Multistage hybrid constructed wetland for enhanced removal of nitrogen

Hybrid constructed wetlands (HCWs) are very efficient in removal of total nitrogen. So far hybrid-constructed wetlands have been composed of various combinations of wetland units but most common combination is vertical flow-horizontal flow system. Also, multistage HCWs have recently been used. The present study describes the use of three-stage HCWs for treatment of municipal sewage. The system consists of saturated vertical flow, free-drain vertical and horizontal flow units in series. The experimental system with a total surface area of 10.1 m(2) has been operated for 19 months between March 2009 and October 2010. The results proved that multistage hybrid constructed wetland was able to remove efficiently organics, suspended solids and nitrogen. The overall removal efficiency amounted to 92.5%, 83.8%, 96.0%, 88.8% and 79.9% for BOD5, COD, TSS, NH4-N and TN, respectively. The aerobic vertical flow stage provided high degree of nitrification (removal rate of 4.17 g NH4-N m(-2) d(-1)) while remaining anaerobic stages (first and third) provided suitable conditions for denitrification (removal rates of 0.83 g N-NO3 m(-2) d(-1) and 0.47 g N-NO3 m(-2) d(-1), respectively). The outflow NH4-N concentrations were below 5 mgl(-1) throughout the monitored period including winter period when the air temperature dropped below -20 degrees C. Plant biomass sequestered 28% and 26% of phosphorus and nitrogen inflow load, respectively. (C) 2015 Elsevier B.V. All rights reserved.