Nowadays, the treatment of mixed domestic–industrial wastewater has gained more attention, so, the main target of the study is to degrade the wastewater through a combination of primary, biological, and advanced oxidation processes. To enhance the treatment of the wastewater, the processes of coagulation, flocculation and sedimentation were applied before the biological treatment. The effect of the type and dose coagulants and effect of using polyacrylamide (PAM) as a coagulant aid were studied. The optimized conditions selected for the experiments were ferric chloride and alum. They showed a close treatment effectiveness since 400 mg/L was the best coagulant dose, and 10 mg/L was the best PAM dose. The chemical oxygen demand (COD), biological oxygen demand (BOD5 ), and total suspended solids (TSS) removal efficiencies were 58.8%, 55.9% and 67.5%, respectively at 10 mg/L PAM and 400 mg/L alum doses. When doses of ferric chloride and PAM were at 400 and 10 mg/L sequentially, the removal efficiency of COD, BOD5 and TSS were 61.8%, 59.7% and 71.1%, respectively. After the primary treatment, extended aeration was used for the biological wastewater treatment. The study aimed to evaluate the effect of hydraulic retention time (HRT) on the performance of the biological treatment via extended aeration. The removal rates at HRT of 24 h for COD, BOD5 , TSS and total Kjeldahl nitrogen (TKN) were 70.6%, 86.2%, 58% and 70.7%, respectively. Increasing the HRT more than 24 h exerted a slight improvement in the pollutant removal efficiency. After the biological treatment, COD, BOD5 , TSS and TKN in the effluent decreased, but the values did not meet the Egyptian standards. A Fenton process was provided in the treatment to ensure that the COD removal as stipulated by the regulations would be obtained in the final effluent. Different reaction conditions of Fenton treatment were examined, including H2 O2 concentration and H2 O2 /Fe2+ ratios. The maximum removal was achieved at H2 O2 / COD = 4.7. In addition, five different H2 O2 /Fe2+ molar ratios (20–160) were tested. COD removal percentage was 68.4% at the molar ratio of 160 and increased to 84.9% at the molar ratio of 40.