Meera - You're listening to a special edition of the Naked Scientists with me, Meera Senthilingham. This week, we're exploring the role and production of hydrogen in the race to find green sources of energy. We've heard so far about the many roles bacteria can play in converting various organic sources of waste such as food waste into hydrogen for use thereafter in hydrogen fuel cells. But whilst the use of bacteria shows high efficiency in breaking down simple organic waste, like sugars, the ultimate aim is to tackle more complex forms of waste as well in order to produce the maximum amount of hydrogen possible and from a greater diversity of currently unused resources. But therefore, this is also where the process becomes more complicated as Lynne Macaskie explains.
Lynne - If we go to a more complicated waste like an agricultural waste then that's more likely to be starch or cellulose, and that presents some problems because many microbes actually don't like starch or cellulose. They prefer sugar. So, often what you can do is treat the starch or cellulose beforehand to make sugar or you can actually have mixed cultures. You can use microbes that act at high temperatures for example, or use a chemical system beforehand to break down the cellulose.
Meera - Chemical processes are the main focus at the moment, not only for waste containing cellulose but also lignin found commonly in wood waste as these compounds are also more complex. Too complex in fact, the bacteria which are much better suited to metabolising simple sugars.
Lynne - The microbial routes, it's very eco-friendly, but it's a bit restrictive because breaking down for example lignin, the component of wood, is still very problematic because it's quite hard to break this down biochemically. It's very slow. So, chemical processing comes into its own when you have recalcitrant - that's difficult - materials. And often, the only convenient way to treat these is to use gasification which is basically thermochemical treatment to just completely convert the raw material into gasses.
Meera - So, I guess at the moment, it's perhaps the chemical process that's more accessible or more feasible.
Lynne - At the moment, chemical processing is the main contender, but I see a future for biotechnology. In fact, I see a future in hybridising the two technologies together so that biotechnology can look at a fraction of the waste and chemical processing can look at the fraction which bacteria may find it harder to look at. So, it's horses for courses really. I mean, each waste is going to be completely different. A chocolate waste is very easy to treat biologically. Wood waste is not. And really, that's the cutting edge of this area at the moment - how do we treat very difficult waste?