Profitable, sustainable seaweed-sourced bio-ethanol edges closer
Seaweed has the potential to be a sustainable source of bio-ethanol, but compared to many other food and non-food sources, it is rather complicated to process.
Two AIC Associate Fellows, Dr Sulfahri (Hasanuddin University) and Dr Alexandra Langford (University of Queensland), with a team from those institutions plus RMIT University, have investigated two new methods for breaking down the tough cell walls of marine macroalgae, or seaweed. This is the vital pre-treatment stage before converting seaweed into bio-ethanol.
The pretreatments tested were the use of fungus and the use of ozone. ‘Ozonolysis’ has never been tested for this use before, while fungal treatments have been, but not across the entire production process. The results were promising in both cases.
Two types of red seaweed were used, Kappaphycus alvarezii and Gelidium amansii, which both grow fast and are rich in carbohydrates, a key ingredient in ethanol production. Another distinguishing quality is that unlike most other bio-ethanol sources, neither of them is an essential food crop nor one that takes land away from food production.
Indonesia produces over two-thirds of the world’s supply of red seaweed, almost entirely through small household industries. Currently, red seaweed is mainly exported for use in food (as a gelling agent) and in cosmetics, and farmers are vulnerable to price fluctuations. “Diversifying options for processing red seaweed domestically,” the ozone report states, “therefore promises benefits for poverty reduction in Indonesia” (Sulfahri et al., p1).
The Indonesian government is indeed focussed on increasing production and developing downstream processing in the sector.
Furthermore, development of seaweed-based bio-ethanol production in Indonesia is a logical direction to move in for environmental reasons and to reduce exposure to foreign oil markets. The government has mandated nationwide use of petrol with a 10 per cent bio-ethanol blend (E10) by this year, which former head of state-owned fuel company Pertamina, Karen Agustiawan, has said could reduce petrol imports by 30 million barrels a year.
Indonesia’s current go-to source for bio-ethanol, sugar cane, may not be sufficient for meeting this target. Could seaweed help? Perhaps not, unless affordability and sustainability of the conversion process is improved.
In short, bio-ethanol is produced by converting carbohydrates in organic material to glucose through hydrolysis, and the glucose is then fermented into ethanol.
Both these studies aimed to find alternative pre-treatments to break down cell walls in the target seaweed types, to allow access to the carbohydrates in the first place. It is known that the use of acid and other materials for this step produces harmful and costly by-products.
Researchers developed and tested a method for using the fungus Trichoderma harzianum as a pretreatment. This is a more organic approach than most alternatives, and was found suitable for various reasons:
- The enzymes it produces disrupt the algae cell wall (core task)
- its by-products do not inhibit the subsequent fermentation stage of production
- biomass produced during this pretreatment process can be used as a nutrient in the fermentation stage, potentially reducing input costs.
“The study demonstrates that fungal pretreatment prior to enzyme hydrolysis increased sugar yields 2.3 fold compared to untreated algae, and nutrient supplementation using the recovered fungal biomass increased ethanol yields by up to 38.23 per cent. This data suggests that the use of fungi for pretreatment and nutrient supplementation could greatly increase the economic viability of production of these third-generation biofuels.”
Acid and ozone pretreatments were compared across the pretreatment, hydrolysis, and fermentation stages of bioethanol production.
Acid pretreatment has several disadvantages, including high temperature (therefore more costly and complicated) reaction conditions and by-products that interfere with the fermentation process.
This study showed that although acid outperformed ozone over the pretreatment and hydrolysis stages, it also produced inhibitors to later stages of the process, reducing its overall efficiency enough for it to be outperformed by ozone.
“These results indicate the potential of ozonolysis as an economic and environmentally friendly pretreatment for the production of bioethanol from marine algae.”
Through the AIC’s Partnership for Australia-Indonesia Research (PAIR) Program, Dr Sulfahri and Dr Langford are part of an interdisciplinary team of researchers seeking to help South Sulawesi unlock the potential of it’s seaweed industry, to drive prosperity and development.
Image: DKP Provinsi Jawa Timur