Elsewhere in Science: We need to talk about biofuels

Not sure why we haven’t talked about this yet. One of the core themes of RoboPlant is getting energy from plants, and it took me a while to realise there was a big elephant in the room labelled ‘biofuels’ in big green letters. As you may be aware, natural photosynthesis enables solar energy to be packaged into storable chemicals (e.g. sugars). Biofuels are liquid fuels which are derived from these chemicals, and can be used in combustion engines to power vehicles in the same way as petroleum. They sound like a great idea on paper, for sure, but what’s the catch? In this article we’ll explore a little about what biofuels are, why they’re controversial, and why recent technological developments may mean pond scum could soon save the world.

The process of producing conventional biofuels involves fermenting plant matter using bacteria. The bacteria produce ethanol as a by-product of respiration in the absence of oxygen, and this ‘bioethanol’ can be used directly as a fuel or as a fuel additive. Alternatively, bioethanol can be combined with vegetable oil (or other natural lipids) to produce biodiesel, which has become very popular in the last couple of decades. It’s a bit quicker than petroleum production, which takes several million years. Biodiesel is also a lot cleaner than petroleum, as it doesn’t contain the unnecessary environmentally damaging components found in petroleum, like sulphur (which causes acid rain when it’s released into the atmosphere). Biodiesel also emits up to 75% less carbon dioxide when burnt.

Biodiesel has already proved itself as an effective vehicle fuel. Image credid: rael.berkeley.edu

Biodiesel has already proved itself as an effective vehicle fuel. Image credit: rael.berkeley.edu

Furthermore, because plants take in carbon dioxide when they photosynthesise, this theoretically offsets the carbon that is put back into the atmosphere when the fuel is burnt, so biofuels are carbon-neutral, right? Wrong. In theory, this is correct, but the situation in the real world is not so dandy. Ironically, the popularity of biodiesel has led to swathes of rainforest being chopped down, and in some cases the eviction of local people to make way for biofuel plantations. For example, swathes of south-east Asian peat forest have been burnt in recent years to make way for palm oil plantations, releasing 100-200 tonnes of carbon dioxide per hectare. It’s been estimated that it will take 200 years for the palm oil’s photosynthesis to offset the damage caused by establishing the plantations in the first place. Biofuels also compete directly with food production, driving food prices higher. As of 2011, 40% of corn in the US goes into biofuels, and the higher prices incurred by this are suffered most by third world countries which import the corn, among them Kenya, which is already heavily poverty-stricken.

Image credits: oxfamblogs.org; teenbiotechchallenge.ucdavis.edu; politicalhumor.about.com; filipspagnoli.wordpress.com

Image credits: oxfamblogs.org; teenbiotechchallenge.ucdavis.edu; politicalhumor.about.com; filipspagnoli.wordpress.com

Biofuels derived from food crops – referred to as first generation biofuels – are therefore not the answer. In fact, I would go as far to say that they constitute one of the greatest ironies in the history of environmentalism. But the concept of getting fuel directly from plants is still a pretty neat idea, so what else can we do?

Second generation biofuels refer to liquid fuels derived from non-food crops, like miscanthus grass. Recent research has focused on making ethanol from lignocellulose – the main structural carbohydrate which is found in just about any plant you can name which has a stem. Ruminants like cows can naturally digest lignocellulose in their guts, but the enzymatic processes that break it down are complex and very difficult to replicate in the lab. If we could do it, however, it would allow us to squeeze as much fuel as possible out of every nook and cranny of the crop, and even use agricultural waste, saving huge amounts of arable land. But there’s the snag – it would still rely on arable land, which is likely to be needed more and more in the coming years to supply a rising world population with food.

Let us therefore turn our attention away from plants, and instead take a look at microalgae – which some may know better as ‘pond scum’. These tiny, green, photosynthesising blobs have been around for over 3 billion years, and were the original precursors to plants. Today, they herald in the third generation of biofuels, as they photosynthesise to produce lipids (fats) which can be used to generate biodiesel. Algae do not need arable land to grow – just water, and because they are not picky about the water they live in, they can be grown in waste water. There are many species of algae which produce varying amounts of lipids, carbohydrates and proteins, so different species and strains can therefore be utilised for different purposes. Some produce up to 50% of their mass in fats which can be used to make biodiesel, and can produce up to 50 more oil per acre than corn.

Microalgae farming systems for biodiesel production. Left: Small scale photobioreactors for incubation; right: open pond system for large scale production. Image credits: solar.calfinder.com; nature.com

Microalgae farming systems for biodiesel production. Left: Small scale photobioreactors for incubation; right: open pond system for large scale production. Image credits: solar.calfinder.com; nature.com

There are many ways algae can be farmed. Conventionally, an ideal, high-oil producing strain is isolated in the lab, and then sent outdoors to grow in huge open ponds. Alternatively, they can be grown under controlled conditions in enclosed tubes called ‘photobioreactors’. The latter are generally more efficient as they are less prone to contamination by bacteria and other algal strains which may compete with the strain we want, but they are also more expensive. Nevertheless, a lot of funding is currently going into the research and production of algal biodiesel, as it could potentially replace petroleum as the transport fuel of the not-too-distant future. One of the major advantages is that it can be distributed using the existing transport and distribution infrastructure, so it doesn’t face one of the major hurdles faced by the proposed hydrogen economy.

Algae have been gaining a lot of steam in the renewable energy race in recent years. The San Diego-based company Sapphire Energy raised over $100 million in investments in 2008 to produce ‘green crude’, with the help of Bill Gates, the Wellcome Trust and others. Other, similar solutions being tossed about include deriving fuel from macroalage (better known as seaweed) grown in offshore farms, and the utilisation of a rare Amazonian fungus which produces simple hydrocarbons that could be used to generate a new kind of fuel called ‘mycodiesel’.

If investments into sustainable third generation biofuels continue, then they may well be an ideal solution to dwindling fossil fuel supplies. One thing’s for sure, we can’t go on destroying rainforests and harming third world populations so that we can squeeze a bit of fuel from a bit of corn. What a joke. But there is potential for third generation biofuels, and perhaps one day people will remember the time when pond scum came to the rescue.


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