Olive mill wastewater: A potential source of natural dyes for textile dyeing
Highlights
► The olive mill wastewater (OMW) causes a serious ecological problem. ► OMW contains a valuable source of abundant natural colouring substances. ► OMW was used to dye woollen fibers at different dyeing conditions. ► The obtained shades were darker with generally good fastnesses. ► Mordanting improved generally light fastness.
Introduction
Olive oil is one of the oldest natural ingredients in the world. Its history goes back almost 8000 years to when the first trees (Fig. 1) were cultivated in the Syrian/Iranian region of the Middle East (Arvanitoyannis et al., 2007). Then, olives continued to move westward into Turkey, Greece, Egypt, Italy, France, Spain, Portugal, Algeria, Tunisia and Morocco. So far, olive oil industries have gained fundamental economic importance for many Mediterranean countries. The annual worldwide production of olive oil is estimated at ca. 1750 million metric tonnes with Spain, Italy, Greece, Tunisia and Portugal being the major producers (Arvanitoyannis et al., 2007).
During olive oil extraction, the manufactures produce two effluents, residual solids (husk) and large quantities of liquid effluents which are called olive oil wastewaters (OMW). For the second effluent, it is estimated that around 30 million m3 of OMW are generated annually in the Mediterranean area during the seasonal extraction of olive oil (Tezcan Ün et al., 2008, Adhoum and Monser, 2004).
Olive mill wastewater (OMW) is a dark-coloured liquid containing many dissolved and suspended substances. The solid content mainly comes from olive fruit residues such as olive pulp, husk, and some lignin derivatives that are not easily biodegraded. Table 1 summarizes some literature data concerning the constituents of olive oil wastewater (Lopez and Ramos-Cormenzana, 1996).
Wastewater from olive oil production is characterized by Tezcan Ün et al. (2008), Aragon (2000) and Panizza and Cerisola (2006):
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pH between 3 and 5.9 (slightly acid).
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Very high chemical oxygen demand COD (in the range of 40–200 g L−1), biological oxygen demand BOD (12–60 g L−1), total solids content (40–150 g L−1).
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High content of polyphenols, up to 80 g L−1.
Due to the high organic and polyphenols content of olive mill wastewater OMW, its direct disposal may pollute both land and aquatic environments. So, several methods have been proposed for OMW depollution, such as physico-chemical treatments like ultrafiltration, coagulation, evaporation, neutralisation, oxidation by O3, O3/H2O2 and Fenton reagent. But due to their high cost, few of these methods have ever been applied on an industrial scale (El Hajjouji et al., 2007, Fountoulakis et al., 2002). Biological methods, based on combinations of anaerobic and aerobic processes, have also been investigated (Borja et al., 1993, Tsonis, 1988). However, high phenols in the OMW have limited the effectiveness of these methods, due to their antibacterial activity (Fountoulakis et al., 2002). Nowadays, the most frequently used method is storage in evaporation ponds (Fig. 2) (Martinez Nieto et al., 1994, Fiestas and Borja, 1992). These wastewaters can be exploited in agriculture as soil biofertilizers (Mekki et al., 2007) or for building materials production (De la Casa et al., 2009). However, supplementary studies are required to evaluate their effect on the soil properties as well as on the underground water resource quality.
On the other hand, in recent years, there has been a growing tendency towards the use of natural dyes in textile coloration because of the increasing awareness of environment, ecology, pollution control and sustainability. However, this use in dyeing industry has remained timid due to the low availability and the high costs of natural dyes. Indeed, their use is mainly restricted to niche products for special markets such as the manufacturing of upmarket products and the textiles ecofriendly. Thus, considerable research works have been undertaken around the world to discover new sources of natural colouring agents and especially those with lower costs in order to make these textile products as popular as possible (Kamel et al., 2005, Montazer and Parvinzadeh, 2007, Bechtold et al., 2007a, Bechtold et al., 2007b, Shanker and Vankar, 2007, Vankar et al., 2008a, Vankar et al., 2008b, Vankar et al., 2009b, Vankar and Shanker, 2009a, Vankar et al., 2009b, Ali and El-Mohamedy, 2011). Although, OMW is an effluent presenting a serious ecological problem in Mediterranean countries, it contains a valuable potential of abundant natural colouring substances which are renewable, available with large quantities and free costs. Our preliminary experiments showed that this natural dye can be easily exploited in the dyeing of textile materials.
The present study focuses on the valorization of OMW extract in dyeing and fastness properties of wool fibres. The effects of some experimental conditions (dye bath pH, dye bath temperature, dyeing time and salt addition) on the dyeability of wool were investigated. Comparison between dyeing with and without mordants was made. The colour in all cases was evaluated by means of colour yield (K/S) as well as the CIELab coordinates and the corresponding fastness properties were also determined.
Section snippets
Materials and chemicals used
Prescoured wool fabric (Plain weave and weight, 118 g m−2) was procured commercially. Alum (KAl(SO4)2·12H2O, Fluka, Germany), potassium dichromate (K2CrO7, Fluka, Germany), ferrous sulphate hydrate (FeSO4·7H2O, Riedel-de-Haen, Germany), copper sulphate hydrate (CuSO4·5H2O, Fluka, Germany), stannous chloride (SnCl2, Aldrich, France) and sodium chloride (NaCl, Chimi-pharma, Tunisia) were laboratory reagents grade and were used without further purification. Hexane employed (Sigma–Aldrich, France)
Absorbance of the OMW aqueous fraction
The aqueous fraction of OMW is characterized by colour ranging from dark brown to black. This colour is chemically related mainly to polymers of low molecular weight phenolic compounds and tannins polymerization (Kallel et al., 2009, Yesilada et al., 1994, Hamdi and Garcia, 1993, Gonzalez et al., 1990). Phenolic compounds, generically, include great many organic substances that have the common characteristic of possessing an aromatic ring with one or more substituent hydroxyl group and a
Conclusion
This research reveals that olive mill wastewater (OMW) which is an effluent generated by the olive oil extracted industry causing a serious ecological problem in the Mediterranean countries, could be successfully exploited as dye bath for dyeing wool fabrics. The colour yield was generally high and the obtained shades were brown dark.
The study of the effects of different factors on dyeability of wool by OMW extract showed that the pH and the temperature of dye bath as well as the dyeing time
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