Solar Dryer Application for Olive Oil Mill Wastes

Abstract

Global waste production has raised recently due to numerous agricultural and industrial activities. Among other actions devoted to waste reduction, revaluation seems to be the most advantageous one from an environmental and economic point of view. In the olive oil sector, by-product management (namely olive pomace, olive mill wastewater, and sludge residue) poses serious problems for companies, with the energy use of these wastes being a feasible option to solve these problems. Due to their high moisture content, drying constitutes the main stage for a possible bio-fuel conversion. This research work deals with the analysis of drying for the three main wastes from olive oil by using a prototype dryer. This equipment has different working regimes depending on the kind of convection (natural or forced for passive and active mode, respectively), the incidence of solar radiation on the product (indirect or mixed type) and the use of an additional system for energy supply (hybrid type). From the results, it could be said that all the wastes were suitable for solar drying. However, drying conditions were different for each case. Olive pomace and olive mill wastewater showed promising results for solar drying application in mixed active mode. Concerning sludge residue, its special physical structure could employ the use of turners for drying, in order to improve heat transfer to the product. Moreover, hybrid active mode enabled a considerable reduction in drying time, being an aspect to take into account for its use during low solar radiation or at night time.

Solar process heat in industrial systems – A global review

“…Yuan et al researched on solar dryers used in carpet drying, thus evaluated its thermal performance [95]. Montero et al researched on solar drying systems used in drying wastes from oliveoil mills [55]. Liu et al reviewed 5 types of solar drying systems used in drying herbal Chinese medicine [46].…”

Olive Mill Wastewater: From a Pollutant to Green Fuels, Agricultural Water Source and Bio-Fertilizer—Part 1. The Drying Kinetics

“…Doymaz et al have examined the drying of olive cake by cabinet air drying at a constant air velocity of 1.2 m/s for different sample thicknesses and temperatures ranging between 80 and 110 • C [21]. Celma et al [22] and Montero et al [23] have studied the solar drying of the OMSW generated by the two-phase extraction system. Both studies compared different heat transfer configurations, including solar energy (coupled with heat from electrical resistances), natural convection and forced convection.…”

“…Several studies [21][22][23][24][25][26][27][28] have examined the drying of olive mill wastes using different drying systems. The drying process is generally a complex phenomenon where convection and diffusion phenomena participate.…”

Pre-drying of 2-Phase Olive Pomace by Drum Dryer to Improve Processability

“…The higher the energy transferred from the drying system to the dried product, the higher the amount of moisture content removed in unit time. Montero et al [36,37] used a solar dying system to dry olive pomace. The use of solar radiation and resistors as additional heating units along Fig.…”