## 1 Introduction  
Nowadays, the cyclic economy spirit globally makes imperative the need for exploitation of biomass and biowaste to balance the impact of industrial activities on environmental pollution and public health. One of the biomass exploitation products is the biomass derived from activated carbon (AC). Since the age of the ancient Egyptians, biomass-derived activated carbon (AC) has been used to enhance land fertility, as fuel, or in medical applications. Activated carbon (AC) is also used in many advanced applications such as catalyst supports, electrode materials, air filters, and gas storage, and since 1800, as an adsorbent for wastewater treatment [1; 2; 3; 4]. The last one is of great importance because clean water supply scarcity is one of the major problems in our days [5]. As a result, the world requirements for activated carbon (AC) are expected to increase dramatically and to reach the amount of 5424.9 kilotons by the year 2021 [6]. The USA and China will be the two largest markets of AC. This high demand will cause a high increase in the cost of AC [7] and consequently a limitation of the applications of AC as an adsorbent. A promising and ecofriendly approach to handle this problem is the production of activated carbon derived from biomass or biowaste [8]. Various adsorbents have been developed and used to remove dyes and other organic compounds from water. Among them, activated carbon (AC) is one of the most wildly used. This is because it has a well-developed pore structure with a high specific pore surface area, large pore volume, low density, high chemical resistance, and high adsorption capacity for various organic compounds [9]. Spent coffee (SCF) is a biowaste, the main quantity of which, following the linear economy model, ends up in a landfill. According to a study for the city of Sydney, this amount is around 93% of an annual quantity of 3000 tonnes of waste coffee grounds. The turn to the circular economy model proposes the exploitation of this biowaste for energy and high added value material production [10]. One of the major interests of these materials is the activated carbon (AC) produced via pyrolysis of spent coffee (SCF) and used for hexavalent chromium (Cr(VI)) removal. Hexavalent chromium (Cr(VI)) is considered to be one of the most toxic heavy metals. According to the World Health Organization (WHO), the permissible level in the water is 0.05 ppm [11]. This toxic pollutant waste is derived from chemical and metallurgical industries. The wastewater from such industrial activities contains 0.5-270 ppm of Cr(VI). For such concentrations, water purification is of vital importance. Nowadays, several researchers are investigating one of the most popular, simple, and eco-friendly methods for water treatment. This method is the adsorption of Cr(VI) on activated carbon (AC) originated from biomass or biowaste pyrolysis process. Spent coffee (SCF) is one of such biosources [12; 13; 14]. Although many conventional processes exhibited promising results for hexavalent chromium (Cr(VI)) removal from wastewater (e.g., chemical precipitation, ion exchange, membrane filtration, electrochemical treatment, and adsorption) [15; 16; 17; 18], each one of these processes also exhibited limitations [11]. Our method is an ecofriendly method, is not a high-cost process because the precursor material is waste, and exhibits high adsorption potential to reduce Cr(VI) concentration close to values required by the legislation. The main aim of this work was to combine the benefits of spent coffee biowaste valorization and wastewater purification through Cr(VI) removal by adsorption in bio-activated carbon. This attempt was expected to be successful because of the micropore structure of the produced AC.