IN RECENT YEARS, Canada has pumped billions of dollars into its biofuel industry. Most notable have been incentives paid to farmers to grow corn for ethanol production. While Canada now has a nascent biofuel industry with more and more plants opening across the country, little thought has been given to the ecological consequences of a shift from petroleum to bioenergy fuels. Instead, the discussion has centred on food-versus-fuel and climate change. While these issues are important, by focusing on them too closely, one risks missing the proverbial forest.
Bioenergy is about the sustainable extraction of useful energy from an ecosystem, and, well, ecosystems are pretty complex. They don’t, for example, often operate in a linear fashion, and can sometimes jump from one state to another, a process known, illustratively, as “flipping attractors.” What was once a beautiful pristine lake can fill with unwanted algae, seemingly overnight. Furthermore, we often don’t know why ecosystems flip attractors. For example, we still can’t explain why bee colonies all over North America are suddenly committing suicide. To compound matters, once a complex system sets out on a new path, it is often hard to turn it back. This, in part, is why fighting climate change will be so difficult.
Given that powering our country or world with bioenergy will have profound effects on ecosystems, we risk consequences that are difficult to predict. As a result, it would be wise to tread carefully. We need to determine how we can harvest useful energy from ecosystems without impairing their function, or the function of the large, complex global biosphere.
To achieve this result, we need to consider some general properties of ecosystems. Disrespect them and you impair their function.
Property 1: Ecosystems self-organize around energy gradients
The most important of the three properties discussed in this article is that self-organizing systems arrange themselves along energy gradients. If there is no source of useful energy, a system cannot self-organize. This property operates on a number of different scales: from the bacterial colonies that grow in petri dishes, to Alberta’s economy, which has organized itself around the tar sands.
There are two ways to use this first property when evaluating the impact that harvesting bioenergy will have on an ecosystem. The first method deals with our choice of feedstocks and their associated ecosystems. When extracting bioenergy, we can choose to interact with systems at different levels of maturity and embodied bioenergy. For example, we can select switchgrass from an immature field or trees from a developed forest. Harvesting switchgrass might appear to be the more sustainable option given that deforestation is a more obvious and severe disturbance. But by harvesting switchgrass, we prevent the grassland ecosystem from developing to a higher level of self-organization with more bioenergy and increased ecological benefits (such as greater biodiversity). Based on an ecosystem approach, it may make more sense to interact with the grassland at a later stage.
The second method of applying the first property is by taking advantage of the nature of self-organization. By providing an energy gradient around which self-organization can occur, it is possible to have ecosystems produce bioenergy. For example, when bacteria self-organize around the energy found in manure, they produce biogas and eliminate the waste product. Many waste products in human society have the potential to serve as energy gradients.
Property 2: Ecosystems prefer closed material cycles
The second property of ecological self-organization is that ecosystems tend to keep their material cycles closed. In other words, they try not to leak material. For example, the Amazon rainforest has its material locked up in a perpetual cycle of growth and decay. The soils are thin and any biomass removed from this system may effectively be lost for good. In practice, it is impossible for an ecosystem to maintain a completely closed material cycle – species may enter or leave the rainforest, and the rainforest is constantly exchanging matter with the atmosphere through photosynthesis and respiration. However, it is generally true that the more difficult it is for a system to maintain a closed material cycle, the more vulnerable it is to environmental disturbances.
Some bioenergy technologies are able to derive energy without turning the feedstock into useless waste products, as opposed to what happens when, for example, you burn the feedstock. Systems that separate their energy and material pathways are better able to maintain a closed material cycle. Examples include technologies that produce biogas, ethanol and biodiesel. In each case, only the product of the energy pathway is incinerated, leaving the material cycle more intact.
Property 3: Temporal and spatial scales
The third property is that self-organization occurs at different timescales and over varying areas, concepts that are commonly referred to as temporal and spatial scales, with each scale controlled by its own processes, laws and feedback. To understand the importance of feedback, think of pain. Pain provides indispensable feedback. Generally, slight pain in the short term spurs a response that could prevent major harm in the long run.
To understand variations in temporal and spatial scales, let’s compare rabbits to forests. While both a rabbit and a boreal forest are self-organizing systems, the boreal forest is a much larger and older system. What may be constant over the lifetime of the rabbit can be quite variable over the lifetime of the boreal forest (e.g. atmospheric carbon dioxide concentrations). Consequently, we need to ensure that we are receiving feedback in the appropriate time frame.
This third property – that self-organization occurs at different temporal and spatial scales – is harder to apply as an indicator than the first two because it depends on the specific bioenergy technology, as well as the manner and extent to which the product of that technology is used. However, it can help us evaluate different methods of using bioenergy. For example, most bioenergy – from wood to biogas – is eventually burned. Unfortunately, combustion opens the material cycle, because most combusted material is lost to the atmosphere (as carbon dioxide and other gases). Essentially, combustion forces a system to operate at a scale that is both larger (the entire atmosphere) and longer (burned material is effectively lost so it takes the ecosystem more time to mature).
