REMOVAL OF PHENOLIC COMPOUNDS FROM WASTE WATER BY CATALYTIC WET AIR OXIDATION

Abstract

Wastewater treatment has become a major social, technological, economical and political problem. Modern legislation in our country imposes environmental regulations and health quality standards. The nature of pollutants and their concentrations in industrial wastewater depend on their source. Biological treatment is highly effective for the removal of most •of the contaminants, especially carbonaceous in nature. Despite their success and cost effectiveness, biodegradation processes are inherently slow and can not be used for the removal of toxic materials. Wet air oxidation is a well-established technique of importance for wastewater treatment, particularly toxic and non-biodegradable carbonaceous waste. This involves the liquid phase oxidation of organics or oxidizable inorganic components at elevated temperatures (125-320°C) and pressures (0.5 — 20 MPa) using a gaseous source of oxygen (usually air). Phenol is a common toxic organic compound and is a priority pollutant because it is extremely toxic to aquatic life, even at concentration in the parts per billion range, and it imparts a strong, disagreeable odor. The study of the wet air oxidation of aqueous solutions of phenols with emphasis on the catalyst selection and its synthesis, kinetics and mechanism of wet air oxidation by performing various experiments has been successfully done. From the literature survey we have been able to select the type of catalysts that are needed to be explored further towards their activities for the wet air oxidation of phenolic waste. iv The prime objective of the present studies will be towards reducing the severity of the operating conditions of temperature and pressure of the reactor. The catalysts, thus selected were CuSO4, CuO-ZnO/A1203, fly ash, LaCoO3 and Cu-X. After comparing the activities of the catalysts, the best catalyst has been further studied for the effect of various other parameters, such as, pH of the solution, feed to catalyst ratio, reaction time and pressure. The screening of the catalytic activities of the catalysts proposed were carried out at atmospheric pressure as well as in high pressure reaction vessel. Air was used as the oxidizing agent. The phenol concentration in feed and product were estimated using a gas liquid chromatograph. The total organic content in the waste water was found out by measuring the COD. CuO-ZnO/A1203 catalyst was found to be the best among the catalysts studied in the present work. A maximum 22.6% phenol conversion was obtained at temperature as low as 90°C, pressure 1 atm for a phenolic waste water having concentration 10 g/1 (COD 24,000 mg/I) using 1 g/l catalyst after 2 h reaction time.