The textile dyeing and the essential oil extraction industries are among the most successful industries in the Mediterranean basin (Plan, 2002; Baser and Buchbauer, 2015). Although their fields of activity are not related, these two types of industries have in common, in addition to their geographical proximity, their considerable volume of colored water discharges. Indeed, the amount of water generated by dyeing one kilogram of fabric is about 60 L, depending on the dyeing process (Bhatt and Rani, 2013). This water, strongly colored, represents a real ecological disaster that pushes more and more "eco-conscious" consumers to boycott textile products containing synthetic dyes. The same is true for buyers of essential oils who are generally health conscious and who realize that the product they have purchased is obtained through a non-ecological process. Indeed, the hydrodistillation extraction of one milliliter of oil requires the consumption of 0.5 to 1 liter of water (Wu et al., 2015; Filly et al., 2016; Gharred et al., 2019). At the end of the extraction process, the colored residual water is totally discharged in the environment without appropriate color removal treatment.
In the face of this ecological awareness that characterizes the first half of the 21st century, scientific research has increasingly focused on the development of cleaner industrial processes. Thus, in the field of textile dyeing, researchers such as Ben Ticha et al. have conducted extensive works to replace synthetic dyes, environmentally toxic, with natural dyes while achieving excellent dyeing performance (Ben Ticha et al., 2016). Other researchers have concentrated their efforts on minimizing water consumption and even replacing it with a so-called green solvent: supercritical CO2 (Banchero, 2013). Bishr et al. (2018) have extracted a fraction enriched in active principals (γ−Pyrones) from Ammi visnaga using supercritical CO2 as an alternative solvent for methanol, ethanol or hydro-ethanol.
The idea behind this work is to reduce the environmental impact of the essential oil extraction process by two complementary ways of valorisation: textile fiber dyeing by the aqueous residue of the hydrodistillation rich in colored substances and highlight the biological potential of the aqueous extract.
Inula is a vegetal genus that belongs to the Asteraceae family. It includes a variety of about 100 species, and is widely distributed in the Mediterranean basin. Species of this genus have been reported in the literature as having ethnopharmacological applications, to treat a wide range of disorders, mainly respiratory, digestive, inflammatory, dermatological, cancer and microbial diseases (Seca et al., 2014) thanks to their secondary metabolites such as flavonoids, sesquiterpenes and essential oils… Inula graveolens (L.) Desf. (Synonym: Dittrichia graveolens L. Greuter) is an annual aromatic plant with a foul camphor odor, it blooms from June to August. It is a nitrophilic species, growing on cultivated land, abandoned fields, roadsides and rural areas. Its leaves are oval and pointed and its flowers have yellow petals. Several studies concerning D. graveolens from different geographic zones have been reported and revealed its important pharmacological effects. Indeed, the D. graveolens ethanolic and methanolic extracts from Iraq, Jordan, Tunisia or Turkey showed antioxidant (Al-Fartosy, 2011), antiproliferative (Abu-Dahab and Affifi, 2007), allelopathic, antifungal (Omezzine et al., 2011), cytotoxic and antibacterial (Topçu et al., 1993) activities respectively. Moreover, the D. graveolens essential oil thanks to its wide use in aromatherapy was developed on a commercial scale (Blanc et al, 2004) under the name "odorous Inula"; this essential oil is recognized for its powerful actions on the respiratory system: mucolytic, expectorant, anticatarrhal and antitussive action and it is also known as a regulator and cardiac tonic. The distillation of the essential oil generates a considerable quantity of colored water discharge and according to the literature, no study has demonstrated the importance of these residues in textile dyeing. We therefore chose to focus for the first time on the reuse in an environmentally friendly way of the aqueous residue from the hydrodistillation of Tunisian "Inula graveolens" as a dye bath and evaluated its biological potential.
In this study and first of all, a chemical characterization of the aqueous residue was evaluated. Secondly, the aqueous residue was valorized as a dye bath for the polyamide fabric, the dyeing process was optimized thanks to Minitab 18 software using the response surface methodology (RSM). The color strength parameter (K/S) and the fastness values were determined for the optimum dyeing conditions. Finally, the antioxidant, antibacterial, cytotoxic and anti-inflammatory activities were evaluated in order to estimate the biological potential of the hydrodistillation aqueous residue.