Kinetics and oxidative mechanism for H₂O₂-enhanced iron-mediated aeration (IMA) treatment of recalcitrant organic compounds in mature landfill leachate

A hydrogen peroxide (H₂O₂)-enhanced iron (Fe⁰)-mediated aeration (IMA) process has been recently demonstrated to effectively remove organic wastes from mature landfill leachate. In this paper, the kinetics and oxidative mechanisms of the enhanced IMA treatment were studied. Bench-scale full factorial tests were conducted in an orbital shaker reactor for treatment of a mature leachate with an initial chemical oxygen demand (COD) of 900-1200 mg/L. At the maximum aeration rate (8.3 mL air/min mL sample), process variables significantly influencing the rates of H₂O₂ decay and COD removal were pH (3.0-8.0), initial H₂O₂ doses (0.21-0.84 M), and Fe⁰ surface area concentrations (0.06-0.30 m²/L). Empirical kinetic models were developed and verified for the degradation of H₂O₂ and COD. High DO maintained by a high aeration rate slowed the H₂O₂ self-decomposition, accelerated Fe⁰ consumption, and enhanced the COD removal. In hydroxyl radical (OH{radical dot}) scavenging tests, the rate of removal of glyoxylic acid (target compound) was not inhibited by the addition of para-chlorobenzoic acid (OH{radical dot} scavenger) at pH 7.0-7.5, ruling out hydroxyl radical as the principal oxidant in neutral-weakly basic solution. These experimental results show that this enhanced IMA technology is a potential alternative for the treatment of high strength recalcitrant organic wastewaters.