Biomass biological conversions are like having an aquarium. It is technically an ecosystem, so you have to consider all the angles and how things will get along. You have to keep everything alive by feeding it and making sure the conditions are correct, and most importantly you have to keep it wet. Living things don’t do dry well, so biological conversions range from wet to completely submerged, like your aquarium, water is a must.
Of the biological conversions available to us, arguably fermentation is used the most for chemicals production. Fermentation is generally the act of feeding microbes in a low O2 environment so that they will start producing things we want. A lot of microbes can live in O2 rich or O2 lean environments, but they produce very different things depending on what they are living in and when its a low O2 environment, they start using fermentation pathways. Fermentations can produce a very wide range of products from an even wider range of microbes.
It is important that you think about fermentation as a continuum because you may find that a lot of things seem to be fermentations and this can make it clearer. An easy way to think about it is apple juice. When you ferment apple juice microbes eat the easy sugar and make alcohols, acids, and tough sugars. If the microbe you used was yeast and you stop here, you have a nice hard cider. If you let it go a little longer, the microbe ecology changes and you become bacterial and acetogenic. Acetogenic bacteria are very very effective at eating everything marginally edible and will consume all the alcohols, acids, and tough sugars from the alcohol step. They combine these with CO2 and they generate acetates and acids, largely acetic and propionic. So, the gist of it is if you let the hard cider ferment a little longer, you end up with apple cider vinegar. Now, while we generally stop here from a food perspective, we don't have to and the final step is methanogenesis. Methanogens hate O2 and love acetic acid, it is their preferred food. So if I spike my apple cider vinegar with some aged compost and wait a few days I will make an anaerobic digestor and it will start to produce methane. So think of fermentations as a continuum; easy sugar turns to hard cider, hard cider turns to vinegar, and vinegar turns to methane.
It is imperative that we remember when we use biological conversions that living things do not exist to produce things for us. They can produce things for us if we feed them and provide a healthy environment, but they exist to replicate not to make chemicals. We find chemicals in and around certain living things, but they are by no means an engineered process like chemical and thermal conversions.
If you are interested in receiving the written slide notes for each lecture, please contact the USDA supported Advanced Hardwood Biofuels Northwest project at; [email protected]
An associated online E-campus course is also offered at Oregon State University; ecampus.oregonstate.edu/soc/ecatalog/ecoursedetail.htm?subject=BRR&coursenumber=350&termcode=all
Advanced Hardwood Biofuels Northwest is supported by Agriculture and Food Research Initiative (AFRI) Competitive Grant no. 2011-68005-30407 from the USDA National Institute of Food and Agriculture (NIFA)
This series contains 25 short lectures, each between 10 and 15 minutes long. The content in these lectures is flexible and can be used in a variety of ways to communicate bioenergy concepts to audiences from diverse backgrounds. An important objective of this series is to present facts about bioenergy and biofuels, and use them to explore misconceptions.