Behavior of Zinc in a Constructed Wetland System Receiving Domestic Wastewater

Abstract

In Japan, environmental quality standards for Zn pollution were enacted recently because of the toxicity of Zn to aquatic ecosystems. A free-water-surface constructed wetland (500 m²) planted with Zizania latifolia Turcz. received secondary-treated wastewater from a dormitory (60 to 100 residents) at the Koibuchi College of Agriculture and Nutrition in Japan, to remove nutrient salts before the discharge of the water to a pond for agricultural use. We examined the removal efficiencies of Zn and its behavior in this constructed wetland within 3 years and discussed the mechanism of Zn removal. The constructed wetland was effective in treating wastewater with low Zn concentrations. The T-Zn concentration in secondary-treated domestic wastewater (average T-Zn: 0.048 mg/L) decreased by 51% during passage through the constructed wetland. Most of the dissolved Zn was removed, but only a little particulate Zn was removed. The increase in Zn concentration in the wetland soil corresponded to 69.8% of the Zn removed by the wetland. However, the amount of Zn accumulated in the aboveground parts of Z. latifolia corresponded to only 9.8% of the Zn removed by the wetland. Thus, Zn was removed mainly by adsorption onto the wetland soil, including soil particles and organic matter.