Effect of different macrophytes in abating nitrogen from a synthetic wastewater

Abstract

An experiment conducted in an unheated glasshouse from October 2006 to March 2008 studied the efficiency of different macrophytes in reducing NO 3-N and NH 4-N concentrations and loads in synthetic wastewaters. The experimental setup consisted of plastic tanks, filled with gravel and vegetated with Carex elata All., Juncus effusus L., Phragmites australis (Cav.) Trin., Typhoides arundinacea L. Moench (syn 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 NH 4-N and NO 3-N was applied monthly; then the input concentration was doubled. The total load at the end of the experimental period was 70.4 g/m 2 of NO 3-N and 67.3 of NH 4-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/m 2 of total N (almost 24% of applied N) had disappeared in the control. Among species, the highest abatement was detected in T. latifolia (72 g/m 2, almost 52% of applied N) and the lowest in J. effusus (35%). A weekly chemical analysis in July showed that a large amount of NH 4-N quickly disappeared in all treatments, while NO 3-N only decreased in the vegetated tanks. In December, NH 4-N had similar dynamics, while NO 3-N increased. All water volumes entering and exiting the tanks were measured in order to evaluate evapotranspiration. T. latifolia showed the highest water consumption, reaching a cumulative value of above 1000 mm. At the end of the experiment, J. effusus presented the highest amount of nitrogen stored in the aerial parts (5.63 g/m 2) and T. latifolia the lowest (1.92 g/m 2).