## 1 Introduction  
Waste generation at a global level is one of the challenges of our constantly growing society [1]. In particular, the sustainable management of biowaste, which mainly includes food and pruning organic wastes, implies a challenge due to their increasing production in recent decades, but also an opportunity to transform them into a resource, also avoiding impacts on the environment [2]. This waste stream, with a high potential to become an added-value resource, plays a key role in the path towards a more circular economy, as it can be used to obtain high-value organic fertilizers such as compost [3]. Compostias a method to treat and valorize organic waste is based on the aerobic decomposition of the organic matter contained in the waste, in order to obtain a final material (compost), with maturity, stability, and humification properties; with fertilizing capacity; and without pathogens. This allows its use in agriculture as a growing medium, as a substitute for chemical fertilizers, without posing hazards to human health or the environment [4,5]. Thus, the European Union, through Directive (EU) 2018/851, establishes the separate collection and treatment of municipal organic waste, which includes, among other materials, biodegradable organic waste from food and kitchen waste from households, restaurants, catering establishments, and retail premises. Furthermore, it stipulates that the preparation for re-use and recycling of municipal waste should be augmented to a minimum of 55% by weight by 2025, progressively increasing this amount up to 65% by weight by 2035 [6]. Thus, traditionally, large-scale municipal solid waste management has been based on landfilling [7] and management in centralized facilities, where the environmental costs associated with transport and the long distances over which waste is transported have made waste management a serious issue [8]. Moreover, this type of large-scale composting facilities requires large areas and contributes to increased greenhouse gas emissions [9]. However, in recent decades, new environmentally friendly management models have emerged as decentralized composting models, such as community competing [3,10,11]. Different studies on this type of decentralized composting model have been conducted around the world, particularly in universities, municipal markets, and groups of households [12, 13, 14, 15, 16]. In this regard, in 2019, the campus of the Public University of Navarre (UPNA) launched the CaMPuSTAJE program, which aims to manage the biowaste generated in campus canteens through a simple community composting facility. In addition, the CaMPuSTAJE program is an excellent example of how the institution can address its strategic interests in sustainable waste management and how educational programs can be created to raise environmental and circular economy awareness among future graduates. Thus, UPNA students and graduates are actively engaged in the daily management of the program, whose one of these main aims is to promote experiential learning and applied research in sustainability and the circular economy [12]. As in other examples of community composting, this alternative method can be possible if the composting process is properly followed, from the design and dimensioning of the decentralized composting sites, as well as the characteristics of the used materials and final composts, to the training of staff in charge [17]. However, community composting, despite being extensively used in many countries and having increasingly attracted attention in the recent years, has been very little assessed [18]. Furthermore, until now, community composting has been only conceived as a reproduction of experiences from other places, without an analysis of the real needs of each case, a technical criterion or social perspective when making decisions [17].