The chemical properties of the wastewater of 17 olive mills in the area between Al-Dafniyah into Qaraboli in the west of Libya were studied and chemical coagulants such as alum, ferric chloride, chemical oxidation, and biochar were used to remove the organic load and phenolic compounds from this water. The results showed that the wastewater of the olive mill is highly acidic with an average pH of 5.15 and its high content of solids reached 192 g/L, while the average of dissolved solids was 63.5 g/L and the organic solids were about 90% of the total solids and the average of chemical oxygen demand is 104.9 g O2/L, and the concentration of phenolic compounds is high and it was 1.86 g /L. In addition, the results showed that the usage of Ferric chloride as a coagulant gave higher removal percentage of phenolic compounds, dissolved solids, and chemical oxygen demand in comparison with Alum in the pH range of 6-9. The removal percentage was higher in alkaline pH, especially for phenolic compounds. Moreover, increasing the amount of the coagulant from 2 to 16 g/L enhanced the removal of phenolic compounds and chemical oxygen demand, while the removal efficiency of dissolved solids was weak, which required the use of chemical oxidation and adsorption on biochar to improve the efficiency of the removal. Although sequential treatments by coagulants and chemical oxidation by Fenton solution or biochar improved the percentage of removal in biochar treatments compared to chemical oxidation, the concentration of pollutants is still high for disposal, especially phenolic compounds. As a result of that, these methods need more studies to improve them. Langmuir and Freundlich’s models gave a good describing the adsorption of phenolic compounds on the surface of biochar. However, the adsorption capacity is low compared to the scientific literature, because this study uses raw olive mill wastewater with a high organic load, which causes competition between these substances on the adsorption sites or inhibits adsorption by depositing them on the surface of the biochar.