Plant growth and removal efficiency in a constructed wetland for wastewater treatment from a tool industry.

MAINE, M. A.; SUÑE, N.; HADAD, H. R.; SÁNCHEZ, G.; BONETTO, C.

Ghent, Bélgica

Simposio; International Symposium on Wetland Pollutant Dynamics and Control.; 2005

Universiteit Gent, Faculty of Bioscience Engineering, WETPOL.

A free water surface (F.W.S) wetland was built to treat waste water enriched with metals (Cr, Ni and Zn) and nutrients from a tool factory at Santo Tome, Argentina. It is 50 m length and 40 m width, with a central dike dividing it in two sections. Water depth was 0.8 m and water residence time ranged 7 -12 days. The bottom was sealed with bentonite and covered with a layer of the removed soil. Operation started on Feb. 2003. Several locally common macrophyte species were transplanted. Eichhornia crassipes (water hyacinth), showed fast growth and soon became dominant attaining 80% cover of the wetland surface. Typha dominguensis (cattail) and Pontederia cordata (pickerelweed) developed as accompanying species attaining 7 and 5% cover. Since Dec. 2003 onwards E. crassipes declined progressively until disappearance in July 2004. The wetland was emptied and more soil was added to the bottom in August 2004. Cattail increased plant cover since then to attain 30% of the wetland surface in Dec. 2004. While water hyacinth was dominant along the first year, the wetland retained 85% of the incoming Cr and 64% of the Ni, nitrate and sulfate were also removed (82 and 57% respectively), while SRP and ammonium were higher in the outlet than in the inlet. Zn was below 50 µg in both the inlet and outlet. The metal content in the sediments did not increase and retention was mediated through macrophyte absorption. Metal content in plant tissue was higher in the roots than in the leaves. During the period of water hyacinth recede the wetland retained 50% of the incoming Cr, 70% of Ni, 75% nitrate, 27% sulfate, 45% ammonium and 72% SRP. Cr, Ni and Zn in the bottom sediments were increased close to inlet but not in the outlet. Since cattail became dominant retention was 8% Cr, 43% Ni and 61% SRP, 79% nitrate 55% sulfate and 19% ammonium were removed. Metals and P in the bottom sediments were strongly increased close to the inlet and in a smaller proportion also in to the outlet. Different trends in coincidence with the vegetation development are discussed.