The study of constructed wetland in removal of chromium by Phragmitis australis plant (Case study: Birjand City)

The aim of this study was to evaluate the performance of Horizontal Sub-Surface Flow Constructed Wetland (HSSFCW) for the removal of Cr by Phragmitis australis and to assess the effect of the plant, bed material, hydraulic loading rate and hydraulic retention time on system performance. In this study, 12 cells of pilot system were built in parallel way and in dimensions of 50 × 75 × 200cm at the end of water treatment plant in Birjand University. Temperature and pH were same in all the cells. The results showed that the removal of Cr in cells containing plants was higher than cells without Phragmitis australis. Change of the bed material from coarse texture to fine-grained texture will make significant increase in the average percentage of Cr removal(the removal percent insamedischarge 100(l/d), in fine and coarse-textured plant cells was%31.87 and %24.61respectively and inlack ofplantscells,with fine and coarse textures was%31.25 and %14.92, respectively). By increasing the retention time of 1 to 5 days, Cr concentration and consequently the removal rate were increased. These results are indicative of the positive effect of HSSFCW system in the presence of Phragmitis australis in removal of heavy metals such as Cr, therefore to remove heavy metals from wastewater, cultivation ofPhragmitis australis and fine-grained texture is recommended.