Enhanced utilization of oxidants for in situ chemical oxidation of chlorinated and aromatic hydrocarbons

Potentially viable strategies were sought for enhanced utilization of potassium permanganate (KMnO4) and Fenton\u27s reagent during in situ chemical oxidation (ISCO). An innovative concept of controlled release of oxidant was introduced and organic-coated, completely or partially microencapsulated KMnO4 (MEPP) particles (874 ± 377 μm) were created to serve a material that can be specifically targeted to a contaminant source zone. Paraffin wax was employed as the coating material because it is biodegradable, inert to KMnO4, insoluble in water and yet soluble in hydrophobic contaminants such as perchloroethylene (PCE). KMnO4 was released very slowly into water, but the oxidant was rapidly released into PCE. The estimated times for 90% release of the oxidant were 1.6 months, 19.3 years, and 472 years for paraffin wax to KMnO4 mass ratios of 1:1, 2:1 and 5:1, respectively. The MEPP particles preferentially accumulated at the PCE-water interface, and the KMnO4 was rapidly released into PCE (\u3c3 min) as the paraffin wax completely dissolved. These findings suggest that enhanced contact between the target contaminant and the locally high concentrations of KMnO 4 could be achieved at the interfacial region between PCE and water. Fenton\u27s oxidative destruction was investigated for aromatic hydrocarbons (benzene, toluene, ethylbenzene, and o-xylene; BTEX) present as dissolved and adsorbed phases, and chlorinated hydrocarbon (PCE) present mostly as dense non-aqueous phase liquid (DNAPL) (\u3e93% of total PCE mass) in batch reactors (soil: solution = 1 g/L). An enhanced mass removal was observed by combining 300 mM H2O2, 2 mM Fe(III) and 2 mM N-(2-hydroxyethyl)iminodiacetic acid (HEIDA) at near-neutral pH. The PCE degradation was maximal at 600 mM H2O2, 5 mM Fe(III) and 5 mM HEIDA at pH 3. The observed BTEX mass removal rate constants (3.6–7.8 × 10−4 s−1) were compared to the estimated ones (4.1–10.1 × 10−3 s−1) using a semi-quantitative kinetic model. The model sensitivity analyses indicate that iron oxides and soil organic matter could play important roles in the non-specific losses of both H 2O2 and ·OH. These findings suggest that system design could be optimized with respect to process variables in remediation of contaminated soils and groundwater with Fenton\u27s reagent