Sequestration of Iron in Groundwater by Polyphosphates

Abstract

For small communities, iron removal from groundwater by conventional methods is sometimes cost prohibitive. An experimental investigation was conducted to determine the effectiveness of sequestering this iron by polyphosphate addition while providing the necessary disinfection through chlorine addition. Iron sequestration by polyphosphate was found favorable to no iron treatment. The presence of calcium in the groundwater models inhibited treatment effectiveness. The polyphosphate sequestrant should be added to the groundwater before the addition of chlorine but simultaneous addition was nearly as successful. The commercial polyphosphates analyzed were not found to depolymerize significantly at 18 °C during typical drinking water supply storage time periods. Treatment was found to be better with the polyphosphate product containing a higher percentage of polyphosphate relative to total phosphorous. Ultrafiltration results suggest that much if not all the sequestered iron is in a colloidal or polymeric form.