Bioenergy and bio-based products for the circular economy
According to the IEA, “Bioenergy is energy derived from the conversion of biomass where biomass may be used directly as fuel, or processed into liquids and gases.” Examples include heat from wood pellets, electricity from biogas produced from food waste or crops, and electricity from combustion of straw or miscanthus. Policies to improve security of energy supply and reduce dependence on finite and polluting fossil fuels, exemplified by the Renewable Energy Directive, have been a major driver of the expansion of bioenergy across the EU over the past decade.
Simultaneously, the Circular Economy Strategy is driving the use of bio-based products that can be recycled within biological cycles. A European standard defines “bio-based products” as “products wholly or partly derived from biomass, such as plants, trees or animals (the biomass can have undergone physical, chemical or biological treatment)”. Examples of bio-based products include egg cartons made from grass and recycled paper, and compostable bags made from polylactic acid derived from maize.
Whilst the aforementioned strategies are generally well targeted to improve the sustainability of our economy, they do place additional pressures on farming, and agricultural land resources, to produce the necessary bio-feedstocks. The production of such bio-feedstocks may sometimes be in competition with food production (see Popp et al., 2014), leading to possible “carbon leakage” by displacing food production via international trade (Searchinger et al., 2008). This has led to increasing scrutiny of bioenergy and bio-based products, invoking questions including:
- Are bio-based products more sustainable than conventional products they replace?
- How much land do they require?
- Do they reduce or increase greenhouse gas (GHG) emissions that cause climate change?
- Do they contribute to air and water pollution via leaky nutrient cycles?
- How effective are they at sparing finite resources?
Life cycle assessment
Life cycle assessment (LCA) is a rigorous, scientific approach that can be applied to answer such questions based on methodology defined by the International Standards Organisation (ISO 14040; ISO 14044) and, for related carbon foot-printing, by PAS 2050. LCA quantifies the environmental impact (potential) over the life cycle of a product or service. An example is the carbon footprint, expressed as kg CO2e (climate impact potential) of generating one kWh of bio-electricity. LCA may be applied to:
- Benchmark the environmental intensity of bioenergy and bio-products against replaced conventional energy and products
- Identify production strategies that minimise environmental impacts and thus improve the sustainability of such products
Farm stage “hotspots”
Cultivation of bio-feedstocks on farms is usually the hotspot stage in bioenergy and bio-based product value chains, giving rise to the largest share of environmental impact. Agriculture, forestry and land use change account for approximately 25% of global GHG emissions (IPCC, 2014), and approximately half of humans’ wider ecological footprint. This reflects the loss of large amounts of carbon from vegetation and soils when land is converted to agriculture, leaky cycling of nutrients (see the excellent video on nitrogen impacts made by the European Nitrogen Assessment), and the extraction and manufacture of inputs such as fertilisers. Figure 1, below, shows that wood heat has less impact on global warming, fossil resource depletion and acidification than oil heat, but may have a greater impact on eutrophication (nutrient enrichment of waters) than oil heat. The latter impact is highly dependent on farm management and landscape context of willow cultivation; application of fertiliser leads to relatively high eutrophication burdens, whilst planting willow on buffer strips next to rivers can “mop up” nutrients lost from neighbouring food production.
Figure 1. Environmental burdens of heat from wood chips produced using willow cultivated in different ways, and from oil. Source: Styles et al. (2016)
Consequential LCA is an increasingly popular form of LCA that expands system boundaries to consider marginal direct and indirect changes incurred by a particular intervention, such as the introduction of bio-feedstock production into a farm system. In a recent study (Styles et al., 2015a) we applied consequential LCA to demonstrate that the introduction of a biogas plant into a large dairy farm to generate electricity from slurry, grass and maize can lead to substantial carbon savings by avoiding emissions from slurry storage and grid electricity generation, but also entails significant risk of large carbon leakage from indirect land use change caused by displacement of cattle feed production to other countries (e.g. soybeans from Brazil). Subsequently, we also found that GHG emissions from indirect land use change potentially caused by establishment of maize monocultures on arable farms to supply large crop-fed biogas plants can outweigh GHG savings from avoiding grid electricity generation. However, if maize is established on small portions of multiple farms as a break crop, optimisation of food crop rotations can mitigate this possible land use change effect (Styles et al., 2015b). Most of the bioenergy carbon calculators available online (e.g. Biograce) do not consider indirect effects, although the excellent Biomass Emissions And Counterfactual model produced by DECC does consider the counterfactual fate of feedstock that is used for bioenergy, such as US forest residues used to substitute coal in the Drax power station.
Would you like to learn about LCA methodology?
A part-time MSc module on Carbon Foot-printing and Life Cycle Assessment will be delivered entirely online by Bangor University from January through to April 2017, drawing on freely available online calculators and the latest research to demonstrate application of LCA to evaluate bioenergy and bio-based product value chains, and their interaction with food production. This module is part of the Industrial Biotechnology MSc, and BBSRC Advanced Training Partnership. Anyone wishing to enrol on the full Bangor or Aberystwyth MSc courses that this module sits within may also be eligible for the new English postgraduate loan. Registration now open, until 6th January!
See also the module on On-Farm Anaerobic Digestion (AD) – May 2017