Water disinfection using hydrogen peroxide with fixed bed hematite catalyst - kinetic and activity studies

Abstract

A lab-scale reactor with a fixed-bed hematite catalyst for the effective decomposition of H₂O₂ and bacteria inactivation was designed. The bactericidal effect is the largest at a low initial bacterial count of 2·10³ CFU/L, which is typical for natural surface waters. When using a 5 mM H₂O₂ solution and a residence time of 104 min, the reduction in the number of E. coli bacteria is about 3.5-log. At a higher initial bacterial count of 1-2·10⁴ CFU/L, a 5 mM H₂O₂ solution reduces the bacteria number by about 4-log. The H₂O₂ decomposition follows the log-linear kinetics of a first-order reaction while the bacterial inactivation does not. The kinetics of bacterial inactivation was described using the Weibull model in the modified form: log₁₀(N₀/N) = b · tⁿ. The values of the non-linearity parameter n were found to be lower than 1, indicating that bacterial inactivation slows down over time. With increasing initial H₂O₂ concentration, the rate parameter b increases while the non-linearity parameter n decreases. With increasing temperature, both parameters increase. The stability of the catalyst has been proved by XRD, FTIR, SEM, and ICP-OES. The concentration of iron leaching into water during disinfection is much lower than the limit declared by WHO for iron in drinking water. The results show that technical-grade hematite is a promising Fenton-like catalyst for water disinfection. The fixed-bed reactor can be the basis of the mobile installations for water purification in emergencies.

Keywords: Bacteria inactivation; Fenton-like catalyst; Hematite; Water treatment; Weibull model.