Extracting oil from algae - Planet Earth
As a clean renewable source of energy, algae is great in theory. Not only does it take in CO2, but some species produce useful quantities of lipids or fats which can be converted into biofuels. But earth scientists have hit a snag, how do you actually extract these useful chemicals? Planet Earth podcast presenter Richard Hollingham met Microbial Ecologist Simon Thomas at the Plymouth Marine Laboratory.
Simon - We're in a constant temperature room at the moment, so this is actually set to 15°C and we're surrounded by bottles of algae growing gently in the light and also some larger volumes of algae. Here, we have 10 litres of various algae. So, we have a column as you can see which is bubbling air through it in front of a light source and that's very basic of what we do.
Richard - It looks like an oversized fluorescent tube full of this green liquid and it's bubbling from the bottom up to the top and that's a particular type of algae.
Simon - The one in there is actually Dunaliella Salina. It's of commercial interest because it produces beta-Carotene at certain stages of its life cycle. The bubbles are there to keep it moving but they are also there to help gas exchange, so it gets oxygen out and CO2 in.
Richard - And these, you described as photo bioreactors. So, what is a photo bioreactor?
Simon - It's the algal equivalent of a fermenter. So, in a fermenter, technology is very old and it grows commercial scale amounts of bacteria or yeast typically. These are an attempt to take that technology onto algae and it is to add a certain degree of control that is very hard to do in an open pond system.
Richard - And ultimately, you're looking at products from these, but you are looking at how to get those products out.
Simon - We are, yes. For any future development of biodiesel from algae, one of the most important thing is to try and get the product out, but also for the other applications of algae - pharmaceutical uses, cosmetic uses, you still need to get the product out of the cell. Typically, they're produced within a cell and breaking the cell open is very difficult with algae. They're very resistant to stress. So, we're trying to find some novel ways of breaking them apart. One of the ways we're looking at is using viruses that infect the algae and they naturally break the cells apart. We're looking at novel mixing technologies which use things like beads impregnated metals and enzymes from bacteria that would naturally break apart algae. So, we're very much going back to nature in order to find a way of trying to solve this problem. It's quite tricky and it is taking an awful lot of time and an awful lot of people are looking at this at the moment. We have had some success.
Richard - And if you imagine an individual microscopic algal cell, so that's a single plant cell effectively. How much of that is oil and how much oil can you breed for it to produce?
Simon - Normally, you would say something like 10% to 15% would be oil but we've developed some strains of algae that produce up to 40% lipids and what we're trying to do is, normally, they would only accumulate these lipids late on in their life cycle. And we're trying to get them to actually produce this oil early on whilst they're actively growing, but of course, there will always be a balance between growth and storage material so we're trying to solve that particular conundrum.
Richard - So, you've got one of these columns just under 2 meters high, full of algae. A sizeable percentage of that is lipid, is potentially oil, but the getting out is the challenge.
Simon - Well, the scary thing and one of these columns here would only be about 1 gram of oil.
Richard - Okay.
Simon - So, one of the challenges for the future is actually scaling up these systems to meet the massive demand there would be, but even in a very good system, in 10 litres, you'll be lucky if you've got more than 2 or 3 grams of oil. So, you need to come up with a very large solution or maybe find a way to grow even denser, which again, is something we're looking at.
Richard - Now, if we came out of this room, into the main laboratory here, you have scaled this up. So, this is fairly big room And at its centre is almost another room which is full of these tubes running horizontally rather than vertically.
Simon - Basically, you split the volume of the tube into a manifold and the idea is trying to maximise the amount of light the algae gets whilst minimising the amount of time they've spent before the oxygen is removed. So, when oxygen gets too high for a photosynthetic organism, it becomes toxic. It is a balance between exposure to light and the amount of CO2 they take up and the amount of oxygen they produce. So, this has been designed in collaboration with a big engineering firm and we worked out the formula based on their experimental design and we've come up with this particular design.
Richard - Is that continuously replenishing or is it the algae sort of sitting there and doing its thing?
Simon - The algae just flow through the tubes and the idea is you get turbulent flow within the tubes so the algae actually go from the middle to the outside and it maximises their exposure to light and it also maximises their ability to get rid of the unwanted gases and take up CO2.