Chemical products from green waste


Your keyboard, the steering wheel of your car, the tires of your bicycle ... Nowadays, we produce all our chemical resources for plastics from fossil oil and natural gas. These sources are non-renewable and their exploitation has a large environmental impact. But an alternative exists. Scientists discovered bacteria capable of converting green waste into useful, chemical building blocks. An example: biobutanol. Biobutanol is an important product to make rubber or paint.

The hero of this story: a bacterium from the Clostridium family. [1]These bacteria eat the sugars present in the green waste and produce biobutanol. As a waste source, almost anything can be used. My favorite: the Scottish company Celctic Renewables is using biomass waste from the whisky industry as a feedstock. The waste is first pretreated and cooked, to extract a maximum amount of sugars. Besides biobutanol, two useful side products are also produced: acetone and ethanol.

Unfortunately, our bacteria stop growing after a while. Butanol, in high concentrations, is toxic for our favorite tiny microbes. The same happens when you make beer or wine: at too high alcohol levels, the yeast dies off.

The premature death of our clostridial bacteria is a huge problem. You want to convert as much sugar as possible into biobutanol. Secondly, biobutanol must be removed from this mixture of waste and bacteria. The lower the butanol concentration, the more difficult this becomes. It is like finding your car in a huge parking garage: the more cars are parked there, the more difficult it becomes to find exactly yours.

To convert more sugars into biobutanol, we can use a small trick. The bacteria present in the waste are in a huge vessel. If you only fill this vessel for a tiny amount, the bacteria will be able to convert his tiny amount of waste. When the amount butanol becomes too large, you just add a little bit more waste. The butanol present in the vessel will be diluted and the bacteria will be able to further convert the waste. This way, you convert more sugars, than when you would fill the vessel completely.

You could also try to make the microbe more resistant to biobutanol. Scientists use two methods for this. In a first method, you bring the bacteria into contact with ever increasing butanol concentrations. Bacteria who are more resistant will survive and will be selected. It is in fact an artificial way to perform natural selection. In a second method, you try to use novel genetic techniques to adjust the DNA of the bacteria. In this way, you can make new microbes, who are more resistant or who convert more sugars.

But such techniques also have their limitations. Scientists fail to successfully make microbes who resist to biobutanol in sufficiently large quantities.

To purify biobutanol from mixtures of waste and bacteria thus remains a huge challenge. Do you want to know more? Check out the other posts!

[1] Fun fact: other species from this family make botox!