Energy from biomass in the UK: sources, processes and biodiversity implications

The concept of using biomass (organic material) as fuel is hardly new. Wood has been used as a fuel for many thousands of years, and is still the main source of heat energy for millions in the developing world. Recent developments in the renewable energy sector in both developed and developing nations have catalysed the consideration of how different forms of biomass can be produced and processed and used to provide different forms of energy. This paper summarizes the main potential biomass sources, processing methods and end-products that could be developed and produced in the near future within the UK and the rest of Europe. It considers some of the major impacts of such developments on biodiversity. There are a wide range of other potential environmental impacts from the development of different biomass technologies, including effects on air quality, hydrology, soil chemistry, landscape value, local economies and human communities. These are not considered in detail here. The total UK energy demand is split almost equally between three energy uses that overlap only to a small extent: transport, heating and electricity. Currently, all three of these, but particularly transport and heating, rely heavily on fossil fuel energy sources. Unlike other forms of renewable energy such as wind or wave power, which can only generate electricity, biomass has the potential to provide energy source for all three sectors, by using different biomass sources and processing methods. Organic material can be used in one of two main ways as an energy source – it can be either directly combusted to produce heat and/or electricity, or processed into a secondary fuel source (liquid or gas), which can then be combusted. Liquid biofuels can be used as replacements for mineral diesel or petrol (bio-diesel and bio-ethanol). Gas products include methane and hydrogen. A range of biomass sources, processing methods and end-products is shown in Table 1. See Fergusson (2004) for more detailed discussion of the various production processes and their energy and carbon implications. The raw biomass materials listed are some of those most likely to be available on a large scale in the short to medium term within Europe. Many potential sources of biomass energy are already grown for other purposes, or are otherwise already available, in large quantities, in the UK and Western Europe as a whole (e.g. wheat, oilseed rape, sugar beet, forestry waste, straw, waste oils). Hence, there is no new technology or large-scale expansion required to produce these raw fuel materials. Other biomass sources, such as perennial woody or grass crops, have yet to be grown on a widespread commercial scale, but the crop production technology is well advanced. There are many other possible sources of biomass, including several feedstocks that could be easily imported into Europe, including palm, soya and sunflower oils (for bio-diesel), sugarcane (for bio-ethanol), and palm or coconut husks (for direct combustion). Combustion, esterification and fermentation technologies are already fully available in a technical sense. Hydrolysis and gasification methods are currently only at the demonstration stage for use with biomass material but offer greater efficiencies and carbon benefits in the longer term. One potentially important benefit of the gasification process is the possibility to produce kerosene, used as aviation fuel. This is currently the only option available to produce aviation fuel not based purely on fossil fuel sources, an important consideration given the high and growing contribution of air travel to carbon emissions. Production of bio-diesel and bio-ethanol can also yield useful co-products, including animal food and products for the chemical and pharmaceutical industries. Small proportions of organic matter can be used by existing fossil-fuel-burning power plants (‘co-firing’), with only modest technical alterations required. By contrast, large-scale, widespread, dedicated biomass-burning or processing plants do not yet exist in the UK, although some other European states are more advanced in this regard. Aside from the long-term beneficial effects of reducing carbon emissions and hence ameliorating climate change, the development of biomass energy is likely to have more direct effects on biodiversity, potentially both positive and negative (Anderson et al. 2004). Where land-use change results from growing dedicated biomass crops, biodiversity is likely to be affected. By contrast, use of existing waste or co-products for bio-energy purposes is much less likely to result in significant direct effects on biodiversity. The overall impact of developing a particular biomass energy crop will depend on a combination of effects, operating at different spatial scales (Anderson et al. 2004): the intrinsic biodiversity value of the crop itself, dependent on crop species, vegetation structure and crop management; the biodiversity value of the crop relative to alternative land-use types which it replaces; landscape-scale effects – the geographical location, scale of development and spatial distribution of these crops. It will be impossible to predict the full effects of biomass crop development on biodiversity without considering all these issues. Intrinsic biodiversity