Oxidative purification of wastewaters containing phenolic compounds from oil shale treatment

Abstract

Abstract Experimental research into the oxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia was undertaken. The main toxic compounds of that wastewater were phenolic compounds, such as phenol, p‐cresol and 5‐methylresorcinol (5‐MR). Ozone and hydrogen peroxide were selected as oxidants and a literature review for both is presented. The optimum pH range for the ozonation of 5‐MR solutions and of a wastewater were determined, as well as the specific ozone consumption. It was shown that under conditions of competitive reactions the volatile phenols decompose faster than the non‐volatile ones. The treatment of phenolic solutions with hydrogen peroxide, in the presence of ferrous sulphate (Fenton's reagent), was found to be optimal in the pH range close to neutral. The catalyst, ferrous sulphate, is important for the oxidation rate but does not influence the process efficiency. The higher the initial concentration of the phenolic compounds the lower the specific oxidant consumption. The reactivity of the volatile phenols with hydrogen peroxide was also higher than that of the non ‐volatile phenols. The toxicity of the treated wastewater to Daphnia Magna decreased with increasing applied oxidant dose. The toxicity stabilizes after the complete decomposition of the phenolic compounds.