Photocatalytic oxidation of phenolic compounds in wastewater from oil shale treatment

Abstract

Experimental research into the photooxidation of aqueous solutions and wastewaters containing phenolic compounds was undertaken. Titanium dioxide under near-UV irradiation was selected as a photocatalyst. Phenol, p-cresol, resorcinol and 5-methylresorcinol (5-MR) were chosen as model compounds for the experiments with synthetic phenolic solutions. The photooxidative treatment of phenolic solutions was found to be more effective in acidic and strongly alkaline media. No difference was found between shortwave and near-UV irradiation photooxidation abilities. Methylated phenolic substitutes (p-cresol, 5-MR) yield better to photooxidation than non-methylated compounds. The higher the irradiation intensity the lower the photooxidation efficiency. The results obtained from the experiments with model compounds were compared with the results of photooxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia. Being heavily polluted, the wastewater yields better to photooxidation when slightly diluted with potable water in a 3:1 ratio. Anatase, immobilised onto the surface of buoyant hollow glass microspheres, was less effective than when suspended in a slurry. The photooxidatively pre-treated wastewater showed better biodegradability and lower toxicity to bacteria than untreated wastewater.