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

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

Ghent, Belgica

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

Universiteit Gent, Faculty of Bioscience Engineering,

A free water surface wetland (F.W.S.W.) was built to treat wastewater containing metals (Cr, Ni and Zn) and nutrients from a tool factory at Santo Tomé, Argentina. It is 50 m length and 40 m width, with a central baffle dividing it in two sections. Water depth was 0.5-0.8 m and water residence time ranged 7-12 days. The bottom was sealed with bentonite and covered with a layer of the removed soil. Water, sediment and macrophytes were sampled in the inlet and outlet area of the wetland during two years. Eichhornia crassipes became dominant and covered about 80% of the surface throughout the first year, to decrease progressively until its disappearance over the following six months. Water depth was lowered and Typha domingensis steadily increased plant cover to attain 30% of the surface by the end of the study period. T. domingensis reached a higher biomass, density and height in the constructed wetland than in the nearby undisturbed wetland. While E. crassipes was dominant along the first year, the wetland retained 62% of the incoming Cr and 48% of the Ni, nitrate and nitrite were also removed (65 and 78 %, respectively), while i-Pdiss and ammonium were not efficiently removed. Zn was below 50 µg l-1 in both the influent and effluent. The metal content in the sediments did not increase and retention was mediated through macrophytes uptake. Metal content in plant tissue was higher in roots than in the leaves. During the period of E. crassipes decline the wetland retained 49% of the incoming Cr, 45% of Ni, 48% nitrate, 94% nitrite, 58% ammonium and 47% i-Pdiss. Cr, Ni and Zn in the bottom sediments were increased close to inlet but not in the outlet. Since T. domingensis became dominant retention was 58% Cr, 48% Ni and 64% i-Pdiss, while 89% nitrate, 84% nitrite and 13% 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.