This paper presents an upgrading treatment of composite wastewater from a textile plant. The composite wastewater flow was around 4000 CMD and the wastewater characteristics showed an average COD of 817 mg/l. After biological and chemical treatment,the average COD's were reduced to around 187 mg/l and 101 mg/l,respectively. If compared to the new performance COD discharge standard of 100 mg/l here in Taiwan,the performance of this treatment system is obviously inadquate to comply with the above standard. In order to meet the regulatory requirement, the emphases of this study were placed on improving the performace of activated sludge as well as on the replacement of chemical coagulation unit by Fenton process. As aresult, by increasing biological nutrient does such as N,P,and Fe sources as well as by increasing food-to-microorganism ratio from 0.32 to 1.05 kg COD/kg MLSS‧Day, the effluent COD can further drop from 187 to 150 mg/l. It was found that the initial COD of 204 mg/l contained in the biological effluent can be reduced to around 50 mg/l after one hour reaction time under the conditions of 200 mg/l of H2O2,60 mg/l of Fe+2, and pH=3. In comparison. it appeared that the Fenton process performs better then the chemical coagulation.
