Inventory analysis

In this phase, all the data collection and calculation of inputs and outputs is performed.

Qualitative and quantitative data for each unit process in the product system should be

collected by measuring, calculation or estimation. A process flow diagram, that includes

the processes and their relationships, should be developed. Data collected might be

classified as suggested in ISO 14044:

“- energy inputs, raw material inputs, ancillary inputs, other physical inputs,

- products, co-products and waste,

- releases to air, water and soil, and

- other environmental aspects”

The calculation includes the accounting of all the inputs and outputs of processes in the

flowchart. A software tool that provides a framework to organise the product system and

perform the calculations is typically used (e.g. Simapro (PRe Consultants, 2011)). The use

of commercial databases which have access to common products is a general practise in

LCA.

The results of an inventory analysis are the product and elementary flows involved in the

product system, normalised according to the functional unit. A product flow (economic

flow) is “products entering from or leaving to another product system” and an elementary

flow (natural flow) is “material or energy entering the system being studied that has been

drawn from the environment without previous human transformation, or material or energy

leaving the system being studied that is released into the environment without subsequent

human transformation” (ISO, 2006b).

2.2.4.2.1 Co-product handling

Co-product handling is required when a process produces more than one co-product. A

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system” (ISO, 2006a). Allocation is “partitioning the input or output flows of a process or a

product system between the products system under study and one or more other product

systems”.

Wastes are also outputs; however inputs and outputs should be allocated to co-products

only. Wastes in LCA are “substances or objects which the holder intends or is required to

dispose of” (ISO, 2006b). Econometrica et al. (2009) studied the indirect GHG missions

from the use of wastes, residues and by-products in the UK. They recognised that the

terms “waste”, “residues” and “by-products” normally do not have the same definition in

legislation and LCA. This can make the use of these terms complex and confusing. ISO

14044 provides a hierarchy regarding co-product handling which suggests that:

- Allocation should be avoided either by process division or system expansion.

- If allocation has to be performed, the inputs and outputs of the system should be

divided according to the physical relationships in which inputs and outputs change

according to changes in their functions.

- If no physical relationships can be defined, other relationships should be used (e.g.

economic value of products and co-products).

Reuse and recycling have special requirements, since these processes (and similar like:

composting, energy recovery, etc.) involve more than one product (ISO, 2006b). For

these, there are two cases for allocation:

- Closed-loop allocation is used where the properties of the recycled material are

the same as the virgin material. Allocation is not needed since the secondary

material production reduces the use of the virgin material.

- Open-loop allocation is used when the material is recycled or reused in other

product systems.

Allocation and system expansion are among the most debated issues in LCA

methodology (Weidema, 1993; Azapagic and Clift, 1999b; a; Ekvall and Finnveden, 2001;

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that there is no single method to solve the multiple output problem (Guinee et al., 2004;

Curran, 2007a; Kendall and Chang, 2009). Approaches that are used include:

- Main or primary product (or no allocation): the main product takes all the

environmental burden of the system.

- Economic allocation: the economic value ratio of the co-products is used to divide

the environmental burden among co-products.

- Mass allocation: the mass proportion of the co-products is used to divide the

environmental burden (a similar approach can be taken with volume).

- System expansion: the avoidance of allocation through the inclusion of avoided

products from other products systems in the studied system.

- Biological allocation: it has been argued that biological causality could be used in

biological product systems (Ayer et al., 2007; Schau and Fet, 2008). One example

is in milk based systems, allocation can be based on the energy required to

produce milk, maintenance, growing, pregnancy, etc.

Economic allocation and system expansion seem to be the methods that are used most

often; however, they both have advantages and disadvantages (Table 9). In studies

related to agricultural and food systems, economic allocation is normally the most used

co-product handling method (Ayer et al., 2007; Schau and Fet, 2008; Kendall and Chang,

2009), probably because it is a generally applicable method.

Table 9 Advantages and disadvantages of economic allocation and system expansion

Economic allocation System expansion

Advantages Generally applicable (Weidema,

1993; Guinee et al., 2004) Adequate to analyse changes in the product system, demand or

production volume (Ekvall and

Finnveden, 2001; Cederberg and Stadig, 2003)

Disadvantages Economic value varies with time

(Ayer et al., 2007; Feitz et al., 2007) Tariffs and subsidies make it imperfect (Feitz et al., 2007; Schau and Fet, 2008)

Does not represent the effect of decisions (Reap et al., 2008)

Requires more data to include

avoided products (Ekvall and

Finnveden, 2001; Reap et al., 2008;

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It is commonly affirmed that the choice of method depends on the type of the study:

attributional or consequential. Allocation should be used in the first case, while allocation

should be avoided by system expansion in the latter (Baumann and Tillman, 2004;

Curran, 2007a; Schmidt, 2008b; Thomassen et al., 2008a; Fruergaard et al., 2009).

Previously, it had been suggested that system expansion should be used always

(Weidema, 2001), and economic allocation had also been perceived as a universal

solution (Ekvall and Finnveden, 2001; Guinee et al., 2004).

Different co-product handling methods are one of the reasons for different results and

non-comparability among studies of similar products (Azapagic and Clift, 1999b; a;

Cederberg and Stadig, 2003; Heijungs and Guinee, 2007; Reap et al., 2008; Cherubini et

al., 2009; Flysjö et al., 2011a). However, results with different methods for allocation are

not always radically different (Curran, 2007b; Guinee and Heijungs, 2007). In the literature

authors sometimes choose to evaluate the sensitivity of results with different allocation or

system expansion methods. Essentially the evaluation of sensitivity to co-product handling

methodology should be seen as a way to provide robustness to the LCA study process.

Recently, the issue of comparability among studies also has been prompted. Flysjö et al.

(2011a) analysed different guidelines for co-product handling and has stated the need for

harmonization between life cycle approaches studies. This is a critical issue if the results

of life cycle studies will be used in communications.