Emergency water treatment with combined ferrate(vi) and ferric salts for disasters and disease outbreaks

Abstract

Clean water is vital amid a disaster or disease outbreak-related emergency. This study aimed to evaluate an inventive emergency water treatment (EWT) process with the joint use of ferrate(VI) and ferric salts for production of drinking water in an emergency. Laboratory-scale batch studies were implemented to assess the effects of Fe(VI) : Fe(III) and overall Fe dose on the treatment performance. Results show that the decreasing Fe(VI) : Fe(III) ratio from 2 : 1 to 1 : 1 and 1 : 2 benefited bacterial inactivation, particulate removal, and abatement of aqueous Pb and As, but disfavored Cd alleviation in comparison with ferrate(VI) alone. At Fe(VI) : Fe(III) = 1 : 2, a higher iron dose (1.0–11.0 mg L⁻¹) enhanced the treatment performance. The final pH could be well predicted based on chemical equilibrium calculations collectively governed by the Fe(VI) : Fe(III) ratio, overall Fe dose, initial pH, alkalinity, and atmospheric CO₂ concentration. Afterwards, the combined Fe(VI)/Fe(III)-based EWT was examined in an innovative tea bag treatment design (Fe(VI) : Fe(III) = 1 : 2; total Fe = 11.0 mg L⁻¹), which decreased total coliform (1.12 × 10⁵ MPN per 100 mL) and E. coli (3.65 × 10⁴ MPN per 100 mL) to undetectable levels, lowered the turbidity from 2.00 to 0.39 NTU, and reduced Pb, As, and Cd from 141, 48, and 53 μg L⁻¹ to 8, 2, and 13 μg L⁻¹, respectively. The estimated cost of the tea bag design was approximately $0.017 per 10 L of water, more economically competitive than existing EWT products with similar functions. The combined Fe(VI)/Fe(III) treatment represents an innovative, resilient, viable, and affordable EWT approach. Beyond EWT, the modification of ferrate(VI) treatment finds a new pathway to broader application of ferrate(VI) to municipal water treatment.