Abstract

This research work was dedicated to the problem arising from the coexistence of arsenic and organic substances principally in the US (the Superfund Sites) and Bangladesh. Dissolved organic ions are strong competitors to arsenates, and because of their large size and slow kinetics, arsenic removal becomes problematic. Macroporous ion exchange media can remove both arsenic and organic pollutants efficiently while preserving exchange capacity and effluent quality. The novelty of this work is characterized by the determination of interdependence of important factors influencing the sorption of arsenates and organic substances by macroporous ion exchange media. Exchange capacities of these resins in both chloride and hydroxyl forms in acidic media as well as the chloride-form operating in weakly basic medium were investigated. The investigations were focused on factors such as the effects of pH, influent concentration of dissolved organic matter (DOM) and filtration velocity. Interaction of these effects was also investigated. Reducing the pH from 10.4 to 7.0 increased the arsenate-exchange capacity from 28 meq/kg to 63 meq/kg (a 35 meq/kg increase). Optimum conditions for regeneration of macroporous media have been determined such as a NaCl consumption of 300 kg/tonne, a concentration of NaCl solution of 10%, a ratio of NaCl concentration to that of NaOH in regenerant of 10, a regeneration rate of 4 m/h, and a temperature of 40{493} C. Waste handling processes have been developed to treat and reuse spent regeneration solutions as well as to detoxify the solid waste containing arsenic and organic matter. A reagent based technology for the treatment of spent regeneration solutions by Ca(OH) 2 and MgCl 2 (or MgSO 4 ) has been devised. Based on the results, appropriate decontamination schemes have been developed for groundwater contaminated with arsenic and organic impurities. The benefit of these schemes is guidance for the organization of the treatment process depending upon the levels of mineralization and concentration of DOM as well as the conditions for the implementation of the process (for an existing or new treatment unit to be designed)