Performance of a floating treatment wetland for in-stream water amelioration in NE Italy

Floating treatment wetlands are innovative systems and their processes are still scarcely known within the traditional methods of phytodepuration. To gain initial information on their performance and potential in removing pollutants two experiments have been conducted in north-east Italy, in a Natural Park with resurgent water. Barriers formed by a new patented floating element were tested in real climatic and water flow conditions. One experiment was conducted in a channel receiving aquaculture effluents, while the other was set in two cleaner channels to test two installation designs (two barriers composed of two lines of elements -2X2 design- and two composed of three lines of elements -2x3 design-). Different macrophyte species were used (Phragmites australis, Carex elata, Juncus effusus, Typha latifolia, Chrysopogon zizanioides, Sparganium erectum, Dactylis glomerata). The floating systems were easily installed and required few maintenance operations. Native plants grew successfully, developing roots 90-135 cm deep one year after planting. Conversely, Chrysopogon zizanioides showed scarce adaptation to local conditions. In the first experiment median chemical oxygen demand (COD) in water passing through the floating wetland system was reduced by 66%, biochemical oxygen demand by 52%, and total phosphorus by 65%. In the second experiment the 2x3 design had a slightly better performance than 2x2 in reducing COD (38% and 28% of removal respectively). The two designs performed similarly on NO3-N, reducing the incoming concentrations by 12% (2x3 design) and 14% (2x2). This form of nitrogen represents almost all the total nitrogen, which was abated by 13% by the 2x3 design and by 29% by 2x2 design.