Nutrient and metal removal in a constructed wet land for waste-water treatment from a metallurgic industry.

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

Ecological Engineering

Elsevier

Lugar: Oxford; Año: 2006 vol. 26 p. 341 - 347

0925-8574

The present contribution assesses the nutrient and metal removal in a surface constructed wetland for industrial waste water treatment, compares it with a previous small-scale prototype and discusses the observed differences. The constructed wetland was 50 m length by 40 m width, with a central dike dividing it in two identical sections. Water depth was 0.5-0.8 m and the water residence time ranged from 7 to 12 days. The wetland was rendered impermeable by means of a bentonite layer covered with a layer of the surrounding soil. Several locally available macrophyte species were transplanted into the wetland. 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 14 and 6% cover. The wetland removed 86% of the incoming Cr and 67% of Ni. Zn concentrations were below 50 µg l-1 in most samplings. Metal concentrations in plant tissue were larger in the roots than in the leaves. Metal concentration in the bottom sediment did not increase. Increased concentration in the macrophyte tissue represented the main retention mechanism. Seventy and 60% of the incoming nitrate and nitrite were removed. Large denitrification losses are suggested. The outcoming water was anoxic in most samplings. Soluble reactive phosphorus and ammonium were not retained within the wetland being often higher at the outlet. In a small-scale prototype previously constructed cattail attained luxuriant growth and efficiently removed metals and SRP. Different behaviour between both wetlands is discussed.