Low Cost Treatment Plant For Olive Mill Wastewater

AdminOliveOil · #1 April 10th, 2006, 05:18 PM

LOW COST TREATMENT PLANT FOR OLIVE MILL WASTEWATER

Almost all of the world’s olive oil production and consumption has been realized in Mediterranean countries and 75 % of this value belongs to EU countries. Turkey amongst these countries is the second biggest table olive producer and the fourth for olive oil production after Spain, Italy and Greece. About 10 % of olive trees in the world are in Turkey. Olive trees are grown in Aegean, Marmara, Mediterranean and South East Anatolia Regions in Turkey. Olive mill wastewater (OMWW) generated by olive oil production, has high polluting and ecotoxicological properties and a big environmental problem which the solution is urgently necessary. OMWW is the most important pollution source in Mediterranean countries because of its serious pollution risk for superficial and underground waters. Olive oil production has been increased sharply at the last 35 years. Olive oil production plants are generally small family companies and spread everywhere in olive areas. Therefore, OMWW is discharged directly to soil, small rivers, lakes or sea; and environmental impact has been gained importance at the last years.

The industry of olive oil production generates large amounts of OMWW which has high COD/BOD5 ratio, high suspended solids concentration and phytotoxic and ecotoxic phenolic compounds. OMWW is a serious pollution risk for superficial and underground waters because of its high COD (60-200 g/lt) and BOD (20-100 g/lt) values and the presence of phytotoxic and antibacterial polyphenols. The values of BOD5 (Biological Oxygen Demand for 5 days), COD (chemical oxygen demand) and SS (suspended solid) of olive mill waste water are higher than typical domestic water values as much as 200-400 fold.

During olive oil production, solid and liquid wastes such as pomace and OMWW are also produced. Pomace is evaluated economically, but OMWW is discharged directly to the environment. OMWW includes essential chemical compounds which are found in olive. But, it has high polluting potential due to its high BOD5, COD, SS, oil-grease and phenolic compounds content. Due to high organic content, OMWW rapidly consumes dissolved oxygen in water sources such as sea and rivers. Therefore, all macro or micro organisms living in water can not continue their lives without oxygen. The dark color of OMWW disturbs the bright appearance of water and prevents the sun light absorption for photosynthetically growing organisms such as water plants and algae. Oil content of OMWW also forms film layer on water surface and prevents oxygen transport from air to water. Due to acidic characteristic, high salt and phenolic content, OMWW is dangerous for both water and soil. Therefore, it can not be used for irrigation as it is. OMWW is ecotoxicological dangerous affecting all living organisms in water and soil.

In this new wastewater treatment process, olive mill wastewater is treated by physical, chemical and advanced oxidation treatment methods. Olive mill wastewater is firstly fed to an oil skimmer. In oil skimmer unit, oil is gained 80 %. After this step, OMWW is fed to coagulation unit. In coagulation unit, pH value of OMWW is increased to 11.0 – 13.0 by adding lime powder which is transferred by an elevator and pH is held between these values with automatic pH control system. From this unit, OMWW is taken to a combined system settling tank. In the combined system settling unit, both flocculation and sedimentation processes are proceeded together. In this unit, 100 ml/lt of the 1 % solution of ME 697 (a special powdered polymer which is developed by the owner of this project), is added to flocculate the dissolved and suspended solids. Formed flocks pass to settling part. While flocks are settling to the bottom of the tank by the gravity, at the top of the tank, the treated wastewater is discharged. This treated wastewater is filtered through a zeolite bed and fed to an oxidation tank. In oxidation tank, wastewater is oxidized by adding 10 % solution of sodium hypochlorite until the redox potential reaches to the values between 450 – 600 mV and aerating. After this step, treated wastewater is passed through a zeolite filter first and then a UV/ozone system. This can be done by sequence or by circulation. At last, treated wastewater is passed through an activated carbon filter for dechlorination of the possible residual chlorine. By using this wastewater treatment process, BOD5, COD, oil-grease, phenolic compounds and SS can be removed 95 – 100%. The sludge formed by chemical treatment is collected in a sludge tank and then passed from a filter press and formed cake sludge is removed. Sludge can be utilized as fertilizer, fuel, soil binder and for the production of antioxidants.

Treatment studies for olive mill wastewater are continuing all over the world. But there is not any treatment method for OMWW which is economic and provides the discharge standards yet. According to studies, OMWW has been treated at the rate of 75 - 80% until our new investigated treatment process. By using our wastewater treatment process, OMWW can be treated economically and BOD5, COD, oil-grease, phenolic compounds and SS can be removed 95 – 100%. The treated wastewater is appropriate to the sewer discharge standards declared at the Table 25 of Water Pollution Control Regulation based on Turkish Environmental Law No: 2872.

Olive oil mills are small and medium sized and spread on a wide area. Most of them are family based companies. Therefore, our new investigated method is especially suitable for small olive oil mills. At this our new investigated technology, investment cost for an olive oil mill which processes 20 tones.olive/day is about 20.000 € and operating cost changes between 4-6 €/m3 according to chemical analysis of OMWW.

Report courtesy of erdincikizoglu

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