Effect of different macrophytes in abating nitrogen from a synthetic wastewater.

In an experiment conducted in an unheated glasshouse from October 2006 to March 2008, the efficiency was studied of different macrophytes in reducing NO3-N and NH4-N concentrations and loads in reconstructed wastewaters. The experimental setup consisted of plastic tanks, filled with gravel and vegetated with Carex elata All., Juncus effusus L., Phragmites australis (Cav.)Trin., Phalaris arundinacea L. var. picta and Typha latifolia L. There was also a control without vegetation. From January to July, a solution of 50-60 ppm of NH4-N and NO3-N was applied monthly, then the input concentration was doubled. The total load at the end of the experimental period was 70.4 g/m2 of NO3-N and 67.3 of NH4-N. At the end of each month, water was discharged from the tanks and analysed to determine the two nitrogen forms. At the end of the experiment, 33 g/m2 of total N (almost 24% of applied N) had disappeared in the control. Among species, the highest abatement was detected in Typha (72 g/m2, almost 52% of applied N), the lowest in Juncus (35%). A weekly chemical analysis in July showed that a large amount of NH4-N quickly disappeared in all treatments, while NO3-N only decreased in the vegetated tanks. In December NH4-N had similar dynamics, while NO3-N increased. All water volumes entering and exiting the tanks were measured in order to evaluate evapotranspiration; Typha showed the highest water consumption, reaching a cumulative value of above 1,000 mm. At the end of the experiment Juncus presented the highest amount of nitrogen stored in the aerial parts (5.63 g/m2) and Typha the lowest (1.92 g/m2), suggesting that the nitrogen disappearance can be related to different microbial activities or a different amount of nitrogen stored in belowground biomass.