These three properties of ecological self-organization give us the means to look beyond the discussion of food-versus-fuel and climate change. They allow us to determine if we can use a particular bioenergy technology to harvest useful energy without impairing the ecosystem’s function, and the function of the large, complex global biosphere.
Bioenergy technologies fall into two categories: physicochemical and biological. Physicochemical pathways include drying, transesterification, biomass gasification and others. They convert bioenergy into useful energy through a combination of pressure, heat and chemical reactions. Biological pathways include anaerobic digestion and fermentation. They harness bioenergy by exploiting the ecological self-organization of bacteria and micro-organisms. The accompanying table describes the majority of bioenergy options currently available.
Physicochemical pathways are generally less complex than biological ones because they don’t depend on living systems for the energy conversion step. The simplest physicochemical pathway involves drying a variety of biomass feedstocks, including grasses and wood, followed by burning to produce heat or electricity. Since drying does not separate material and energy pathways, everything is burned, which opens the material cycle.
A second physicochemical pathway is transesterification, which is used to produce biodiesel. Transesterification is a chemical process during which oil from sunflower seeds, canola or chicken fat, for example, reacts with methanol and sodium hydroxide to form biodiesel and glycerine. The biodiesel can be combusted for heating, transport or electricity, or used in a fuel cell, and most of the by-products can be utilized as animal feed, biogas or compost. Unfortunately, biodiesel often involves harvesting bioenergy from immature ecosystems, such as monocropped palms or high-density algae ponds, and requires methanol, a fossil fuel input.
A third physicochemical pathway, biomass gasification, is the combustion of biomass in an oxygen-free environment. The gasification process breaks apart wood to produce an energy-rich gas commonly called synthetic gas or syngas. Syngas can be burned for heating, electricity or transport purposes, or it can be used in a fuel cell. Gasification can draw from a diverse array of biomass feedstocks; however, there is little that can be done with its by-products (fly ash, nitrous oxides, sulphur dioxide and tar). As a result, the combustion of syngas opens the material cycle.
Biological energy pathways
Biological energy pathways use ecological self-organization of communities of micro-organisms to produce bioenergy. This natural, though somewhat complex process involves a more closed material cycle since it separates energy (which is usually burned as a fuel) and material pathways. Furthermore, the waste products resulting from biological pathways are more likely to have a use than their physicochemical counterparts, which makes them more ecologically friendly.
While there are several biological pathways, they all involve anaerobic decomposition. Anaerobic (without oxygen) decomposition produces end-products that contain available energy, and are generally easier and safer to use than the original feedstock. For example, it’s cleaner to burn methane than the manure from which it is derived.
Anaerobic digestion can be used to produce a mixture of methane and carbon dioxide, known as biogas. The biogas can be combusted for electrical, transportation and heating purposes, or used in a fuel cell. There are several advantages of anaerobic digestion. First, it separates energy and material pathways. Second, it draws from a diversity of feedstocks, including manure, agricultural crops and residues, and municipal organic wastes. Finally, the material pathway, a microbial biomass, is a natural fertilizer.
The disadvantage of anaerobic digestion is that the most common feedstock, animal manure, is often drawn from intensive livestock operations, which are immature ecosystems since they produce animals for slaughter in much the same way as field crops are cultivated. But as a means of reducing wastes, anaerobic digestion is appealing.
Another biological pathway is fermentation, the anaerobic decomposition of sugar by yeast to produce ethanol. Fermentation is the pathway used to produce ethanol from corn. Ethanol may be combusted for electrical, heating and transportation purposes. One advantage of fermentation is that the material pathway produces a product, fibrous material, which has multiple end uses, including composting and animal feed. The principal disadvantage of fermentation is that it also draws from immature agricultural ecosystems (generally monocropped plants such as corn or sugar cane).
The second generation of fermentation technology, often called cellulosic fermentation, involves producing ethanol from woody material. It overcomes the limitation of first-generation fermentation because it can draw from a more diverse array of biomass feedstocks, including more mature ones. However, the increased physicochemical processing required to prepare the feedstock for secondary fermentation results in the production of waste products that are more difficult to recycle. Furthermore, second-generation fermentation opens the material cycle in a bigger way than primary fermentation.
There is no categorically right or wrong biofuel, but when the impact on the ecosystem is considered, anaerobic digestion outperforms the other pathways. Yet use of anaerobic digestion remains almost entirely untapped in Canada. It seems that by limiting our focus to specific issues, such as the food-versus-fuel debate and greenhouse gas emissions reductions, Canada may be missing an opportunity. If we are to successfully shift from a petroleum-based energy system to a biological one, we need to look at the forest as well as the trees.
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