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How Green are Biofuels?

Posted by Alex Barrett on 22 March 2017 at 5:15 pm

Our society is addicted to oil. The International Energy Agency estimates that the world will use 96 million barrels of oil (152 billion litres) a day throughout 2016 [1]. Our oil usage shows no sign of slowing down, so we desperately need an alternative for this non-renewable resource.  

So can we make fuel in a carbon neutral manner? Biofuels are often heralded as a sustainable alternative to fossil fuels. But how sustainable are they really? Can we meet our energy needs with carbon neutral fuel? Or do the other environmental impacts of biofuel production outweigh the benefits?

Biofuels are produced by cultivating oil rich plants which can then be refined into a fuel. Because these organisms trap carbon dioxide when they photosynthesise, this technology has the potential to be carbon neutral. The carbon which goes into the atmosphere when we burning the resulting fuel was taken out as the plant was growing. Various fuel crops can be grown in different parts of the world [2].

Challenges

Unfortunately biofuel production is not as sustainable as it first appears.

Fuel demand is vast, and so the area that would need to be farmed in order to supply this with biofuels is also colossal. There is a limit to how much cultivated land we can, and should use for biofuel production, as we also need to grow enough food crops for an ever increasing population as well.

The other alternative is to clear new land for farming, but many of the most productive biofuel growing areas are in tropical countries like Brazil. Clearing land for biofuel production means cutting down vast swathes of rainforest. Replacing rainforest with fuel crops would result in far more carbon emissions than are saved by using biofuels rather than crude oil. Unfortunately this is precisely what is happening in many parts of the world.

If it is possible to meet our fuel needs with biofuels then they will have to be farmed intensively. Monoculture, intensively growing one crop over a large area, degrades the land requiring ever greater volumes of fertiliser.

Fertilisers are very useful, but they have a number of problems; it costs a lot of energy to produce fertilisers in large volumes, and they are made from non-renewable resources. Fertiliser use also increases the nitrous oxide emissions from microbes in the soil, contributing to the greenhouse effect [3]. It has been estimated that Brazilian ethanol production in 2006 released 436 kg of CO2 equivalent for every cubic metre of fuel produced [4].

Algal biofuels

Algae are aquatic, photosynthetic organisms, many of which produce oils. Algae don’t require farmland. They can be grown in tanks or ponds, potentially in desert environments that would be unsuitable for conventional farming [5]. This is a major advantage over other fuel crops. Unfortunately algal biofuels have additional challenges [6].

The infrastructure required for the production of algal biofuel is much higher. Glass and metal are needed to build tanks and these are energy intensive to produce. Water availability is obviously vital, particularly in hot, dry areas. Algae can be grown in brackish or alkaline water, but would still put an additional stress on water use in regions that can least afford to waste it.

Algae would still require high concentrations of fertiliser. Care has to be taken that nitrogen rich water from algal farms is not reintroduced to the environment, where it could cause severe damage to ecosystems.

Producers of biofuels are confident that they can rise to these challenges and one day produce clean and carbon neutral fuel. But it is possible that biofuels will never be able to supply our energy needs in an environmentally friendly manner. The best way to build a more sustainable world is to reduce the amount of fuel we need, rather than looking for new sources of it.

References

  1. International Energy Agency
  2. Grist
  3. Science News
  4. C Macedo, I. C., Seabra, J. E. A., & Silva, J. E. A. R. (2008). Green house gases emissions in the production and use of ethanol from sugarcane in Brazil: The 2005/2006 averages and a prediction for 2020. Biomass and Bioenergy, 32(7), 582–595.
  5. CNBC
  6. Hannon, M., Gimpel, J., Tran, M., Rasala, B., & Mayfield, S. (2010). Biofuels from algae: challenges and potential. Biofuels, 1(5), 763–784.

Image Credit: Algae on a water tank, Alex Quinn via flickr

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