Being a high yielding, non-food crop and relatively high carbohydrate composition makes Arundo donax (giant reed) a noteworthy feedstock for producing bioethanol. The feasibility of Arundo donax for bioethanol production was assessed by the University of Washington via pre-treatment, enzymatic hydrolysis, and fermentation. See the results below!
Producing bioethanol through Pre-treatment, aka steam explosion
Giant reed (the whole plant, including leaves) was chipped to about 3cm x 2cm x 0.5cm pieces, and the biomass was kept at 4 Celsius degrees.
Severity was measured using the severity factor called Ro, which links the effects of time (min) and temperature (°C) of the pre-treatment. The pre-treatment severity for giant reed ranged from Ro 3.4 to 4.2 (see below).
Preceding the steam explosion, giant reed was saturated with gaseous sulphur dioxide in the amount shown below by adding SO2 to plastic bags with 300 g (oven dried weight) of biomass. The bags were weighed and left at room temperature overnight. Then the biomass was added to a reactor of a 2-L Stake Tech II steam gun (Stake Technologies; Norvall, ON, Canada) in 50 g aliquots.
The samples were pre-treated at the temperature and time shown below. After the specified reaction time had passed for each portion of biomass, a pneumatic valve was opened, blowing the pre-treated slurry into the collection vessel. The water soluble fraction (WSF) was separated from water insoluble fraction (WIF) using vacuum filtration. The WIF was then washed with a volume of water equivalent to 20 times the dry weight of the sample.
Producing bioethanol through Enzymatic hydrolysis
This part of the experiment was carried it out in 125 mL Erlenmeyer flasks in triples, with the total solution volume being 50 mL.
The washed water insoluble fraction solids were diluted to 2% consistency with acetate buffer (50 mM, pH 4.8) at 50°C and agitated at 150 rpm in an orbital shaker. Enzymes were added in the form of cellulase at 20 filter paper units.
The 500 μL samples were taken periodically over 48 hours, boiled for 5 minutes and stored at -20°C.
https://arundobioenergy.com/cellulose-based-bioethanol-from-arundo-donax/
Producing bioethanol through Fermentation
Fermentation of the liquid water soluble fractions (WSF) was conducted in 125 mL flasks containing 50 mL medium pre-adjusted to pH 6.0 with 0.5 M sodium hydroxide and injected with 5 g/L of S. cerevisiae. Ammonium phosphate (2 g/L), sodium phosphate (0.2 g/L), and sodium nitrate (2 g/L) were added to each flask.
The fermentation vessels were maintained at 30°C with continuous orbital agitation (150 rpm). Samples (0.5 mL) were withdrawn aseptically by a syringe, centrifuged for five minutes at 15000 × g and 4°C, and the supernatant fluid was filtered by using a 0.22 μm syringe filter) and then stored at -20°C until analysis. Sugars and ethanol were determined periodically from the aliquot culture samples during the fermentation.
Simultaneous saccharification and fermentation (SSF) experiments were also performed under nonsterile conditions in 125 mL flasks, with S. cerevisiae strain ATCC 96581being the sugar fermenting microorganism. The water washed, water insoluble fractions (WIS) at 8% concentrations were supplemented with the water soluble streams (WS) during SSF experiments. The fermentation vessels were maintained at 37°C with continuous agitation (200 rpm).
Each experiment was run in three times.
Results
Simultaneous saccharification and fermentation (SSF) of the combined water insoluble and water soluble fractions from steam pre-treated giant reed at severity condition of 190°C, 5 minutes and 3% SO2provided the highest ethanol yield − 79% of the theoretical maximum, which corresponds to 0.179 L ethanol/kg of raw material, which equals 179 litres/tonne. It must be mentioned, though, that this number applies to an experiment carried out in a laboratory. In ideal field conditions, Arundo donax has the capacity to produce up to 300-330 litres/tonne of cellulose ethanol.
Overall, Arundo has prevailed as one of the most competitive resource for bioethanol, not only because of its high cellulose content but also for its high biomass yielding per hectare.
If you have any questions regarding methods of producing bioethanol or specifically the capability of Arundo as a feedstock, visit our website or send us an email at info@arundobioenergy.com
