Process turning waste to biofuels works on paper
19th July 2013
Researchers from the Institute of Food Research have successfully produced bioethanol from waste paper, as part of efforts to turn waste into valuable products.
To increase their sustainability, there is currently a drive to turn away from deriving biofuels from food crops, such as corn and sugarcane. Bioethanol derived from waste streams from agriculture and the food chain is more attractive as this avoids competition with food crops, reduces food waste and lowers the carbon footprint. Achieving this on a commercial scale needs to overcome a number of hurdles, and the Biorefinery Centre on the Norwich Research Park is looking to overcome these.
Sugars are the starting point for the production of bioethanol, and are readily obtainable in large quantities from food crops such as sugar beet, corn and wheat. In agri-food waste streams however, the sugars are effectively locked away in the structure of the plant material – mostly in the form of lignocellulose. Lignocellulose gives plant cells walls their rigidity and resistance, but this makes them harder to convert into biofuels. For most agri-food waste streams, a pre-treatment is needed to break open these structures, reducing the overall economic viability of the process.
One common waste stream doesn’t suffer from this problem. Waste paper, particularly shredded paper that cannot be recycled, has effectively been pre-treated, with much of the lignocellulosic structure broken down. Now researchers at IFR, which is strategically supported by BBSRC, have for the first time produced high concentrations of bioethanol from waste paper that match the yields obtained from first generation biofuels.
Achieving this saw the team overcome a number of obstacles. Paper absorbs water and becomes difficult to mix. A specialised pilot bioreactor able to mix the material needed to be used. Adding the paper in batches also allowed digestion to occur, preventing the material from becoming too thick.
Ethanol conversion is a two-step process. Enzymes are used to break down the complex carbohydrates (saccharification) to simple sugars that yeast ferments into ethanol. Semi-simultaneous saccharification and fermentation was used. After an initial enzyme treatment, further saccharification feeds sugars into yeast fermentation simultaneously. This, along with the mixing and the batch addition of paper waste keeps the bioreactor working steadily and a final ethanol yield of 11.6% – as high as that in current commercial biofuel production and higher than any other reported yields from paper or paper pulp waste streams..
The researchers believe that there is considerable room to improve on this figure even more, by optimising batch addition regimes and the initial enzyme concentrations (which are low to reduce input costs). Different yeast strains may convert sugars to ethanol more efficiently, for example heat-tolerant yeasts may be better suited the exact conditions in this set-up. The researchers are working with the National Collection of Yeast Cultures, a BBSRC-supported National Capability based at IFR, to investigate this.
These initial findings relate to pilot scale experiments, and to be viable the system must work on the industrial scale. Scaling up must be economically viable, taking into account things such as the energy needed for the crucial agitation of the paper material. However, with over 12 million tonnes of paper waste being generated annually in the UK alone, there is great potential to divert this into a new sustainable source of fuel or higher value chemicals.
This research was led by Dr Adam Elliston, as part of his PhD studentship under the supervision of Professor Keith Waldron at IFR. Adam’s PhD explored ways of exploiting different waste streams and turning them into biofuels and other valuable products.
This article is one of a series highlighting the work of IFR’s excellent PhD students who received their Doctorates at UEA’s congregation ceremony in July 2013.
High concentrations of cellulosic ethanol achieved by fed batch semi simultaneous saccharification and fermentation of waste-paper, Adam Elliston et al, Bioresource Technology doi: 10.1016/j.biortech.2013.01.084