The treatment of high-strength petroleum refinery effluent (PRE) with [BOD5]/[COD]0 = 0.14 was
investigated using combined Fenton–sequencing batch reactor (SBR). The effect of [H2O2]:[COD]0 molar
ratio on biodegradability enhancement was investigated. Fenton optimal conditions were:
[H2O2]:[COD]0 of 6, [H2O2]:[Fe0] of 10 and pH = 3.0 that could remove 76.5%, 45% and 96% of COD,
TOC and phenol and increased biodegradability ratio to 0.37. The pretreated PRE subjected to SBR for one
single cycle of 10 h. The results revealed the effectiveness of hybrid Fenton–SBR system in treating PRE
where the complete treatment of the PRE was attained by this system.