M1: Terminology, system definition, indicator element, and procedure of MFA

Question 1

What are the two main types of MFA?

Answer 1

Bulk MFA (Material flow accounting)

• Standardized system definition –> comparative analyses
• Analysis of all materials of an economy (aggregated)
• Country scale

Substance flow analysis (SFA)

• Individual system definition –> problem oriented
• Analysis of specific materials AND substances
• Various scales

Question 2

What is a “Substance” in MFA?

Answer 2

• Any chemical element or compound composed of uniform units.
• All substances are characterized by a unique and identical constitution and are thus homogenous
• Examples: Cd, C, Ag, CO2 , NH 3
• Wood is not a substance because it contains a lot of different compounds.

Question 3

What are “goods” in MFA?

Answer 3

• Economic entities of matter with a positive or negative economic value.
• Goods are made up of one or several substances.
• Examples: drinking water, TV sets, automobiles, garbage, sewage sludge
• The air that we breath can be a good (it depends on the case). But in general you can’t set a economic value on air. In other cases it is seen that people sell compressed air in cans.

Question 4

What is a “Process” in MFA?

Answer 4

• Balance volume.
• Transformation, transport, storage of goods/substances.
• Examples: human body, private households, manufacturing plant

Question 5

What is a flow and a flux?

Answer 5

Flow

• Amount of a good or substance per time (rate).
• Examples: total water consumption in Denmark (kg/a)

Flux

• Amount of a good or substance per time (rate) per cross section.
• Examples: per capita water consumption in Denmark (kg/(cap*a))

Question 6

What is a stock in MFA?

Answer 6

• The mass of a material residing in a process or system during the balancing period of the system.
• Likely to change overtime, especially with human activities.
• Examples: buildings, car fleet, mobile phones , wastes in landfills

What about beers in your fridge?
- Beers in the fridge can both be a flow and a stock –> it depends on the context.

Question 7

What is a system?

Answer 7

General:
- Group of elements and interactions between these elements

MFA:

• Elements are processes.
• Interactions are flows of goods.
• Examples: human body consisting of organs…,

What about a factory?
- A factory can both be a process (if we look in a hugh point of view. A factory can be a process in the society) and a system (if we look in a smaller point of view and only look at the single factory).

Question 8

What is a activity?

Answer 8

• Basic human needs
• Includes all relevant stocks and flows, processes, goods, and substances to fulfill the need.
• Examples: to nourish, to clean, to reside and work, to transport and communicate

Question 9

How is a system defined in text?

Answer 9

• The system is the actual object of an MFA investigation It is defined by a group of elements, interaction between these elements, and the boundaries between these and other elements in space and time
• Elements are processes.
• Interactions are flows of goods
• A single process or a combination of several processes can represent a system

Question 10

What is a system boundary?

Answer 10

Definition of the system in time and space:

• Temporal boundary the time span over which the system is investigated and balanced.
• Spatial boundary usually fixed by the geographical area in which the processes are located.

Question 11

What is an indicator element?

Answer 11

• An indicator element represents a group of substances.
• It shows a characteristic physical, biochemical, and/or chemical behavior that is a specific property of all members of the group.

Example:
Atmophile elements (e.g., Cd, Zn, Sb, Pb) have lower boiling point
- In a combustion process, atmophile elements are transferred to off gas.
- Cd may serve as an indicator for this group

Lithophile elements (e.g., Ti , V, Cr, Fe, Co, Ni) have higher boiling point

• In a combustion process, lithophile elements remain in bottom ash or slag.
• Fe may serve as indicator for this group

Question 12

Mention other indicator elements

Answer 12

Organic carbon is the most important carrier of energy (e.g., in food, wood, fossil fuels…)
- A regional carbon cycle is therefore suitable as a first approximation for a regional energy balance (e.g., examine energy potential of biomass).

Phosphorus is usually the growth limiting nutrient in aquatic (freshwater) systems.
- A regional phosphorus cycle might therefore be useful for a first examination if eutrophication problems are of concern.

Chlorine forms with organic molecules C Cl bonds (e.g., PCB s, dioxines)
- A chlorine cycle might shed light on the sources of PCB and dioxin emissions.