1 - Biomass production

Characterising a biomass resource

The first thing we may think of are the chemical and physical properties of the biomass. These can be determined by sending a sample of biomass for laboratory analyses. Alternatively, data can be found in existing litterature and databases.

For practice, other practical aspects need to be considered to fully characterise a biomass resource:

• How wet is the feedstock? It is very dry (<10%), rather wet (around 50%), or very wet (>60%)? High moisture levels affect for instance storage, transportation or pre-treatment requirements.

• Is it a problematic or heterogenous feedstock? For instance, the composition of garden waste is known to vary from one place to another, but also in time. Beach cast (algae collected from beach cleaning operations) can be mixed with varying amounts of sand, which is a challenge for some industrial processing techniques.

• How much and when is the biomass available? Is the biomass harvested continuously over the year, or only once a year in a given season. Can it be easily stored, for a continuous supply?

• Is it primary or waste biomass? Although it is a subjective and changing notion, we commonly hear that biochar can be produced from waste biomass as opposed to primary biomass. Waste biomass is sometimes referred to as secondary, by-product, or side-product biomass. Waste biomass is seen as an undesired product for a given stakeholder. Primary biomass is also referred to as cultivated biomass or dedicated biomass. Primary biomass is the main output of an activity.

The distinction between waste and primary biomass is used to emphasize that using waste biomass has limited environmental impacts, does not affect land use. In fact this claim refers to a subtle notion in environmental systems analysis & life-cycle assessment, a notion called the reference land or biomass use. More about this in the next section.

LCA of biomass production and supply

Environmental impacts arise from consumption of products and services, the use of natural resources, and their effects on the environment. Assessing the environmental impacts of biomass production is a dedicated field of research because of its many specifities (e.g. biogenic carbon flows and stocks, direct and indirect land use effects, timing of emissions, crop rotations, stand and lanscape perspectives).

The cradle-to-gate LCA of biomass production and supply should include (but not limited to) the following items:

1. Supply-chain activities

For crop cultivation or forestry operations (e.g. willon cultivation on cropland):

• Machinery and fuel use for e.g. land preparation, harvesting, irriguation
• Manufacturing and disposal of machinery and infrastructure
• Production of fertilisers, other agrochemicals and consumables
• Emissions arising from fertilisers use
• Transportation of the biomass, including fuel emissions and road infrastructure emissions

For waste or secondary biomass (e.g. municipal garden waste):

In this case, it is common to apply a “cut-off” approach. This implies that the no environmental burdens are attributed to the waste biomass for its creation. All upstream burdens are attributed to the main product. However, any operations taking place downstream of the waste creation are considered.

This typically includes:

• Collection of the waste biomass
• Storage & handling at the waste collection site
• Emissions arising during storage

Remark: The case of multi-product biomass production:

When an activity produces several biomass products, the LCA practionner is facing an issue of attributing the production burdens between the products. Two main approaches can be followed, both being a subjective choice:

• If one product is considered as the main product, and the others have little value: all production burdens are attributed to the main product. The co-products are considered burden free (so called cut-off approach for by-products).

• If all products are deemed having some value, an allocation of the burdens based on some physical property can be performed.

Both approaches are valid and have been applied to the same feedstocks in different studies.

For instance, in a study by Hammar & al (2015) logging residues are considered a side-product from conventional forestry operation for timber production. Only impacts from harvesting, chipping and transportation are considered (alongside direct land use change). However, in the ecoinvent life cycle database, forestry operations are considered as a multi-functional activity delivering multiple products: timber, bundle energy wood, and woodchips. An allocation of burdens from forestry operation is applied between the three products (dry mass allocation?).

Remark: Biomass production involving use of another biomass

What if to produce wood, we use biofuels made from wood via a fischer-trop process? That’s what we call a loop in LCA. It can be solved but makes calculations sometimes more complicated than if we assume that fossil fuels are used in the supply-chain.