Developing a combined drying method to obtain high quality 2-phase olive oil pomace

The differences in olive oil production methods result in varied wastes in terms of property and quantity. Olive mill waste water and olive pomace possessing 35-40 % moisture come out in 3-phase system while only olive pomace possessing 60-70 % moisture comes out in 2-phase system. The quantity and pollution degree of waste water coming out in 3-phase system are considerably high compared to 2-phase system. Since recycling of 2-phase olive pomace containing also olive mill waste water, which is highly harmful for environment and is generally discharged to nature without any treatment, is considerably important by processing. In this study, the minimum quality loss of 2-phase olive pomace during drying and the system's energy efficiency is targeted with the use of the drum and tray dryer gradually. Pre-drying of 2-phase olive pomace was carried out by parametric drying at drum dryer supplying continuous mass production with a short drying time and obtaining high amount of dried sample. Vapor pressure and valse rotational speed were selected as the independent variables of drum dryer. For each vapor pressure value (1, 2, 3, 3.5 and 4 bar), drying of 2-phase olive pomace was performed at different valse rotational speeds (0.5, 1, 2, 3, 4.5 and 6 rpm). Drum dryer conditions were optimized with desirability function approach by targeting the moisture content range as 30-50 %, minimum peroxide value and maximum specific moisture extraction rate (SMER). The optimum drum dryer conditions were determined as 3.27 bar for vapor pressure and 6 rpm for valse rotational speed for pre-drying of 2-phase olive pomace. Moreover, the effects of vapor pressure and valse rotational speed on the physical and chemical properties of pre-dried 2-phase olive pomace (water activity, titratable acidity, pH, free fatty acid and specific absorption value at UV light (K232, K270, ∆E) and the system's energy efficiency (in terms of the moisture extraction rate (MER) and specific energy consumption (SEC)) were examined. After determination of the optimum drum dryer conditions, the effect of tray dryer's process conditions in terms of drying temperature (70-90°C), air velocity (0.5-1.8 m/s) and thickness of product (0.5-1.5) were investigated based on classical experimental design. The process parameters tray dryer were optimized considering of minimum drying time (min), minimum quality loss of olive pomace, maximum system energy efficiency. The optimum tray dryer conditions were 85.2 °C of drying temperature, 1.72 m/s of air velocity and 0.5 cm of product thickness as specified by using the Design Expert packaged software. Water activity, titratable acidity, pH, free fatty acid and specific absorption value at UV light (K232, K270, ∆E)) and the system's moisture extraction rate (MER) and specific energy consumption (SEC) were also examined which are not used in the optimization study but are very important for dried olive pomace quality. For the optimum conditions of tray dryer 3 independent variables were determined. Among the three of them, at each time two were changed. As a result of these drying experiments, the physical and chemical properties of the dried olive pomace and the performance of the drying system were compared. The experiments were also carried out to investigate the effect of drying area on the drying of 2-phase olive pomace. The physical and chemical properties of obtained olive pomace dried and system's energy efficiency were compared with each other. The effect of the addition of the mixing step at different processing times (15, 30, 45, 60, 75 min) was determined at the optimum tray dryer conditions. In the consequence of these drying experiments, the physical and chemical properties of dried olive pomace and the system performances were compared within the experimental design and with the results obtained from the optimum tray dryer's experiments. The drum and tray driers were operated consecutively as batch system at drying experiments. In other experiments the drum and tray dryer were used directly. As a result of these experiments, the physical and chemical properties of obtained olive pomace dried and system's energy efficiency were compared. As a result of the experiments where pre-dried 2-phase olive pomace at drum dryer was fed to the tray dryer directly, the quality of the dried olive pomace and system's energy efficiencies were improved. Thus, this method is useful and efficient for drying of 2-phase olive pomace. To detect the errors and uncertainties of tray dryer system, a detailed uncertainty analysis was performed. The drying characteristics of olive pomace and the drying behaviors were determined at all the drying experiments of tray dryer under different conditions. Logarithmic model which is determined the best semi-theoretical thin layer model in 11 empirical model by statistical analysis described the drying behavior of olive pomace at tray dryer experiments. Furthermore, the effect of tray dryer independent variables on drying rate, effective diffusivity and activation energy were examined. It was found that zero order kinetic model represented olive pomace's behavior of peroxide formation depending on statistical analysis. In addition, the effect of the independent variables of tray drier on reaction rate constant and activation energy of peroxide formation were determined.