New Biofuel Research - Watermelon Bioethanol Production

We’re all aware that the world faces an energy crisis. Our reserves of fossil fuels (coal, oil and natural gas) are running low because we’re using them much faster than the Earth can replenish them – and burning them contributes to atmospheric pollution and global warming to boot. Finding ways of making renewable and more environmentally friendly energy sources usable, sustainable and economically viable is a challenge faced by governments worldwide. While solar power and wind generated electricity are usually the first things that people think of when asked to name a renewable energy source, it is biofuel that is currently the subject of much research and development since their use requires less modification to our current infrastructure than other sources.

Our current fuels of choice are all derived from oil, coal and natural gas. These materials contain a large amount of stored energy in the form of carbon bonds from multimillion-year old skeletons of animals and plants, decayed and compressed under pressure. Since fossil fuels took millions of years to form, they are not quickly regenerated and this is where our problem lies. Aside from the fact that we’re running out of them, we’re also releasing millions of years-worth of stored carbon in the form of carbon dioxide (CO₂) that our photosynthetic organisms cannot recycle quickly enough to maintain stasis.

New energy sources  

Biofuels however, are fuels which are produced from sustainable materials, such as crop plants and organic waste. Although biofuels still need to be burnt to release their energy to drive our cars and work our power stations, the exhausts that they emit contain less harmful impurities and the CO₂ that they release is only as old as the plants themselves. Therefore, by increasing biofuel use, we can significantly reduce our overall carbon footprint. By maintaining sustainable biofuel production, or even better, by using waste that would otherwise be land filled or burnt in an unhelpful way, we can help to keep CO₂ levels in balance.

Buses running on 85% bioethanol made from fermented wheat by-products or “veggie vans” that use biodiesel as their fuel of choice are gradually becoming more common on the UK’s streets. In the UK, most bioethanol is manufactured by fermenting surplus wheat that farmers are unable to sell to flour producers or breweries, and biodiesel often comes from excess rapeseed oil stocks. Clearly, not every country or region around the world has the same staple crops and so current research into the viability of other crops or waste products is being carried out so that feedstock type or availability or does not limit the progress of biofuel use. In Brazil, the world’s largest user of bioethanol, the main ingredient for the national cocktail caipirinha, also doubles as the source of biomass for their bioethanol production needs. In other parts of South America, maize has been successfully used to produce fuel. Other countries however, have started to think outside the box…

Bioethanol production from watermelons

Researchers at the South Central Agricultural Research Laboratory in the USA published an article in August 2009 claiming that watermelons may be an important and previously untapped source of feedstock for bioethanol production⁽¹⁾. 44 of the 52 states in the USA grow watermelons commercially and yet because of our penchant for perfectly shaped melons, 20% of this crop is left to decompose in the fields and is wasted each year. In addition, a significant proportion of the watermelons that are sold commercially – somewhat surprisingly – go to pharmaceutical companies who extract the compounds lycopene and L-citrulline that are then incorporated into drugs for treating prostate disorders and high blood pressure. This generates even more organic waste that researchers now propose could be put to use towards more environmentally-friendly fuels. By combining concentrated watermelon juice with yeast and fermenting under controlled conditions, Wayne Fish and colleagues estimate that the 8.4 tons per hectare of surplus melons could produce as much as 200 litres per hectare of bioethanol.

Bio-oil production from waste furniture

Also utilising an unusual source for the production of biofuel is South Korea who, rather than using excess or waste crops, are turning to waste furniture for their biomass needs⁽²⁾. An estimated 2.4 million tons of tables, wardrobes and other wooden furniture items were land filled in Korea between 2005 and 2008 and, so say researchers collaborating between several Korean universities, this waste wood could be better put to use in the process to produce bio-oil. By heating wood chippings to temperatures of 450ºC in the absence of oxygen (during a process known as pyrolysis), biomass material can be condensed into a high-energy content oil that can be burnt in order to generate electricity. What’s more, gases produced as a by-product of this process can be recycled and combusted to generate the high temperatures needed for the reactions to occur, thus the production of bio-oil (not to be confused with the ointment used to fade scars and pregnancy stretch marks!) can be completely self-sustaining.

Biofuels from genetically modified plants 

A third and more controversial area of research, recently reviewed by collaborators at several Californian institutions, has suggested that genetically modified plants may one day be important for the production of biofuels⁽³⁾. Since the genomes of several important and common bioethanol feedstock crops are now known, genetic modification of other crops to incorporate required characteristics for ethanol production may be possible. Lignin, for example, is a compound found in plant cell walls that contains a high concentration of starch. Starch, in turn, is made up of units of sugar, which drives the fermentation process. If high lignin content could be genetically transferred to crop plants which do not normally have such a high potential for bioethanol production, then even more otherwise wasted crop resources could be utilised for our energy needs. As always, genetic modification remains a touchy subject and is certainly one that needs further research and testing if it is to be viable.

While 100% of petrol stations in Brazil now sell biofuels, progress in the UK is relatively slow. To be able to use bioethanol, vehicles must be specially modified so as to prevent engine damage and that, of course, costs money that in this dreaded time of “economic downturn” sees any investment of this kind, both by companies and individuals alike, way down the list of priorities. A growing number of companies do now use bioethanol for their fleet vehicles, and a small but growing number of hybrid cars for personal use do now exist, but our infrastructure must change radically if we are to see the use of biofuels really take off.

⁽¹⁾ Fish, Bruton and Russo, Watermelon juice: a promising feedstock supplement, diluent and nitrogen supplement for ethanol biofuel production, Biotechnology for Biofuels 2: 18, 2009 

⁽²⁾ Heo et al., Bio-oil production from fast pyrolysis of waste furniture sawdust in a fluidized bed, Bioresource Technology 101: 1, supplement 1, 2010

⁽³⁾ Simmons, Loque and Blanch, Next-generation biomass feedstocks for biofuel production, Genome Biology 9: 242, 2008 

Published - Wed 18th Nov 2009 10:21:28