The continuous depletion of natural resources related to our lifestyle cannot be sustained indefinitely. Two major lines of action can be taken to overcome this challenge: the application of waste prevention policies and the shift from the classical linear Integrated Waste Management Systems (IWMSs) that focus solely on the treatment of Municipal Solid Waste (MSW) to circular IWMSs (CIWMSs) that combine waste and materials management, incentivizing the circularity of resources. The system analysis tools applied to design and assess the performance of linear IWMSs were reviewed in order to identify the weak spots of these methodologies, the difficulties of applying them to CIWMSs, and the topics that could benefit from further research and standardization. The findings of the literature review provided the basis to develop a methodological framework for the analysis of CIWMSs that relies on the expansion of the typical IWMS boundaries to include the upstream subsystems that reflect the transformation of resources and its interconnections with the waste management subsystems.

Introduction

Resources within planet Earth are finite by nature. Natural resources whose formation roots in other geologic periods, like mineral deposits, cannot be renewed in human timescales and thus their reservoirs are bound to eventually become depleted if their consumption continues (Prior et al., 2012; Shafiee and Topal, 2009). On the other hand, natural stocks subject to biological cycles (a population of trees for example) yield a sustainable flow of valuable goods and services (such as wood and CO2 removal from the atmosphere) on a continuous basis (Costanza and Daly, 1992). Nonetheless, since the early 1970s some renewable natural resources are being exploited faster than they can be renewed (Borucke et al., 2013). As a matter of fact, it would take 1.64 planets to regenerate in one year the natural resources consumed in 2016 (Global Footprint Network, 2016). This figure is expected to worsen because of the projected population increase and the improved acquisition levels of the emerging economies (Foley et al., 2011; Karak et al., 2012). If the consumption of raw materials rises, so does waste generation (Shahbazi et al., 2016). Around 1.3 billion tons of MSW are annually produced in cities all over the world (Hoornweg and Bhada-Tata, 2012), and a significant amount of the waste produced in low and lower-middle income countries is disposed of in open dumps (Hoornweg and Bhada-Tata, 2012) lacking measures to prevent safety and environmental hazards. Under the assumption that every ton of MSW generated in cities worldwide could be stored in 1 m3 of sanitary landfill (Li et al., 2013), a landfill volume equivalent to that of 347,000 Olympic swimming pools would be required every year. Accordingly, policies against landfills are mostly motivated by a lack of space, particularly in the highly populated areas of Europe and Asia, where landfills are more likely to interfere with other land uses like agriculture (Moh and Abd Manaf, 2014). In fact, waste valorization might help to overcome one of the most pressing global challenges: securing the food supply. Waste has been suggested as a plausible source to recover phosphorus (Reijnders, 2014; Tarayre et al., 2016; Withers et al., 2015), an essential nutrient to the metabolism of plants and by extension to agriculture, whose remaining accessible reserves could run out as soon as 50 years from now (Gilbert, 2009). Hence, as the principles of industrial ecology dictate, resources and waste management are key to meeting the future needs of society in a sustainable manner. Waste prevention activities or policies such as restricting planned obsolescence in electronic products and measures like minimizing product weight or design for disassembly (Li et al., 2015) will contribute to tackle these issues. A reduction in the consumption of natural resources and the amount of waste generated would also be accomplished if a shift to circular economic and production systems, mimicking the self-sustaining closed loop systems found in nature, such as the water cycle, was put into practice. A circular economy aims at transforming waste back into a resource, by reversing the dominant linear trend of extracting, processing, consuming or using and then disposing of raw materials, with the ultimate goal of preserving natural resources while maintaining the economic growth and minimizing the environmental impacts (Ghisellini et al., 2016; Lieder and Rashid, 2016).