A potential and cost-effective treatment method utilizing thermally activated bentonite was evaluated for the treatment of highly loaded real petroleum processing wastewater (COD = 4500 mg/L) in order to reduce its COD and improve the corrosion properties. A save discharging COD limit of the treated effluent (800 mg/L) is achieved by using 6 g/L of calcinated bentonite after reaching the steady state (1 h of shaking) at pH 5. The durability of bentonite is proved. The corrosion behavior of the treated wastewater was investigated for mild steel by using electrochemical and weight loss measurements. The results proved that the corrosion rate of the wastewater was slightly reduced after the treatment process. More improvement of the corrosion resistance was achieved by adding sodium hexa-meta-phosphate (SHMP) corrosion inhibitor to the treated water. Tri-methyl ammonium bromide (CTAB) biocide was also added before discharging into municipal networks. Display omitted •Bentonite is used for removing of hazardous organics from petroleum wastewater.•The activated bentonite was more effective than the non-activated of about 20%.•The treatment method is considered to be cost effective and reliable technology.•Durability of bentonite is proved during the treatment process.•Corrosion control of municipal pipelines is considered for treated wastewater.