Metal and nutrient removal in a constructed wetland for industrial wastewater treatment in Argentina.

MAINE, A; HADAD, H; SUÑE, N.; SANCHEZ, H.; CAFFARATTI, S; BONETTO, C

Wetlands: Ecology, Conservation and Restoration

Nova Science Publishers.

Lugar: New York; Año: 2009; p. 97 - 131

This chapter summarizes the nutrient and metal removal of a free water surface constructed wetland and compares it with a previous small-scale prototype. The wetland was built to treat wastewater containing metals (Cr, Ni, Zn) and nutrients (P and N) from a tool factory in Santo Tomé, Santa Fe, Argentina. Water, sediment and macrophytes were sampled at the inlet and outlet areas of the constructed wetland during three years. Both wetlands showed high efficiencies in contaminant removal. The development of the vegetation showed the same pattern in both the small-scale prototype and the large-scale wetland. Three successive phases of vegetation dominance were developed and three different patterns of contaminant retention were observed. A first phase of floating macrophyte colonization with dominance of Eichhornia crassipes was followed by a combined floating-emergent phase ending in an long, on-going stand of emergent macrophyte phase, with dominance of Typha domingensis. During the E. crassipes dominance, contaminants were retained in the macrophyte biomass; during the E. crassipes + Typha domingensis stage, contaminants were retained in the sediment and in the T. domingensis dominance stage, contaminants were retained in sediment and in the macrophyte biomass. Even though retention mechanisms were different, removal efficiencies did not show significant differences among the three vegetation stages, except for NH4+ and soluble reactive phosphorus (SRP). Greenhouse experiments were carried out to explain the early disappearance of floating macrophytes. Thresholds for conductivity, pH and metal damage were determined. High conductivity and pH of the incoming wastewater were the cause of the disappearance of the floating species. Because of its highest tolerance, T. domingensis is the best choice to treat wastewater of high pH and conductivity with heavy metals, a common result from many industrial processes.