Removal of Iron from Groundwater by Direct Filtration through Coal and Carbonaceous Shale

Most commonly employed method of iron removal from groundwater is oxidation-floc formation and involves three basic processes, e.g. oxidation of ferrous iron by aeration, settling of the ferric hydroxide floc, and floc filtration by rapid sand filtration. In adsorption-oxidation (adsorptive filtration) iron removal, the system is operated under anoxic condition suppressing the oxidation of ferrous iron and iron is removed by adsorptive filtration. On exhaustion of the ferrous iron adsorption capacity of the filter media, the anoxic filter bed is regenerated by backwashing the filter bed with oxygen-rich water or with a chemical oxidant. In this study, removal of iron from groundwater by direct filtration through coal and carbonaceous shale under anoxic condition was examined. In batch adsorption test under anoxic condition, 80 g/L of coal or carbonaceous shale removed (adsorbed) 83.8% or 91.7% of ferrous iron from a ground water (total iron 2.66 mg/l; ferrous iron 2.35 mg/L). In a 4-hour laboratory filtration test of the groundwater, effluent iron concentrations were 0.09-0.40 mg/L (ferrous iron) and 0.48-1.01 mg/L (total iron) for the coal filter, and 0.01-0.06 mg/L (ferrous iron) and 0.02-0.20 mg/L (total iron) for the carbonaceous shale filter. In a 4-hour in situ direct filtration test of the ground water, effluent iron concentrations were 0.12-0.42 mg/L (ferrous iron) and 0.77-1.16 mg/L (total iron) for the coal filter, and 0.01-0.05 mg/L (ferrous iron) and 0.03-0.12 mg/L (total iron) for the carbonaceous shale filter. The study indicates that direct filtration through carbonaceous shale is a potentially useful method for adsorptive filtration iron removal from groundwater.