Development of a low-waste technology for arsenic removal from drinking water

The purification of drinking water containing inorganic arsenic compounds causes important problems in Hungary. Arsenic ions are accompanied by high concentrations of ammonium-, Fe-, and Mn-ions, humic acids (about 5-10 mg/l), dissolved gases, and the water has a high temperature, > 30degreesC. This contamination arises from natural leaching of arsenic rocks by the percolating water. New low-waste technology was developed by a combination of ion exchange and adsorption methods. It is appropriate for selective removal of ammonium, iron, manganese, and arsenic ions, as well as humic acids from drinking water. Processes were applied in laboratory and field experiments. Natural ion exchangers and adsorbents were used as sodium-form natural clinoptilolite (Na-Cli), manganese-form natural clinoptilolite (Mn-Cli), granulated activated carbon (GAC), and granulated Al2O3/Fe(OH)(3). Natural zeolite is mined in Hungary and the clinoptilolite content was found to be 65-70 m/m% by XRD analysis. Optimal exhaustion-regeneration cycles were estimated and a pilot-plant set-up was designed. The Na-form of clinoptilolite was produced by 20 BV 20 gNaCl/l solution, then washed with distillated water. The Mn-form was prepared from the Na-form with 20 BV of 1 mol/l MnSO4 and 20 BV of 10 g/l KMnO4. Al2O3/Fe(OH)(3) adsorbent was prepared from granules of 0.3-10 mm of activated Al2O3 and Fe(OH)(3) was freshly precipitated onto the surface of particles. Laboratory and field experiments were carried out by 3.2 cm i.d.*15 cm and 8 cm i.d.*90 cm columns. Adsorption and ion exchange capacities were estimated for all materials. In the model experiments, up to the 10 mug/l As, the adsorption capacities were as follows: Al2O3/Fe(OH)(3), 86.8 mug/g; GAC, 663 mug/g; Mn-Cli, 15.3 mug/g. The experimental set-up proved to be efficient for the removal of all analytes with concentrations higher than the maximum contaminant level (MCL).