How substrate influences nitrogen transformations in tidal flow constructed wetlands treating high ammonium wastewater?

A long-term lab-scale experiment was conducted to investigate the influence of different substrates, namely, zeolite, quartz sand, biological ceramsite, and volcanic rock, on the dynamics of nitrogen transformations in constructed wetlands (CWs) with a tidal operational strategy. The zeolite-based tidal flow ON (TFCW) outperformed the quartz sand, ceramsite, and volcanic-based TFCWs in removing NH4+-N and TN under the same operational conditions. A mean removal rate of approximately 97% for ammonium at an inflow concentration of about 100 mg L-1 was observed in TFCW with zeolite, higher than those of the other three TFCWs (15-34%). This superior performance was due to the competitive properties of zeolite, including its inicropore volume (61.2 mm(3)g(-1)), specific surface area (16.6 m(2)g(-1)), and cation exchange capacity (4.3 cmol kg(-1)). The rapidly developing biofilm in TFCWs with sufficient oxygen supply enveloped the surface of each substrate and filled the micropores, reducing the specific contacting surface area and cation exchange capacity. However, the rapid and stable removal of ammonium can be attributed not only to the high adsorption capacity of the specific substrate during the flooded phase but also to the fast nitrification during the drained phase of each tidal operation, facilitating the regeneration of the adsorption capacity of the substrates. The abundance of specific bacteria depends on various substrates, but the diversity of genes from different substrates is similar. Substrates crucially influence nitrogen transformations in TFCWs treating wastewater, so their selection should be a design criterion. (C) 2014 Elsevier B.V. All rights reserved.