Since oil-derived fuels contribute to global warming and are not sustainable, people are looking to renewable biofuels to replace them. Bioethanol from sugarcane, the most widely used transport fuel and biodiesel from oil crops are being produced in large amounts, but will not be able to realistically meet the high demand.
The United States, for example, would consume nearly 530 million m3 of biodiesel annually, if all oil-derived transport fuel is to be replaced with biodiesel. To reach this level, sugar cane or oil crops would need to cover an area of approximately 111 million hectares, nearly 61% of all agricultural land in the United States.
This situation would look different if microalgae were used to produce biodiesel. In his article
Biodiesel from microalgae beats bioethanol, Dr. Yusuf Chisti from the School of Engineering, Massey University in New Zealand, explains why microalgae should become as competitive as diesel and how this could be achieved.
"Microalgae are photosynthetic microorganisms that convert sunlight, water and carbon dioxide to algal biomass and many of them are exceedingly rich in oil," Dr. Chisti told Checkbiotech. To convert the microalgal oil to biodiesel, existing technologies can be used.
Dr. Chisti evaluated many potential sources of biodiesel ranging from animal fat and several plant oils to oil from non-photosynthetic microorganisms. "None of them come close to microalgae in being realistic production vehicles for biodiesel," Dr. Chisti told Checkbiotech.
The extreme rapid growth of microalgae and the fact that they double their biomass within a few hours gives them a significant advantage over other oil crops.
But what does an algae plantation look like? How and where do these algae grow? Dr. Chisti has the answers to these questions. Algal biomass can be grown in glass tubes, called photobioreactors. To make use of the sunlight, these straight tubes normally are made of transparent plastic and are arranged like a fence with the orientation North-South. The diameter is generally less than 0.1m; the length depends on several factors, such as the concentration of the biomass, the light intensity, the flow rate and the concentration of the oxygen.
All tubes are connected to a degassing column, where adjustments of oxygen, carbon dioxide, temperature and pH can be made. Through these tubes pumps the nutrient-rich broth for the algae. The tubes also allow for ample sunlight to be absorbed by the algae.
As the algae flows through the tubes in the broth, a certain amount of the broth is harvested to process and the equal amount of fresh medium (normally seawater enriched with nutrients) is fed to the system.
The process to produce microalgal oil for biodiesel would yield many side products (e.g. water, biogas and carbon dioxide) which could be used within the process or as animal feed or fertilizer.
"A photobioreactor-based production facility would require about 5% of the agricultural land in the United States, for example, to meet all that country`s demand for transport fuels," concludes Dr. Christi based on his calculations. "Photobioreactors are currently used for producing microalgae for aquaculture and other high-value products."
Microalgae are a promising alternative to oil-derived fuels. However, various issues and economic factors need to be overcome and assessed. To increase the productivity of the algae, researchers will need to employ metabolic and genetic engineering changes to enhance their growth and fuel production potential.
Explaining the importance of biofuel from algae, Dr. Chisti told Checkbiotech, "At the moment barely any biodiesel is being made from microalgae and it could take more than 100 years to totally replace oil with renewable biofuels."
Fabienne Heimgartner is a Senior Science Journalist for Checkbiotech. Contact her at f_heimgartner@yahoo.de References:
Chisti Y. Biodiesel from microalgae beats bioethanol, Trends in Biotechnology (2008) Vol.26(3) p:126-131
CONTACT: Yusuf Chisti
Professor of Biochemical Engineering
School of Engineering, PN 456
Massey University
Private Bag 11 222
Palmerston North
New Zealand 4442
Telephone: +64-6-350 5934
Fax: +64-6-350-5604
E-mail:
Y.Chisti@massey.ac.nz© Checkbiotech
