Biorefineries
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Overview
Biorefineries are away of using biomass as the source material for all kinds of chemical substances and feedstocks to chemical industries. They are a way of utilising the (hard) parts of plants that today go unused and turn them to valuable products. At the same time they are a way of bind carbon from the atmosphere to these products thus reducing climate change.
Sugars in the biomass can be fermented with the help of specific microorganism to as example to ethanol or biodiesel. In general, the concept of converting biomass into a variety of products like biofuels and chemicals is called biorefining. There are many different types of biorefineries but in general the process involves steps like chopping and grinding the material into small pieces to sped up the process. After initial grinding in pre-treatment heat, chemicals and mechanical grinding are used to break down the structure of the biomass. Next comes the actual conversion process where a specific microorganism is used to for example ferment the created broth of biomass. Also hydrolysis (breaking down the structure of molecules by adding water) can be used. Next comes separation by methods such as distillation, filtration or centrifugation. The separated liquid needs to still be purified with for example by distillation, crystallization or filtration. Last step is product recovery.
In addition to biofuels like ethanol and biodiesel, biorefineries can be used to produce chemicals like lactic acid and xylitol or materials like bioplastics and biocomposites.
They can also produce co-products like animal feed or fertilisers.
Not all biorefineries work on the principle of fermentation. As example are ones using PHAs. Polyhydroxyalkanoates (PHAs) are structurally diverse microbial polyesters synthesised by many different bacteria. Certain microorganisms store PHA in cells as reserve of carbon and energy.
Features of the simplest PHA – Polyhydrobutyrate (PHB), are similar to polypropylene and polyethylene. This makes PHAs as a substitute for oil based plastics. One of the benefits of PHAs is that microorganisms produce PHAs but can also degrade them again, making them biodegradable,
PHA using biorefineries can use a variety of inputs like leaves from existing plants (for example sugar beet leaves or unused parts of other plants grown as food), but also various waste streams like sludge from waste water treatment plants, industrial waste waters from food, paper or chemical industries, even municipal solid waste.
PHAs are extracted from when microbes after they have processed the feedstocks and processing continues to turn them into biofuels, consumer, agricultural and horticultural products, catering and packaging materials, coatings and rubbers, pharmaceutical and medical products as examples
Currently the cost of production of PHAs is still too high. There are production process difficulties in making the right composition and quality of PHAs in fermenters and the growth medium for bacteria is high, and the extraction and downstream processing add to costs. But with time (like with any technology), prices are expected to come down.
As a summary, niorefineries are a different path to decentralise production of chemicals, food, animal feed and energy and would require much longer own treatment on their own.
As a good summary of various biorefinery options in a small-scale (read decentralised) setup, take a look at this overview.
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