Comparison of hydrogen peroxide-based advanced oxidation processes for the treatment of azole-containing industrial wastewater

In this study the effectiveness of three types of advanced oxidation processes (AOPs), namely the Fenton, UV/Fenton and UV/H2O2 processes, were compared for the treatment of a lab-prepared wastewater containing five-membered heterocyclic pyrazole, 2-(2-aminoethoxy) ethanol (also known as diglycolamine or DGA), hydrogen peroxide, and inorganic fluoride which are common components of semiconductor wastewater. The Fenton, UV/Fenton (at acidic and near neutral pH) and UV/H2O2 processes with same iron (or no iron) and H2O2 dosing were compared and the results show the three AOPs can remove pyrazole and DGA from the synthetic wastewater rapidly with a simultaneous reduction of total organic carbon (TOC). The UV/Fenton process at initial pH of 8.3 outperformed the other AOPs in terms of overall removal rate due to the synergistic effects of pH-dependent speciation of pyrazole and DGA, direct photolysis of hydrogen peroxide, iron-peroxide complexation and iron-oxalate complexation. The UV/Fenton process at initial pH = 3.0 had the slowest kinetics and the UV/H2O2 process (at pH = 8.3) had the lowest TOC removal efficiency. The successive oxidation of both pyrazole and DGA resulted in the production of formic acid, acetic acid, oxalic acid, nitrate ions and ammonium ions. Actual semiconductor industrial wastewater containing the same principal components as the lab-prepared water along with co-contaminants was treated with the three AOPs and the presence of co-contaminants lowered the removal rate constants of pyrazole and DGA for the Fenton and UV/H2O2 processes but increased those in the UV/Fenton process. Acute and chronic toxicity tests employing ceriodaphnia dubia indicated the wastewater after AOPs treatment showed no toxicity. © 2021 Elsevier B.V.