biodegradability improvement of olive oil mill wastewater by acid cracking and coagulation processes

background: olive oil wastewater  contains chemical contents and organic materials that are resistant to biodegradation.  the existence of phenolic inhibitor compounds, toxicity to microorganisms in wastewater treatment units, unpleasant odor, high biochemical oxygen demand (bod) and chemical oxygen demand (cod), high suspended solids, and compounds resistant to biodegradation in such wastewater are potential threats for surface and underground water resources. this study aimed to evaluate the efficiency of coagulation and acid cracking processes in olive oil wastewater treatment to reduce the pollution load and improve the biological degradability. methods: using a batch reactor, this study was conducted in laboratory scale on real wastewater. coagulation process was performed with alum and ferric chloride coagulants.  the wastewater from the best coagulant was treated by the acid cracking process using sulfuric acid. the removal of cod, total suspended solids (tss), and total phenolic compounds was investigated. findings: the results showed that the highest removal efficiency of pollutants was achieved in an optimum ph of 6 and a dose of 300 mg/l of ferric chloride. under these conditions, 91.2%, 89.7%, and 98.9% of  cod, tss, and phenolic compounds were removed.  in addition, ferric chloride was more efficient than alum. in optimum conditions, acid cracking process on the effluent from the coagulation process removed 18.6% of cod and 52.6% of total phenolic compounds.  bod/cod ratio  increased from 0.14 to 0.68 after the compound process. conclusion: these processes can be effective and economical methods to reduce pollution  in olive oil wastewater.