Proper or messy allocation?--Systematic approach to identifying and solving multi-functionality in LCA

• Avoided burden¹
  

• Most existing LCA databases today do not include multi-functional processes.

  • including ecoinvent

• MF is ‘solved’ by database developers by delivering only mono-functional datasets.

• Mostly, practitioners cannot change this methodological decision anymore and often don’t realize that they are handling (‘accepting’) more MF issues than they realize.

• Consequently, most software doesn’t include ways to address MF.

• While it is known as one of the most determining factors of LCA results.

  • Certainly, in the increasing number of CE and symbiosis applications of LCA

• And most published literature remains vague on MF details too.

  • Non-transparent reporting of MF; claiming to have no or just 1 MF issue while also the (pre-allocated) ecoinvent database is used for example.

4 steps approach

Most LCA case studies so far apply one of the solutions without properly justifying where and what exactly the multi-functionality problem is and which criteria are used for determining that.

Therefore, we developed a 4 steps approach, explicitly distinguishing these steps, aiming for more transparency in the discussion on multi-functionality approaches and solutions.

We first need to define the problem

• Multi-functionality (MF) = the problem
• Allocation = one of the solutions
  • partitioning the inputs and outputs of unit processes among products systems.

What is MF

• These are processes which have more than one functions.
  • “multifunctional processes”

Definitions

Economic Allocation: Examples and Derived Decision Tree
Jeroen B. Guinde*, Reinout Heijungs and Gjah Huppes
https://link.springer.com/content/pdf/10.1007/BF02978533.pdf

• Economic flow: a flow of goods, materials, services, energy or waste from one unit process to another, with either a positive (e.g. steel, transportation) or zero/negative (e.g. waste) economic value.

• Functional flow: any of the flows of a unit process that constitute its goal.

  • goods (products outflows) of a production process
  • waste inflows of a waste treatment process
  • every process needs at least one functional flow; even use/consumption processes (often delivering the FU/reference flow as functional flow)
  • A flow is not intrinsically a functional flow, but only with respect to a certain unit process (more specific: an outflow that is a functional flow for one unit process is a non-functional inflow for one or more other unit processes. An inflow that is a functional flow for a specific unit process is a non-functional outflow for one or more other unit processes)

• Non-functional flow: any of the flows of a unit process that are not a functional flow.

  • product inflows and waste outflows, as well as elementary inflows and outflows (natural resources and pollutants)

Systematic approach

Step 1: What are the good and waste flows of every process?

• To distinguish products from wastes, any criterion can be used if it supports determining which flows constitute the goal of a process and can be applied consistently for all processes.
• Basically, all LCA practitioners use economic value for this:
  • Good/product (G) is a flow with an economic value >= 0;
  • Waste is a flow with an economic value < 0.

Step 2: What are the functional flows of every process?

• The functional flow(s) of each process are either products that are produced by a process or wastes that are treated by a process (others see above).
  

Step 3: which processes are multi-functional processes?

Step 4: How to resolve the problems related to that?