Olive oil extraction industry wastewater treatment by coagulation and Fenton’s process

Abstract

The treatment of olive mill wastewater is a problem that still does not have an effective solution. In order to minimize this problem, there has been an improvement in the olive oil production process, moving from three-phase processes in oil mills to two-phase processes, and integrating the later with the oil extraction industry with n-hexane. This improvement does not totally solve the olive mill wastewater problem on its own, it only releases the olive mills from the environmental burden and concentrates the problem in the oil extraction industry. In this study it was proposed a treatment of a real effluent from an olive oil extraction industry, using the Fenton’s process integrated with coagulation. Different coagulant loads were studied to achieve the best conditions for this process. For the Fenton’s process, the loads of iron and hydrogen peroxide were optimized. The main evaluation parameters present in this study were chemical oxygen demand (COD), biodegradability and toxicity. Regarding the toxicity of the treated effluent, tests were performed on Aliivibrio fischeri.The studied effluent has a dark color, with an organic load of about 50 g L−1 of COD and high toxicity, with 9% of biodegradability. Coagulation process was studied with a single addition of coagulant (80 mg L−1) leading to 12.5 % ​​COD removal, while the combination of 20 mg L−1 plus 20 mg L−1 allows a COD reduction of 15 %. With the best conditions for coagulation (double phased addition of a total of 40 g L−1 of coagulant) integrated with the Fenton reaction (4 g L−1 of hydrogen peroxide, 2 g L−1 of iron (II) at pH 3 with 60 min of reaction) was possible to achieve about 45 % of COD removal. This allowed to increase the biodegradability, to a ratio higher than 40 %, for further biological treatment application to definitively treat the effluent.