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  Background: Olive oil extraction in the world is considered an important economic activity . Environmental impacts of olive oil wastewater is related to the chemical contents and organic materials load that are resistant to biodegradation. Olive wastewater due to phenolic compounds, inhibitors, toxicity to microorganisms in municipal wastewater treatment units, unpleasant odor, high COD, high BOD, high suspended solids, high resistant compounds to biodegradation, the threat potential to surface and underground water resources is to be considered and paid attention to. So far, several studies in olive oil mill wastewater treatment are carried out. This study aimed to determine efficiency of coagulation process in olive oil wastewater treatment to reduce pollution load and improve the biological degradability.

  Methods: This study was conducted in laboratory scale and Batch reactor on the real wastewater. Coagulation process using alum and polyaluminum chloride (PAC) coagulants was done and the removal value of COD, TSS and total phenolic compounds was investigated.

  Results: The results demonstrated that the highest removal efficiency of pollutants in the optimum pH and dose of PAC achieved turned out to be 7 and 1 000 mg/L respectively. In these conditions , the removal values of COD, TSS and total phenolic compounds by PAC achieved were 88 .3, 90.2 and 9 9 . 2 %, respectively. Also analysis of the ratio of BOD/COD showed that after coagulation process, the value could increase from 0.14 up to 0. 5 8.

  Conclusion: This process can be regarded an effective and economical method in the reduction of pollution of this type of wastewater.