Combined treatment of phenolic wastewater by wet air oxidation and activated sludge

Wet air oxidation (WAO) is employed in this work for treating high concentration chemical wastewater containing phenol and/or phenolic compounds. Experimental results indicate that over 90% removal of phenol or phenolic compounds can be efficiently achieved in the WAO process. Despite of the high treatment efficiency of the WAO process, the treated wastewater, however, still retains relatively high chemical oxygen demand (COD) concentration and does not meet the safe discharge standard. Hence further treatment of the WAO treated wastewater by an aerobic biological treatment using acclimatized activated sludge is necessary. It is found in the present studies that the combined process, if appropriately operated, is capable of drastically reducing the COD concentration of the high concentration chemical wastewater to meet the safe discharge requirement. The operating conditions of the combined process are investigated to determine their respective effects on the overall treatment efficiency. The experimental data also indicate that the oxidation reaction can be represented by a first order kinetics in terms of the component or COD concentration. For both single component and multicomponent wastewaters, the WAO process was found to have different activation energy for oxidation below and above 200°C, suggesting possibly different reaction mechanisms between these temperature ranges. The experimental results provided in the present work can provide significant and practical information for optimizing the combined treatment method.