(393a) Integrated Sustainability Assessment: Exergy, Emergy, Life Cycle Assessment

The word sustainable is a controversial concept because it has been defined in different ways by many disciplines. However, as of the 1980s, the word is used to refer to an appropriate management of natural resources, in such a way as to allow future generations the access to adequate resources. This definition was articulated in the Brundtland Report (Brundtland commission, 1987). In the Bruntland Report, the idea that a sustainability analysis interrelating economic development and environment was developed. Later, at 2005 World Summit on Social Development, objectives of sustainable development were identified: economic development, social development and environmental protection, also known as the three pillars of sustainability (United Nations General Assembly, 2005). Nearly all governments have in principle committed themselves to sustainable development by integrating economic welfare, environmental quality, and social coherence (Böhringer, C.; Jochem, 2007). The preservation of the natural environment is a prerequisite for a well-functioning economy and social justice. Therefore, sustainable development means something more than a compromise between the natural environment and pursuit of economic growth (Reza, Sadiq and Hewage, 2014). It means a definition of development which recognizes that sustainability limits have a structural origin both (economic) and natural.

Different methodological tools for sustainability assessment have been observed. Some oriented only to environmental sustainability based not only on the environmental burden (generated in the Life Cycle Assesment production chain) but also on the use of direct and indirect resources provided by nature for its manufacture, ending in the conception of the final product, and the investment and economic return that provides social welfare (Emergy Analysis, EmA). Others that include process efficiency in terms of entropy generated (Exergy Analysis, ExA). All these methodologies converge to the same point: tools that provide to the decision-makers environmental, economic or social sustainability indicators for the formulation and implementation of public policies. Another meeting point of these analytical methods is that each one has exactly the same methodological limitations: joint production, commensuration, deliberation, boundaries system setting, and double counting. However, this methodological tools that account for sustainability indicators in environmental, economic and / or social dimensions, cannot provide an assessment under these three dimensions in a robust way by themselves. Since some of them develop indicators that others do not, it is necessary to implement them as a complement but not as interchangeable techniques, providing additional information for decision making.

In recent years, there has been an increasing tendency to "integrate" different accounting methods to have a more complete picture of impacts caused by the creation of a product or service provision, instead of depending on a method that generally has a single criterion perspective (Kharrazi et al., 2014). These indicators can be taken as individual or composite parameters; that is, synthetic aggregations of independent parameters, reflecting the stakeholders values or considerations (Arbault et al., 2014). Regardless of whether individual or composite indicators are taken, a sustainable process should present an energy and technical feasibility that generates economic gains for social welfare with an acceptable environmental burden, hence the need to make use of all tools for assessing this sustainability, not as exchangeable but as complementary. A holistic view of the supply and value chain sustainability is necessary to ensure adequate management through an integrated approachable to assess processes from two points of view: "user-side" and "donor-side". User-side analyzes final efficiency indicators of the process (environmental impacts per unit of product generated, or energy / exergy delivered per unit of energy /exergy inverted). Donor-side considers the work nature does to provide resources for the production of a good or service, and in turn, to assimilate the pollutant load released to the environment as an important component of sustainability assessment. Accounting of the economic return in relation to the investment made cannot be ignored; as well as the effects and welfare that project execution can bring to society (Arbault et al., 2014).

Detractors of this integration argue that it is a reductionist approach, which leads to an assessment of the three sustainability dimensions through non-correlated factors (Arbault et al., 2014; Kharrazi et al., 2014). Although a holistic approach may result in the loss of information about each individual dimension and the indicators that compose them, it is also true that creating a holistic system-level image of the interactions between dimensions is critical for quantifying sustainability. The challenge is then to build methodological tools that can be integrated quantitatively into three dimensions.

Research aim is to propose a sustainability assessment framework to obtain a unified performance metric (Integrated Sustainability Index, ISI) to assess Triple Bottom Line – TBL. To achieve this integration, Life Cycle Assessment (LCA) and Exergy Analysis (ExA) as User-side approach, and Emergy Accounting (EmA) as donor-side view are implemented, in spite of the fact that each method differs on its basis of analysis and solve common methodological limitations in a different way. Some of the main issues faced by both designers and decision makers are precision and uncertainty in the calculation of these integrated indexes. This research presents systematically the proposed methodology to achieve the desired clarity and transparency. Methodological calculations supporting can be found at (Cano, 2018; Cano Londoño, Velásquez and McIntyre, 2019a, 2019b). The proposed sustainability index presents a comprehensible hierarchic structure determined by support methodologies such as LCA, ExA, and EmA, which have regulatory and academic validity. The integration of social, environmental, and economic components in an index that also allows the subjective adjustment of externalities reducing the risk of subjectivity, overshadowing rigorous work, is a new approach to assessing sustainability in development projects