Decontamination of landfill leachate by soils with different textures.

Soils with different textures (sandy, loamy, and clay soils) were used as filters to attenuate leachate from the Gin Drinkers' Bay landfill. They were used to pack columns of different depths: 0.2, 0.6, and 1.0 m. Eight millimeters of leachate was drained into the soil columns each day for 56 days. The percolated leachates were collected weekly and their properties analyzed. It was revealed that the properties became rather stable at Day 28 and therefore only the data from Day 28 are presented. The effluents from the loamy and clay columns with depths of 0.6 and 1.0 m contained significantly lower (P less than 0.05) ammonia contents and had lower chemical oxygen demand than those from sandy soil columns. Moreover, the depth of the columns of loam and clay did not show a significant difference (P greater than 0.05). Sandy soil was the least effective in attenuating the leachate. The efficiency of all the soil columns decrease as the soil depth decreased. It was also noted that growing of tree seedings (Acacia confusa) could further improve the efficiency of the loamy soil, especially for the removal of Na. The phytotoxicity of the raw and percolated leachate was evaluated using seed germination of two plant species (Brassica chinensis and Lolium perenne) and the growth of an uncellular green alga (Chlorella pyrenoidosa). In general, the raw leachate was toxic and inhibited seed germination and root growth of the two plant species and the growth rate of the unicellular green alga. The toxicity was due to the high levels of ammonia-nitrogen. COD, iron, manganese, and sodium ions. Percolated leachate, especially from loamy and clay soil columns, exhibited a decrease in phytotoxicity. Clay or loamy soil columns of 0.6-m soil depth seemed to be sufficient to remove the phytotoxic substances in landfill leachate.