Cr(VI) is toxic and carcinogenic, which fuels discussions on reducing existing standards for maximum Cr concentrations in drinking water. Fe(II) reductive precipitation is a common and economical method for achieving very low Cr(tot) concentrations (50 mg/L Fe(III)) mitigated the negative impacts of NOM on Cr(VI) reduction and Cr(III) removal. However, even 100 mg/L Fe(III), the highest applied sludge concentration, did not lead to a decrease in Fe(II) dosing requirements under the given conditions. A molar ratio higher than the given stochiometric ratio of [Fe(II)]:[Cr(VI)] = 3 was necessary for sufficient Cr(VI) removal.
