OXIDATIVE PURIFICATION OF WASTEWATERS CONTAINING PHENOLIC-COMPOUNDS FROM OIL-SHALE TREATMENT

Experimental research into the oxidative purification of wastewaters p roduced from the thermal treatment of oil shale in Estonia was underta ken. The main toxic compounds of that wastewater were phenolic compoun ds, such as phenol, p-cresol and 5-methylresorcinol (5-MR). Ozone and hydrogen peroxide were selected as oxidants and a literature review fo r both is presented. The optimum pH range for the ozonation of 5-MR so lutions and of a wastewater were determined, as well as the specific o zone consumption. It was shown that under conditions of competitive re actions the volatile phenols decompose faster than the non-volatile on es. The treatment of phenolic solutions with hydrogen peroxide, in the presence of ferrous sulphate (Fenton's reagent), was found to be opti mal 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 comp ounds the lower the specific oxidant consumption. The reactivity of th e 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 toxi city stabilizes after the complete decomposition of the phenolic compo unds.