Degradation of propylene glycol wastewater by Fenton's reagent in a semi-continuous reactor

Propylene glycol (PG) wastewater seriously threatens aquatic lives and causes health damage to human beings. Several early studies for PG degradation focused on biological process, which usually proceeds at a slow rate and is often inhibited by substances which are toxic to the microorganisms. In this paper, Fenton method was exploited for treating PG wastewater in a semi-continuous reactor with adding ferrous sulfate (FeSO4) and hydrogen peroxide (H2O2) to the reactor, respectively. Semi-continuous applications of H2O2 and Fe2+ could result in low steady state of HO, which would minimize HO scavenging and further increase PG oxidation efficiency. Under the optimal conditions, 99.1% of PG conversion and 88.4% of COD removal were achieved. In addition, pseudo-first-order model, in which the concentration of HO was assumed to remain constant, was established. The intrinsic activation energy of HO with PG, calculated by Arrhenius-equation was 35.18 kJ/mol. The intrinsic reaction rate constant of HO with PG around optimal conditions was 1.56–1.72 × 108 M−1 s−1. After Fenton's reaction, PG molecules could not be thoroughly oxidized to H2O and CO2. Intermediates, such as aldehyde, acetone, methanol, formic acid, and acetic acid, were checked by GC–MS, which all had a very low content and toxicity. As a homogeneous catalytic oxidation, Fenton oxidation is a feasible treatment for PG wastewater for its low toxicity, low price, and high efficiency.