Growth and biomass production of different plant species in two different constructed wetland systems in Sicily

Constructed wetlands (CWs) could play a strategic role in wastewater reclamation and reuse in arid and semiarid regions, such as the Mediterranean area. The aim of this study was to analyse the phytoremoval effectiveness of Phragmites australis and spontaneous plant species (SPS) in two CW systems: a horizontal (H-SSF) and a vertical (V-SSF) subsurface flow. P. australis showed a higher biomass growth than SPS and always covered 100% of the bed’s surface. The H-SSF system was more suitable for enhancing biomass growth of P. australis (4701 g mÀ2 as compared to 3088 g mÀ2 detected in the V-SSF CWs) whereas V-SSF of SPS (1700 g mÀ2 and 100% total cover as compared to 240 g mÀ2 and 40% total cover observed in H-SSF). SPS included species belonging to different botanical families in relation to the system adopted. Some of these species (i.e. Phalaris spp. and Chrysantemum segetum) were dominant in aboveground floral composition. Beds with SPS showed the same efficiency of the Phragmites ones in TSS, COD and pathogen removal. Phragmites was more effective than SPS in removing BOD5 (in horizontal system), total phosphorus and nitrates. V-SSF system was more effective than H-SSF in removing total nitrogen. SPS presence did not decrease the efficiency of unplanted beds. Irrespective of the different plant species covering the beds, CWs were overall efficient in removing pollutants confirming their potential as an economic alternative to traditional urban wastewater treatments in small and medium-sized communities.

In the first and second stages, P. australis developed greater biomass than SPS and covered 100% of the bed surface. The H-SSF was more suitable for P. australis, while V-SSF for SPS (100% covered surface) provided more suitable root aeration conditions for these plants. SPS belonging to different botanical families grew in unplanted beds. Among the recognized species grown in the vertical bed, Phalaris spp. and Chrysantemum segetum showed the highest incidence on floral composition. SPS showed the same efficiency in TSS, COD and pathogen removal as Phragmites. Common reed, however, was more effective than SPS in removing BOD5 (in horizontal system), total phosphorous and nitrates, which may otherwise pollute surface and ground waters. The V-SSF was more effective than the H-SSF in removing total nitrogen. The SPS development did not decrease the efficiency of unplanted beds. Knowledge gained regarding the interaction of the plant–phytodepuration system (horizontal or vertical) can be used to improve phytoremoval efficiency and to reduce CW management costs. Regardless of the plant species covering the beds, the pilot plant was efficient in removing some pollutants and confirmed the potential of CWs as an economic alternative to conventional urban wastewater treatment technologies in small and medium-sized communities. Further improvement in the CW systems is requested by Italian regulation (DM 185/03) for microorganism removal (Escherichia and Salmonella) when CW effluents are reused for irrigation.