Heavy metals removal from wastewater by peat absorption.

Abstract

A constructed wetland is an effective method to remove oil, organic matter, nitrogen, phosphorus and heavy metals from wastewater. Peat is a polar and highly porous plant material formed in wetland areas. Removal of oil, color and treatment of domestic wastewater by peat have been well documented. The mechanisms of pollutant removal by peat include adsorption, complexation, ion exchange and precipitation. Limited research indicates the feasibility of the removal of heavy metals by peat. The primary objective ofthis project was to study the peat adsorption of several heavy metals from wastewaters such as landfill leachate and acid mine drainage in which large amounts of heavy metals are typically present. Copper, nickel and zinc were chosen to represent heavy metals in this study. A series of batch studies were performed to test the peat adsorption capacity of heavy metals. Peat was used as the adsorbent and copper, nickel and zinc, and a mixture of the three metals, were used as the adsorbates. It was found that the three metals were strongly adsorbed by peat, and that adsorption generally followed the Langmuir isotherm and/or the Freundlich isotherm. A dynamic column experiment was conducted by feeding solutions containing fixed concentrations of the mixture of copper, nickel and zinc through a peat column. A continuous removal of98% of each heavy metal was achieved throughout 66 day column experiment. A chemical equilibrium model (MINTEQA2) was also applied in the project. It was found that the potential for precipitation existed in a buffered column feed solution but not in an unbuffered feed solution. The model also indicated that heavy metals removal was possibly hindered by the complexation with dissoloved organic matter (DOM).