A new Constructed Wetland design for enhanced nitrogen recovery, footprint reduction and process intensification

Nutrient recovery is a way to reduce water scarcity. Constructed Wetlands (CW) could be of interest to manage and recover nitrogen from high-load composting leachates. However, they require large treatment area which limits their spread to industries lacking available surfaces. In this study, a Verticalized SubSurface Flow constructed Wetland (VSSFW) offering 2.7 m² of treatment surface on 0.9 m² footprint was designed and compared to a 0.75 m² footprint Vertical Flow Constructed Wetland (VFCW) of same packing-bed volume using a test solution simulating diluted composting leachates. The VSSFW showed higher performances for reducing NH4-N and P concentrations (RE (%) = 98.3 and 95.3 % respectively), and converting NH4-N to NO3-N (conversion rate of 1 : 0.56) than the VFCW (RE (%) = 59.2 and 46.3 % respectively, conversion rate of 1 : 0.14). The nitrate-concentrated solution obtained after treatment held 2.95 / 110 / 19.5 mg .L-1 NH4-N / NO3-N / P concentrations and could have interest for uses as fertilizer and hydroponic feeding solution. Intensification techniques in the form of microbubbles aeration and addition of external carbon (CaCO3) were afterward applied on the VSSFW. The intensified VSSFW showed higher performances (RENH4-N (%) = 97.5 % in 24h only, conversion rate 1 : 0.91), and a quicker production of final nitrate-concentrated solutions. The intensified VSSFW performed 16.5 times higher than the average CW.