrification/denitrification, even in the presence of intermittent aeration (6.8Nm3m−2d−1). The extra investment needed for implementing aeration/recirculation would be compensated for by a reduction of the surface area per population equivalent, which decreased to 1.5m2/PE.