Sourcing Hydrogen from Biomass
Meera - This is where the work of the biosciences and chemical engineering departments at the University of Birmingham comes in. Researcher Mark Redwood is working on obtaining hydrogen gas from a natural and widely available source: biomass, obtained from organic waste.
Mark - The thing about organic waste is it's really diverse. It's all sorts of different things. For example, there's the caterings wastes, the plate scrapings that come off the plates in kitchens and after the whole BSE problem, you can no longer feed that back to animals because you might accidentally feed pork back to a pig. So nowadays, there's a lot of regulations and difficulties with disposing of all sorts of kinds of wastes. There are things like apple pomace, or spent grain that comes out of brewing, just excess food that doesn't get eaten or go spoils in the supermarkets. Altogether, there's over 100 million tons of suitable biodegradable wastes every year just in the UK.
Meera - And so, how would you set about turning this into hydrogen?
Mark - We would build what we call an integrated biohydrogen refinery where we'd use a diverse range of techniques to squeeze any sort of organic wastes or biomass into different fractions. And then ultimately, all of those get put into a bioreactor using special bacteria of different types to turn the waste into hydrogen. It's about using the calories, using the food value in all different sorts of wastes to make the bacteria grow and to produce hydrogen. And then there are special ones that also use sunlight for an extra boost.
Meera - And so, what's the actual process? So what is it in the food waste that's then converted into hydrogen and what else do you get as a by-product?
Mark - Well, in any form of bio waste, it's the same feedstocks that give us food value when we eat food. It's the carbohydrates, the proteins, the fats, all those things are suitable for bacteria to breakdown and grow, and make into hydrogen. Now, what we do is we start off with something that's quite sugary. First thing we do is put it into a fermentation which is like what happens when yeast works in brewing where you use E. coli bacteria or other bacteria in a dark fermentation, break down the sugars and produce hydrogen and carbon dioxide, and a bit of bacterial growth.
Meera - And when you say dark fermentation, you basically just mean without light.
Mark - Yeah, just without light.
Meera - And fellow scientist Rafael Orozco is leading the work using bacteria in this dark fermentation process.
Rafael - There is a range of bacteria that can do the job, converting the sugars to hydrogen. We used facultative anaerobes, so just E. coli, in different strains of E. coli because these are very easy strain to work with. It's easy to grow and the fermentation conditions are mild. For experiment purposes, it's a very, very useful microorganism.
Meera - And what does this E. coli work on? So it takes sugars and what does it do to then somehow get hydrogen and other by-products from it?
Rafael - It converts sugars to hydrogen and a mixture of organic acids, following a specific metabolic pathway.
Meera - And how efficient is that process then? So, for all of the sugars coming in, how much hydrogen do you get out from this initial use of bacteria like E. coli?
Rafael - Well in this case, the maximum yield will be like 2 moles of hydrogen per mole glucose through the development of our fermentation techniques and culture media and conditions, we have achieved continuous fermentation with 80% of that maximum potential.
Meera - Whilst this dark fermentation is showing good yields of hydrogen, the team are now further improving on the efficiency of this process by using the organic acids released when their E. coli bacteria breakdown these sugars. Mark Redwood again.
Mark - Now, the dark fermentation also produces organic acids. These are things like vinegar or butyrate. These organic acids are the preferred foods for photosynthetic bacteria, purple bacteria that use sunlight to convert the waste product of dark fermentation into hydrogen. And actually, if you took all of those organic acids from a dark fermentation and put them into the photo fermentation using sunlight, you'd get about 5 to 10 times as much hydrogen from the photo fermentation as you got from the dark fermentation.
Meera - So, how do you focus in your research in this area? So you've shown that it can produce so much more hydrogen. So what do you actually look into to make this happen on a larger scale?
Mark - Well, at the moment, we're developing reactors that can be used to take the technology out from the lab into the real world and a big part of that is that these reactors will have to be very large because sunlight itself is not that intense. So, in order to get a lot of sunlight energy, you have to cover a lot of space. And we've come up with one solution to that problem and which is what we call dichroic beam sharing and it uses a really well-known bit of technology called the dichroic mirror. So, I've got one of them here and that's why we're outside in the sunlight. And we've got a little 2 inch across circular mirror. It's just a normal piece of glass which has on it an organic coating which is a dichroic coating and that interacts with the sunlight and it splits it. So, some of the wavelengths, some of the colours get transmitted and some of the colours get reflected. This is actually really useful because those colours can be fed to different organisms making different biofuels because some organisms like to use red light and some organisms like to use other colours of light. Then it happens to be that the purple bacteria that are really good at using organic acids work really well on the reflected light and other things - like algae, green things, higher plants, grass, crops - those work really well on the transmitted light which is mostly red. So, that means if we could use this dichroic mirror to split sunlight, we can drive 2 bioreactors in the same space and effectively double the amount of biofuel it can produce without needing anymore land.
Meera - So this is very much a multistep process, bringing different biological processes together. That was Mark Redwood from the University of Birmingham.