# Information and Communication Technology Solutions for the Circular Economy
## 1 Introduction  
Today's dominant \"take, make and dispose\" economic development model poses significant threats to the sustainability of the economies and of the natural ecosystems, which are of vital importance for humanity as a whole [1]. Circular economy (CE) comes as an alternative to the linear economy model [2, 3] based on:  
1. Smarter product manufacturing, efficient use of energy, materials, and resources, eliminating waste and pollution, and minimizing the use of virgin and non-renewable resources. 2. Keeping products and their parts at their highest value for a longer time, providing them with as many \"lives\" as possible, and optimizing their use not only during their first lifecycle, but during subsequent lifecycles as well. 3. Useful application of materials which are considered as waste, by regenerating natural resources and restoring finite materials to be used again. Several authors summarize the main ideas of CE in various so-called \"R\" frameworks. 3R, 4R, 6R, or even 9R, are some of the most popular frameworks revolving around the CE [4]. CE principles 1, 2, and 3, mentioned above, are directly related to the \"reduce\", \"reuse\", and \"recycle\" concepts of the 3R framework respectively. All three concepts are interconnected. For example, reusing a product or converting a product's components into useful materials through recycling also leads to the reduced use of virgin materials. The 4R approach uses \"recover\" as the fourth \"R\" to stress the importance of the recovery of the energy embedded in waste (e.g., through incineration). The 6R framework complements the 4R approach with the \"redesign\" and \"remanufacture\" concepts. \"Redesign\" refers to next-generation products, designed to use materials, components or resources recovered from the prior product lifecycle. \"Remanufacture\" includes new processing of used products in order to, fully or for the most part, restore them to their original state, by reusing as many parts as possible without a negative impact on their functionality [5]. Lastly, the 9R model complements the 4R framework with the concepts of \"rethink\" (maximizing how much a product is used, through sharing), \"repair\" (maintaining and repairing defective products, so that they serve their original purpose), \"refurbish\" (restore an old product and bring it up to date), \"remanufacture\" (same as in the 6R model), and \"repurpose\" (utilizing a discarded product or its parts in a product that has a different purpose or type of use). All of the frameworks share a hierarchy, with their first \"R\" function (e.g., \"reduce\" in the 4R framework) being prioritized over the second \"R\" (e.g., \"reuse\" in the 4R framework), the second one over the third one, and so forth [6]. Close cooperation within and among different sectors of the society, encompassing governments, academics, non-governmental organizations, businesses and the general public, is of vital importance for supporting and implementing the concepts of each framework [2]. Other approaches for CE also exist, such as the popular \"Regenerate, Share, Optimize, Loop, Virtualize, and Exchange\" (ReSOLVE) Model [7]. However, further analysis of such approaches falls out of the scope of the present study. In this paper, we considered the 4R Framework, which is in line with the core of the Waste Framework Directive 2008/98/EC [8], as the most suitable for the investigation and classification of information and communication (ICT) solutions that are designed to act as enablers for the CE. According to the definition used by UNESCO, the term ICT refers to various technological elements and solutions, which are used for the creation, transmission, storage, sharing and exchange of information [9]. Some examples of the technologies encompassed by the term are: computers, smartphones, internet, emails, telephony, satellite communications, broadcasting solutions, storage devices, software, robotics, etc. [10]. The current literature review has three main objectives.