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A biological integrated process for purifying olive oil waste water

A pilot plant was developed for a combined biological process to purify waste waters that originated from industrial olive milling, giving a significant reduction in the level of pollutants with energy recovery in the form of methane and/or ethanol production using an integrated biological approach.
The yearly world olive oil production is estimated at around 1.5 to 1.7 million ton/year This results in large amounts of effluent (olive mill wastewater or OMW). Research was carried out within the olive oil sector in Italy, Greece and Portugal and covered olive oil extraction technologies, OMW production and OMW treatment technology. Analytical methods (physico chemical, microbiological and toxicological) were developed and used to characterize OMW. For ethanol fermentation, yeast strains able to degrade the sugars present in OMW, with a conversion efficiency near to theoretical values, were selected. However the concentration of sugars in OMW observed was too low and hence the production of ethanol by fermentation was of no practical or economic interest. In contrast, anaerobic treatment was promising. The results obtained with a 17 l laboratory reactor gave higher rates of production of methane and chemical oxygen demand (COD) removal than reported in the literature. This process, when transferred to pilot plant reactors gave good yields during the first phase of the experiment until a dramatic frost stopped the reactor running. However, the analytical results indicated that using undiluted OMW it was possible to get similar results in the pilot plant as achieved in the laboratory. Hence, the process could be transferred to full scale if the following conditions were fulfilled: in start-up, large amounts of inoculum must be introduced gradually into the digester in order to facilitate microbial colonization; the OMW must be filtered using a system with smaller pores; the plant must be installed in areas where the climatic conditions are favourable, avoiding the risk of frost.

Reported by

Università degli Studi di Milano
20133 Milano
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