**5. Molecular distillation**

302 Olive Oil – Constituents, Quality, Health Properties and Bioconversions

the acidity of the oil to 2.36%. In another study, the FFA content of high acidic (31.6%)

Bioremediation, generally classified as *in situ* or *ex situ*, is the use of microorganism metabolism to remove pollutants. *In situ* bioremediation involves treating the contaminated material at the site, while *ex situ* involves the removal of the contaminated material to be treated elsewhere. Some examples of bioremediation technologies are phytoremediation, bioventing, bioleaching, landfarming, composting, bioaugmentation, rhizofiltration, and biostimulation (Shukla et al., 2010). Besides being cost effective, bioremediation can result in the complete mineralization of the pollutant, considered a permanent solution of the pollution problem. Furthermore, it is a non-invasive technique, leaving the ecosystem intact. Bioremediation can deal with lower concentrations of contaminants where cleanup by physical or chemical methods would not be feasible. Unfortunately, it presents some major drawbacks which still limit the application of these techniques, including long processing

times and less predictable results compared to conventional methods (Perelo, 2010).

known as the two-phase olive-mill waste (Morillo et al., 2009).

The disposal of OMW is predominantly carried out via land spreading or by means of evaporation ponds, although a wide number of chemical and biological decontamination and valorisation technologies have been reported. The two-phase centrifugation system, as an alternative ecological approach for olive oil production, drastically reduces the water consumption during the process. This system generates olive oil plus a semi-solid waste,

Ramos-Cormenzana et al. (1996) performed aerobic biodegradation on OMW by using bacterium *Bacillus pumilus* to reduce the phenol content. They reported 50% reduction in phenol content using *Bacillus pumilu*s. The detoxification of OMW following inoculation with *Azotobacter vinelandii* (strain A) was performed for two successive 5-day-period cycles in an aerobic, biowheel-type reactor, under non-sterile conditions by Ehaliotis et al. (1999). The authors indicated that the phytotoxicity of the processed product was reduced by over 90% at the end of both cycles. However, aerobic bacteria cannot generally biodegrade complex phenolic compounds which are responsible for the dark color of OMW. Fungi, compared to bacteria, are more effective at degrading both simple and complex phenolic compounds presenting in olive mill wastes. This is due to the presence of compounds analogous to lignin monomers, which are more easily degraded by wood-rotting fungi

Demirer et al. (2000) generated biogas containing about 77% methane by anaerobic bioconversion of OMW (57.5 L methane per liter of wastewater). Ammary (2005) treated OMW using a lab scale anaerobic sequencing batch reactor, achieving more than 80% COD removal at 3 d hydraulic retention time. Anaerobic bioconversion has some advantages compared to aerobic processes: (a) high organic load feeds are used, (b) low nutrient requirements are necessary, (c) small quantities of excess sludge are usually produced, and (d) a combustible biogas is generated. However, the nutrient imbalance of OMW, mainly due to its high C/N ratios, low pH and the presence of biostatic and inhibitory substances, cause a problem. Not quite clear Rephrase An additional problem of two-phase olive-mill waste is its high consistency making its transport, storage and handling difficult (Morillo et al., 2009).

degummed and dewaxed olive oil was reduced to 3.7%.

**4.3 Bioremediation** 

(Garća Garća et al., 2000).

Molecular distillation, also called short path distillation, has become an important alternative for separation of heat sensitive compounds or substances with very high boiling points. Molecular distillation is characterized by a short time exposure of the distilled liquid to elevated temperature and high vacuum, with a small distance between the evaporator and the condenser (Lutišan et al., 2002). The small distance between the evaporator and the condenser and a high vacuum in the distillation gap results in a specic mass transfer mechanism with evaporation outputs as high as 20–40 gm−2 s−1 (Cvengroš et al., 2000). Due to short residence time and low temperature, distillation of heat-sensitive materials is accomplished without thermal decomposition. Another advantage of the process is the absence of solvents. Therefore, molecular distillation is considered as a promising method in the separation, purication and concentration of natural products (Martins et al., 2006).

Vegetable oil deodorization process produces a distillate rich in high value components such as phytosterols, tocopherols, and fatty acids, depending on the oil or fat. Martins et al. (2006) separated FFAs from soybean oil deodorizer distillate to obtain a tocopherol concentrate, which contained only 6.4% of FFA and 18.3% of tocopherols (from a raw material containing 57.8% of FFA and 8.97% of tocopherols.) The specific processing conditions were an evaporator temperature of 160 °C and a feed ow rate of 10.4 gmin−1. Under these conditions, they achieved 96% FFA elimination and 81% tocopherol recovery.

Although molecular distillation is a promising separation and purification method, it is not commonly applied in the olive oil industry. One relevant application is the purification of the structured lipids enzymatically produced from olive oil and caprylic acid (Fomuso & Akoh, 2002). If the advantages and efficiency of the system are further considered, it may be used in the olive oil industry for deacidification and separation of nutraceuticals. The cost of the system and possible alterations in the structure of the oil during the process seem to be serious disadvantages. Therefore, optimization of each particular system is necessary for a successful industrialization.
