(4)Design of a treatment system for leachate from uncontrolled disposal of steel dust on soil

摘要

This paper addresses the design of a treatment system for leachategenerated by the uncontrolled disposal of steel dust on agricultural land.For the development of the methodology presented in this manuscript,columns of glass (6 cm diameter), in which 15 cm of steel dust was used tocover 50 cm of soil, were installed. The columns were irrigated withconstant fluxes of water, equivalent to the average precipitation of theEcuadorian Highland region (0.05 mL/h.cm2). To avoid the “wall effect”,fiberglass (6 cm diameter, 0.8 mm thickness) was used to cover the solids inorder to allow for uniform distribution of the water throughout the column.Leachate was collected every three days during four months andcharacterized by atomic absorption spectrophotometry. Thus, it was foundthat the effluents exceeded the maximum permitted concentration ofchromium and arsenic in Ecuador that can be discharged into freshwaterbodies (0.5 mg/L y 0.1 mg/L respectively). Subsequently, the effluent wasstabilized with cement and lime in liquid/solid ratio of 0.4, 0.5 and 0.6; itwas demonstrated that the liquid/solid ratio of 0.4 and 0.5 allow forobtaining blocks that contain the recommended amount of moisture to beconfined in landfills (10%). Finally, a 2 m3/month capacity treatment systemof was designed based on the results. In this system, the following processwas proposed: Mixing of the leachate in liquid/solid ratios of 0.4 (equivalentto 0.5 relative to cement and 2.0 relative to lime), molding and compactingof the mixture, curing and drying of the blocks every three days andtransportation of the blocks to the landfill. This system requires an initialinvestment of US$ 38,782 and has an operating cost of US$ 803.48.