Specifications of Exhausted Olive Pomace as an Energy Source: A Statistical Approach

Abstract

The olive oil industry is a seasonal agricultural activity in countries having the climate of the Mediterranean basin. Ripe olive fruits are harvested for two main reasons. They can be processed to yield pitted or un-pitted table olives or pressed to generate olive oil. In all cases there are by-products that need to be managed in a proper way to avoid their negative impacts on the environment. According to previous statistics covering the 2014-2016 period, about 176,000 olive trees were planted in Jordan [1,2].The main reason for the growing interest in planting olive trees is to produce olive oil and table olives in sufficient amounts to cope with the needs of the growing population in Jordan and to improve the income of many families. For example, in 2014 the self-sufficiency ratios of preserved olives and olive oil were estimated to be 114.3 and 103.4 %, respectively [3]. Recent statistics indicate that the number of olive trees in Jordan was 11.848 million trees [1]. In 2015 and 2014 olive harvest seasons, 156,639 and 118,215 tons of olive fruits were used for oil production, respectively. For the 2015 harvest season, 62.32 % of the pressed fruits was a harvest of the northern region of Jordan, while those harvested from central and southern regions were 26.23 and 11.45 %, respectively. These percentages are in accord with the geographical distribution of the number of trees in these regions [4].There are four types of olive mills in Jordan. Based on their oil extraction method, the four types are: the traditional press mill, the two-phase mill, the two-and-half-phase mill, and the three-phase mill. The most common type is the three-phase olive mills [5].Currently, the olive oil production is handled by 128 olive mills with regional distribution of 70%, 22%, and 8% in northern, central, and southern regions of Jordan, respectively. An input output analysis of the olive mills used in Jordan was reported [5]. The quantity and quality of the produced liquid and solid by-products depend on the type of the olive mill used for olive oil extraction [5]. For example, the percentage of moisture content of the fresh solid residue was estimated to be 26.15-28.25,48.30-52.17, and 54.6158.99 % for traditional mills, three-phase mills, and two-phase mills, respectively [5]. Other characteristics of the raw olive mill solid residue such as the content of residual fatty material, mineral content (ash), polyphenols, total carbon, and the carbon/ nitrogen ratio were also found to depend on the type of the olive mill [5].The four types of olive mills also have different rates for generating the Abstract: Samples of exhausted olive pomace were prepared from six slurry and sun-dried agglomerated raw olive pomace samples via Soxhlet hexane extraction treatment. For the case of exhausted olive pomace, the replicates of the measured percentages of carbon, hydrogen, nitrogen, ash, calculated oxygen, and the values of the gross and net calorific values were subjected to a thorough statistical analysis method. The results of the statistical analysis were reported as 95% confidence interval of a population mean. The numerical results of the statistical analysis, on dry basis, are: 49.230 ± 0.817 %, 5.888 ± 0.148 %, 1.397 ± 0.199 %, 1.797 ± 0.176 %, 40.716 ± 0.486 %, 20.069 ± 0.635 MJ/Kg, and 18.709 ± 0.605 MJ/Kg for C, H, N, ash, O, gross calorific value and net calorific value, respectively. Comparison of these results with those of the precursor raw olive pomace indicated that the exhausted pomace is enriched with N and O containing compounds. A cost analysis regarding the use of olive pomace as a cheap substitute for the highly-priced kerosene and diesel in home heating resulted in a saving of 260 USD per ton of combusted exhausted olive pomace.