## 1 Introduction  
In this research, the solid by-products remaining after the distillation of lavender, which are still little studied in scientific literature, are taken into account as a potential and still underutilized source of bioactive compounds to be valorized. These solid wastes, sometimes called \"distilled straws of lavender\" are lignocellulosic-rich materials, which have been proposed as an interesting source to be converted into biofuel [1]. However, this biomass is still rich in bioactive compounds, mainly antioxidants, whose extraction could represent a useful first step towards its utilization as an economic resource still to be exploited. This recycling possibility has been evaluated inside a European research project called Finnover. Finnover (for \"Innovative strategies for the development of cross border green supply chains\"), is a cross-border Italy/France EU Interreg Alcotra project started in 2017 and finished in 2021 [2]. The aims of this research project were the innovation and the sustainable implementation of several agro-industrial processing chains in view of the green circular economy and the valorization of the biodiversity of the Alcotra territory. In particular, the management of waste deriving from agricultural and food processing is one of the main topics of the project, offering new perspectives to floriculture enterprises by recovering useful bioproducts from the waste produced during the distillation of essential oils from lavender and other aromatic species. The _Lavendula_ genus, which belongs to the Lamiaceae family and includes numerous varieties and hybrids, is one of the best-known essential oil crops in the world [3]. _Lavandula angustifolia_ Miller (syn. _L. vera_ or _L. officinalis_) is an evergreen and perennial flowering shrub and it represents, among aromatic plants, the most common cultivated species in the Mediterranean coasts [4]. Lavender has been widely used as herbal medicine for centuries in the traditional medicine. Particularly, lavender essential oil (LEO) is commonly used in pharmaceutical products, phytomedicine preparations, as well as in foods and cosmetics [5]. One of the main uses of LEO is in inhalation aromatherapy, due to its numerous sedative [6], anti-inflammatory [7], antidepressant [8], antiseptic [9], analgesic [10] and antispasmodic [11] healing properties. In the food industry, LEO is mainly employed as a natural antibacterial to preserve food products and extend their shelf life, and as a flavoring agent in several foodstuffs (i.e., beverages, sweets, candies and chewing gums) [12,13]. As concerns the extraction process, steam distillation has traditionally been used to recover the essential oil from lavender flowers. This extraction procedure is industrially the most frequently used method because its simplicity, low cost, and safety (no environmental impact) [14]. LEO is produced from raw plant materials (flowers, buds, stems and leaves) by steam distillation, but yields are low with only 2-10% volume/dry weight [1] with a large amount of by-products: liquid and solid secondary products. The liquid secondary products of the distillation process of essential oils are the distillation wastewaters namely hydrolats (or hydrosols or aromatic waters) and leachates. During steam distillation, volatile plant constituents are vaporized and then condensed on cooling to produce an immiscible mixture of an oil phase and an aqueous phase, named hydrolat. The hydrolat contains both traces of the essential oil (generally less than 1 g/L) and several water-soluble components with low molecular weight [15]. Leachates are aqueous mixtures too, containing water-soluble compounds with high molecular weight, which are extracted from the plant matrix by heating but do not undergo the distillation process (Figure 1). Furthermore, after obtaining the essential oil (LEO) there remains a solid waste represented by the residues of the flowers and leaves, which does not yet have any real industrial value.