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

Abstract

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 northeast 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—2 × 2 design and two composed of three lines of elements—2 × 3 design). Different macrophyte species were used (Phragmites australis, Carex elata, Juncus effusus, Typha latifolia, Chrysopogon zizanioides, Sparganium erectum, and Dactylis glomerata). The floating systems were easily installed and required few maintenance operations. Native plants grew successfully, developing roots 90–135 cm deep 1 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 2 × 3 design had a slightly better performance than 2 × 2 in reducing COD (38 and 28% of removal, respectively). The two designs performed similarly on NO3-N, reducing the incoming concentrations by 12% (2 × 3 design) and 14% (2 × 2). This form of nitrogen represents almost all the total nitrogen, which was abated by 13% by the 2 × 3 design and by 29% by 2 × 2 design.