value may depend largely on crop management systems. For example, an extensively managed perennial woody or grass energy crop may support diverse plant and invertebrate communities (Coates & Say 1999), whereas crops under more intensive management regimes, involving herbicide and pesticide use, may not. Resumption of traditional management techniques within semi-natural woodlands to provide wood biomass may also result in biodiversity benefits, but large-scale clear-felling of these habitats for the same products is highly likely to be damaging overall. In comparison with conventional arable crops, large-scale short-rotation willow coppice plantations can provide benefits for some taxonomic groups, e.g. bird species typical of rank herbaceous vegetation, scrub and young woodland (Sage et al. 2006), butterflies and flowering plants (Cunningham et al. 2004). Perennial grass crops may also provide some wildlife benefits compared with conventional intensively managed farmland (Semere & Slater 2005) but as commercial-scale plantations are not yet widespread in Europe, ecological assessment data are currently sparse. However, if more marginal, less intensively managed land is replaced by biomass crops, then effects on overall biodiversity are more likely to be negative. This effect could take place in Europe, where set-aside land, known to provide significant benefits to farmland wildlife (Van Burskirk & Willi 2004), is a potential target area for biomass or biofuel crops. Development of a market for forestry wood as a biomass energy source could provide initial biodiversity benefits if this resulted in the removal of non-native conifer species from extensively managed open land (e.g. moorland or heathland) in Europe. However, these positive effects would be reversed if the market for this wood encouraged replanting or new plantings of the same species in the same habitats. Highly damaging effects will also take place further afield if the demand for biofuels results in high-biodiversity habitats, such as tropical forest, being replaced by crops such as oil-palm, soya or sugar cane grown for export. Rapid, large-scale clearance of natural forest for oil palm plantations has already occurred in Southeast Asia, and continues apace (Clay 2004, Hansen 2005). The development of the biofuel industry has the potential to exacerbate this situation. The useable energy per unit weight of most raw biomass material is low compared with other non-renewable energy sources (e.g. oil, coal). This is likely to have two main consequences: Very large quantities (possibly running into millions of hectares) will be required to provide a significant proportion of national energy demand from biomass (Eyre et al. 2002, Bullard et al. 2003, RCEP 2004). This will necessitate very large areas of land being given over to biomass production from other purposes. For conventional arable crops such as wheat and oilseed rape, this may be possible, to an extent at least, without major changes in land use, although the food crops replaced may be grown elsewhere with consequent knock-on effects. Large-scale development of perennial woody or grass energy crops, or novel annual arable crops, will represent landscape-scale changes in land-use type, however. This will inevitably have some effect on biodiversity on a similar scale. The costs of transporting the raw biomass material are likely to have a significant impact on overall crop economics, thus limiting the distance over which biomass can be economically transported between source and end-use locations. Therefore, there may be strong economic pressure for processing or combustion facilities to be surrounded by large-scale monocultures of biomass feed stocks to maximize the economic benefit of the crop. If habitat diversity is reduced in these areas as a result, the overall effects on biodiversity in these areas are likely to be negative. There are many possible ways in which biomass could be used to provide energy, involving a wide range and diversity of biomass types, and processing techniques. Which of these source/process combinations is developed on a large scale in the future will depend largely on political and economic drivers. The ultimate driver for the development of biomass energy should be the net reduction of carbon emissions. No biomass energy sources are truly carbon-neutral, as the production, transportation and processing stages all involve some degree of non-renewable energy consumption. Agricultural inputs (fertilizers, pesticides), biomass transportation distances and proportion of energy lost during processing and combustion methods will play significant roles in determining the overall carbon balance of biomass energy sources. It will be desirable to minimize all these to achieve maximum overall environmental gain from biomass energy. Appropriate economic drivers, created through political will, will be essential to this outcome. Biodiversity impacts can vary enormously according to the biomass feedstock used and the location and the manner of its production. This is a complex area about which our understanding thus far is rather limited. None the less, it will be important that future energy policies also take account of global biodiversity considerations, as these could be far-reaching. Safeguards must be put in place to protect biodiversity-rich habitats.