## 1 Introduction  
Olive cultivation and olive oil extraction constitute a major cultural and economic activity in the Mediterranean basin. Olive groves occupy about 10 million hectares of land area in the Mediterranean countries [1], where around 95% of the world's olive oil production is concentrated [2]. Presently, the largest area under olive groves in North Africa is located in Morocco, with over 1.2 million hectares under olive groves and a marked growth trend [1]. In fact, the surface under olive groves in Morocco has increased by over 60% in the last 25 years, which constitutes one of the largest increasing ratios in the world. Nowadays, the olive tree already represents the first fruit-bearing species under cultivation in Morocco, with about 65% of the national arboreal surface [3]. In terms of olive oil production, Morocco is the world's fourth largest producer with roughly 150,000 tonnes on average in the last ten years [2]. In addition, with an average production of approximately 125,000 tonnes in the last ten years, Morocco ranks second only after Spain in the production of table olives [2]. Olive trees grow in a large part of the Moroccan territory, except in the coastal areas and desert regions. As shown in the map presented in Figure 1, the most important regions for olive production are Fes-Meknes, Marrakech-Safi, Tanger-Tetouan-Al Hoceima, and Oriental [4; 5]. According to the recent statistics of the Moroccan Ministry of Agriculture, the three first regions account for about two thirds of the national olive production [3]. The olive oil industry in Morocco consists of about 11,000 traditional olive processing units (locally known as _masras_) with a capacity of just under 270,000 tonnes/year, 948 modern and semi-modern crushing units with a capacity of 1,803,000 tonnes/year, and nearly 75 olive canaries with a total capacity of 203,000 tonnes/year [4]. These olive processing units are mainly concentrated in the regions of Fes-Meknes (35.2%), Beni Mellal-Khenifra (17.3%), and Marrakech-Safi (11%). Moreover, beyond all these macroeconomics figures, which highlight the substantial economic significance of the olive prove in Morocco, it is noteworthy that this sector is an important driver for the development of rural areas, generating more than 380,000 permanent jobs, 20% of which are currently held by women [6]. In the olive oil industry, different methods are available to convert the olive fruit into virgin olive oil: a three-phase extraction process, a two-phase extraction process (continuous extraction), and a traditional press process (discontinuous) [7]. In Europe, the continuous two-phase extraction process is most widely used, mainly because of its  
Figure 1: Main olive-growing regions in Morocco (adapted on the basis of data from the Moroccan Ministry of Agriculture, Fisheries, Rural Development, Water and Forests [3]). reduced water consumption. Two-phase decanters are used in this oil extraction process, where olive pomace is massively obtained as the main by-product--a thick sludge made up of olive pulp and crushed pits [8]. However, the most commonly used process for olive oil production in North African countries is the three-phase extraction process. Three-phase centrifugal decanters allow for the separation of olive oil from three streams: two by-products--olive cake, a semisolid sludge composed of solid remains from the olives, and waste water from washing and processing of the olives [9]. The three-phase system typically produces about 20% olive oil, 30% olive cake, and 50% olive mill waste water [10], thus the weight of waste by-products is up to four times higher than that of olive oil. In the last ten years, a combination of the two-phase and the three-phase olive oil extraction processes is becoming increasingly more used in North African countries (Figure 2). In Morocco, the combined extraction system was introduced in high-capacity olive mills (\(>\)100 tonnes/day), where an additional extraction unit can lead to additional revenues [7].