pH-conditioning for simultaneous removal of arsenic and iron ions from groundwater

The effects of some commonly used pH conditioners, viz., lime, banana ash, the carbonate and the bicarbonate of sodium and potassium and their binary mixture, on simultaneous removal of arsenic and iron ions from water have been studied. KHCO3 has been found to be the most suitable pH conditioner for the purpose. About 80 mg/L KHCO3 can remove both arsenate and iron ions from initial 250 μg/L and 20 mg/L to below their respective guideline values of the WHO for drinking water, retaining the final pH in the acceptable range for drinking. The simultaneous removal of arsenate and iron by the pH-conditioners decreases in the order: Lime > KHCO3 > NaHCO3 > K2CO3 > Na2CO3 > ash. However, lime requires post-treatment correction of highly alkaline pH. The arsenate ion is removed predominantly through goethite or ferrihydrite in the presence of the bicarbonates and through ferric hydroxide in the presence of the more alkaline pH-conditioners. KHCO3 is more advantageous over the more basic substances including NaHCO3, because with it, one not only needs the smallest dose but also can avoid careful adjustment of the dose for regulating the initial and the final pH. The paper clearly demonstrates the potential of KHCO3 to substitute the currently used pH-conditioners, viz., ash, lime and NaHCO3 for simultaneous removal of arsenate and iron ions.

► KHCO3 should provide the best pH for simultaneous As and Fe ion removal methods.
► KHCO3 is better than the commonly used pH conditioners, viz., ash, lime and NaHCO3.
► Adjustment of final pH is not required in case of KHCO3 and NaHCO3.