Evaluation of ozone for the removal of phenolic compounds in wastewater from the Merisol Plant (Sasolburg)

Abstract

Ozone was evaluated for the removal of phenolic compounds in wastewater from the Merisol Plant. Oxidation was conducted under both acidic (pH = 4.70) and basic (pH = 10.45) conditions. Phenol and acetic acid (as well as traces of formic, butyric and propionic acids) were identified as major components in the Merisol effluent. The results from the study have indicated that the phenol concentrations in the Merisol effluent were reduced from an average of 355 mg/L to below detectable levels within 60 min of oxidation period under both acidic and basic conditions. Furthermore, the effluent COD concentration was reduced from approximately 1200 mg/L to: 678 mg/L at 40 ppm O3; 590 mg/L at 80 ppm O3; and to 579 mg/L at 120 ppm O3 under acidic conditions. Under basic conditions, the effluent COD concentration was reduced to: 656 mg/L at 40 ppm O3; 510 mg/L at 80 ppm O3; and 397 mg/L at 120 ppm. These results were well below the required 1000 mg/L COD specification level. Moreover, the results also indicated that oxidation of the Merisol effluent sample under basic conditions yielded better results when compared to oxidation under the normal pH of the effluent (acidic).The degradation products of phenol ozone oxidation were identified as formic, butyric and propionic acids. These acids occurred in various proportions during the oxidation and were also removed during the process. In conclusion, ozone oxidation technology has proven to capably treat the Merisol effluent to the required specifications. This technology may be applied to increase the degree of compliance of the Merisol Plant and that of Sasol One with regard to the Department of Water Affairs and Forestry (DWAF) phenol specification under the discharge water licence conditions.