Life Cycle Assessment
In order to help decision makers correctly consider the comparative environmental impacts of virgin PP fibre, recycled PP fibres and steel reinforcing mesh in concrete footpaths, it is very important to carry out environmental impact assessment (EIA). The environmental impact assessment is a formal process used to predict the positive or negative environmental consequences of a project prior to making decisions (Achilleos et al. 2011; Carvalho et al. 2014). There are a variety of general and industry specific assessment methods, such as GMP-RAM (Jesus et al. 2006), INOVA Systems (Jesus-Hitzschky 2007), fuzzy logic EIA method (Afrinaldi and Zhang 2014; Peche and Rodriguez 2009). However, life cycle assessment (LCA) (Sandin et al. 2014) is the most comprehensive among the available tools and widely adopted and used in a wide variety of applications. For example, the LCA is widely used in building assessment (Gabel et al. 2004; Ingrao et al. 2014; Iribarren et al. 2015; Silvestre et al. 2014) and its implementation must adhere to standards ISO14040: 2006 (ISO14040 2006) and ISO14044: 2006 (ISO14044 2006).
Life cycle assessment is commonly used to identify and measure the impacts associated with all the stages of a product’s life from-cradle-to-grave (i.e., from raw material extraction and raw materials processing, to product manufacture, distribution, use, repair and maintenance, and ending with disposal or recycling). It considers all stages to evaluate the environmental burdens associated with a product, process, or activity by identifying and quantifying energy consumed, materials used and waste released to the environment (Sandin et al. 2014). The LCA methodology is generally considered the best environmental management tool for quantifying and comparing alternative eco-performances of products, as well as recycling and disposal systems (Lasvaux et al. 2014). The structure of LCA consists of four distinct phases: goal and scope definition, inventory analysis, impact assessment and interpretation (Dodbiba et al. 2007).
The goal of an LCA states the intended application, the reasons for carrying out the study, the intended audience, and where the results are going to be used. The scope should be sufficiently well defined to ensure that the breadth, depth and details of the study are compatible and sufficient to address the stated goal. It includes the following items: the product system to be studied; the functional unit; the system boundary; allocation procedures; impact categories and methodology of impact assessment, and subsequent interpretation to be used; data requirements; assumptions; limitations; initial data quality requirements; and format of the report required for the study.
Inventory analysis involves data collection and calculation procedures to quantify relevant inputs and outputs of a product system. Data for each unit process within the systems boundary can be classified under major headings, including energy inputs, raw material inputs, ancillary inputs, other physical inputs; products, co-products and waste; emissions to air, discharges to water and soil, and other environmental aspects. Following the data collection, calculation procedures, including validation of data collected, the relating of data to unit processes, and the relating of data to the reference flow of the functional unit, are needed to generate the results of the inventory of the defined system for each unit process and for the defined functional unit of the product system that is to be modelled.
The impact assessment phase of LCA aims at evaluating the significance of potential environmental impacts using the life cycle impact (LCI) results. In general, this process involves associating inventory data with specific environmental impact categories and category indicators, thereby attempting to understand these impacts. Interpretation is the phase of LCA in which the findings from the inventory analysis and the impact assessment are considered together. The interpretation phase should deliver results that are consistent with the defined goal and scope and which reach conclusions, explain limitations and provide recommendations (Viksne et al. 2004).
Perugini et al. (2005) studied the LCA for recycling of Italian household plastic packaging waste. Their study quantified the overall environmental performances of mechanical recycling of plastic containers in Italy and compared them with conventional options of landfilling or incineration, as well as comparing with other innovative processes of feedstock recycling (low-temperature fluidised bed pyrolysis, and high-pressure hydrogenation). Their results confirmed that recycling scenarios were always preferable to those of non-recycling. Arena et al. (2003) also studied the Italian system of collecting and mechanically recycling the post-consumer polyethylene (PE) and polyethylene terephthalate (PET) liquid containers. They found that the production of recycled PET can save between 29 and 45% of energy compared to virgin PET production, depending on whether the process wastes (mainly coming from sorting and reprocessing activities) were used for energy recovery. Moreover, 39-50% reductions in energy use were observed in the production of recycled PE compared to virgin PE.
Shen et al. (2010) assessed the environmental impact of PET bottle-to-fibre recycling. Four recycling cases, including mechanical recycling, semi-mechanical recycling, back-to-oligomer recycling and back-to-monomer recycling were analysed. The LCA results showed that recycled PET fibres offered important environmental benefits over virgin PET fibre, including energy use savings of 40-85%.