Characterization of Wet Olive Pomace Waste as Bio Based Resource for Leather Tanning.

M Mercè Solé,Anna Bacardit,Laia Pons,Carmen Gaidau,Mireia Conde

doi:10.3390/ma14195790

Abstract

Olive mill wastes represent an important environmental problem. Their high phenol, lipid, and organic acid concentrations turn them into phytotoxic materials. Specifically, wet olive pomace (WOP) is the waste generated in the two-phase continuous extraction process. WOP is a paste with around 60% water. The total volume of WOP generated is around 0.25 L/kg of olives processed. Its current waste management practices result in environmental problems as soil contamination, underground seepage, water-bodies pollution, and foul odor emissions. Some valorization alternatives include composting, biological treatments, direct combustion for energy production, or direct land application. The leather industry is making great efforts to apply cleaner processes while substituting chemical products for natural products. In this way, different alternatives are being studied, such as the use of zeolites, triazine derivatives, grape seed extract, olive leaf extract, etc. In this work, the use of wet olive pomace is presented as a possible alternative to conventional vegetable tannins (mimosa, quebracho, chestnut, etc.). Although different projects and studies have been developed for the valorization of olive mill wastes, there is completely a new approach to the WOP application for tanning purposes. This study shows that WOP has a significant number of polyphenolic substances, so it has a great potential to be used as a tanning agent. Specifically, this study has been able to determine that, of the polyphenols present in WOP, 39.6% correspond to tannins that are capable of tanning the skin. Additionally, it contains 14.3% non-tannins, that is, molecules that by themselves do not have the capacity to tan the leather but promote the tanning mechanism and improve the properties of the tanned leather.

Highlights

On the one hand, the leather industry transforms rawhide into leather through mechanical and chemical processes
This study shows that wet olive pomace (WOP) has a significant number of polyphenolic substances, so it has a great potential to be used as a tanning agent
When a ton of raw hides is converted into approximately 250 kg of leather, around 500 kg of chemicals are added during the tanning process; and between 20–50 m3 of wastewater are generated, between 600–900 kg of solid waste and 40 kg of emissions in the form of volatile compounds [1]

Summary

Introduction

The leather industry transforms rawhide into leather through mechanical and chemical processes. When a ton of raw hides is converted into approximately 250 kg of leather, around 500 kg of chemicals are added during the tanning process; and between 20–50 m3 of wastewater are generated, between 600–900 kg of solid waste and 40 kg of emissions in the form of volatile compounds [1] In this way, the leather industry is making great efforts to apply cleaner processes while substituting chemical products for natural products and searching for alternatives to chrome tanning such as organic tanning consisting of phenolic synthetic products, aluminum salts, as well as vegetable tanning [2,3,4,5]. The most acceptable reaction is binding to the CO-NH bond of the protein through the phenolic hydroxyl group of the vegetable tannin, among other secondary reactions [7,8]

Objectives

Methods

Results