| This study evaluated the use of an integrated system consisting of two passive technologies (constructed wetland and limestone/sandstone filter) for the treatment of landfill leachate. It included both field and laboratory studies.; The effectiveness of constructed wetland for treating landfill leachate was evaluated over two years. Increasing the number of cells in the constructed wetland from 4 to 9 and the level of plant establishment in the second year improved the removal efficiencies for Fe, Mn, ortho-PO4, TKN, NH 4-N, NO3-N, COD, TSS and TDS by 29.68, 7.30, 33.3, 33.3, 30.6, 8.00, 26.7, 52.2, 43.5 and 54.1%, respectively. Although the ten plants (wool grass, soft rush, tweedy's rush, pickerelweed, yellow-green sedge, fowl mannagrass, soft stem bulrush, fringed sedge, reed canary grass and broad leaf cattail) used in the constructed wetland were excellent accumulators of Fe (8690--23725 mg/kg), they did not accumulate high concentrations of Mn (554--3370 mg/kg) due to Mn Fe antagonism. The roots of the plants accumulated significantly greater concentrations of Fe than the shoots and flowers while the leaves and flowers accumulated significantly greater concentrations of Mn than the roots.; A laboratory experiment, in which two facultative (Woolgrass, Soft stem bulrush) and two obligate (Broadleaf cattails, Soft rush) wetland plants were planted, was used to provide a better understanding of the removal mechanism and the factors affecting removal efficiency. The plant type, time and initial concentrations of heavy metals have significant effects on the removal efficiency of the heavy metals. The Fe, Mn and Zn concentrations in the plant tissues were directly proportional to their initial concentrations in the wastewater. A first-order kinetic model was used to determine Fe, Mn and Zn uptake parameters by wetland plants.; Laboratory experiments were performed to assess the ability of limestone and limestone/sandstone filters to treat landfill leachate. The results showed that the limestone and the limestone/sandstone filters removed 96% and 70% of the Fe and Mn from solution under batch condition in the first 20 and 50 minutes, respectively. The dissolution of CaCO3 and the precipitation of Fe and Mn were affected by temperature and time. As temperature decreased from 20 to 5°C, the removal efficiencies decreased from 99.77 to 94.85% and from 86.11 to 58.00% for Fe and Mn, respectively. The Fe and Mn removal rate constants of the limestone filters were higher than those of the limestone/sandstone. The effluent from continuous flow filters contained on average less than 0.66 mg/L of Fe and 0.47 mg/L of Mn. A mathematical model was developed and used to predict the Fe and Mn concentrations in the outlet of a continuous flow limestone/sandstone filter. Two limestone filters were designed and the various dimensions of the filters were calculated. |
