Treatment and transport modeling of landfill leachate contaminants in an engineered wetland system.

Although an essential micronutrient, boron becomes toxic at concentrations slightly above the optimum range. The use of an engineered wetland system consisting of a peat filter and a surface water wetland for treatment of landfill leachate was investigated. Laboratory tests showed that boron is mainly present in inorganic form. Adsorption of boron by peat was a fast process and virtually complete within 2.5 hours. Drying of peat (at 105°C, 90°C, 75°C, and air drying), pH, temperature, and solution composition had a significant effect on boron adsorption while shaking and solution-to-soil ratio did not have any significant effect on boron adsorption by peat. Also, the presence of other anions such as SO4 -, Cl- or combination of both in synthetic solution made from boric acid had no significant effect on boron adsorption by peat. Maximum adsorption of boron on peat occurred at a pH around 9. Addition of lime, optimum ratio being 1 g lime to a 100 g peat, enhanced boron adsorption capacity of peat by 50--100%. Adsorption of boron decreased with temperature increase. Boron desorption showed hysteresis as only 24% to 45% of adsorbed boron was released into the solution when subjected to desorption test. A second-order design model for adsorption of boron by peat was developed, which incorporates the effect of pH and temperature. Adsorption capacity of peat was directly related to organic matter content and showed a positive effect, i.e. boron adsorption increased with organic matter content increase. Amberlite resin was far superior to peat and other organic material in adsorbing and removing of boron from leachate. Peat also proved to be effective in removing metals such as iron, lead, and zinc from landfill leachate. A new transport code (in Fortran), SOLTRAN, was developed which has the capability of handling non-linear adsorption isotherms. An engineered wetland system consisting of a peat filter followed by a free water surface wetland at Huneault Waste Management landfill, Ontario, was used as a case study. It was demonstrated that peat filter can effectively treat landfill leachate. (Abstract shortened by UMI.