Olive mill wastewater integrated purification through pre-treatments using coagulants and biological methods: Experimental, modelling and scale-up

In the Mediterranean countries, olive oil production is considered as an important economic activity among agro-industrial production, at the same time, discharge of Olive Mill Wastewater (OMWW) is also a severe problem in these regions. In any industry involving water and wastewater treatment processes, optimization is important for the development of new or enhancement of existing ones regarding economical and efficiency attributes and the like. In this work, the optimization of coagulation and flocculation was performed focusing on the effect of different pH and coagulant dosage values. In particular, pH, turbidity, Chemical Oxygen Demand (COD), Total Organic Carbon (TOC) and phenols were evaluated for all the experiments to check the efficiency, considering that OMWW sample had an initial pH equal to 4.5. Optimization of pH efficiency was tested at three different levels of pH (4.5, 4.0 and 3.0), by maintaining a constant dosage of two coagulants - aluminum sulphate (Alum) and chitosan equal to 400 mg/L and 100 mg/L, respectively. Subsequently, the best performing pH level was chosen and maintained constant for the optimization study of the coagulant dosage, ranging from 400 to 1,200 mg/L of alum and 300-700 mg/L of chitosan, respectively. It was observed that 60 min of sedimentation was sufficient to achieve a 99% reduction of turbidity for both alum and chitosan. With 800 mg/L of alum, a reduction in TOC, COD and phenols of about 16.76%, 57.16% and 62.89% respectively was achieved. The clarified water was then submitted to biological oxidation treatment where alum was the most efficient coagulant among those considered. In this second step, a further decrease of 82.5%, 71.9% and 99.6% in COD, TOC and phenols levels respectively were achieved. For both steps a kinetic analysis was performed: coagulation and biological oxidation processes have been modelled by different pseudo-nth order models, identifying for each process step the most suitable one. Based on the obtained results, the application of the integrated pre-treatment process using coagulation and biological methods would lead to a reduction of costs and an increase in efficiency of the final subsequent treatment step. (C) 2019 Elsevier Ltd. All rights reserved.