Removal efficiency in a constructed wetland for waste-water treatment from a metallurgic industry

MAINE A,; HADAD H,; G, SANCHEZ; S, CAFFARATTI; BONETTO, C

Lisboa

Conferencia; 10th International Conference on Wetland Systems for Water Pollution Control.; 2006

Wetland Systems for Water Pollution Control.

A free water surface wetland (F.W.S.W.) was built to treat wastewater containing metals (Cr, Ni, Zn, Fe) and nutrients from a tool factory in Santo Tomé, Argentina four years ago. It is 50 m long and 40 m wide, with a central baffle dividing it in two sections. Water depth was 0.5-0.8 m and water residence time ranged from 7 to 12 days. Water, sediment and macrophytes were sampled in the inlet and outlet area of the wetland during four years. Three successive phases of vegetation development were observed and three different patterns of metal retention were attained. During the E. crassipes dominance, metals were retained in the macrophyte biomass; during E. crassipes + T. domingensis stage, metals were retained in the sediment, and in the T. domingensis dominance stage, metals were retained in sediment and in the macrophyte biomass. Removal efficiencies did not present significant differences among the three vegetation stages, being 49.0-66.5 of the incoming Cr, 48.1-73.0 % Ni, 64.8-82.4 % Fe, 61.7-86.1 % NO3-, 62.0-86.4 % NO2-. BOD and COD decreased 55.0-67.8 % and 54.4-68.3, respectively. i-Pdiss and NH4+ were not efficiently removed. The biomass N pool represented less than 25% of the N removed from the incoming wastewater, denitrification represented the major N removal process. 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.