TRANSFORMATION OF CASSAVA TO BIOETHANOL

FACT SHEET

Cassava in Asia is predominantly used for producing starch or chips for animal feed. Unlike African nations, it

is not often used for human consumption due to it containing toxins. Thus cassava becomes a suitable candi-

date for alternative vehicle fuels such as bioethanol. Research teams from King Mongkut’s University of Tech-nology Thonburi (KMUTT) and the BIOTEC Cassava Starch Technology Research Laboratory have been working

together for a number of years to improve the fermentation processes involved in producing bioethanol from cassava. Thailand is now a world leader in this technology and has teamed up with the United Nations Indus-

trial Development Organisation (UNIDO) to transfer this knowledge to other cassava producers in ASEAN.

With support from the Global Environment Fund (GEF), a project entitled Overcoming Policy, Market and

Technological Barriers to Support Technological Innovation and South-South Technology Transfer:

the Pilot Case of Ethanol Production from Cassava has been formulated to assist in making technology

developed in Thailand available to neighbouring countries.

The project involves a large training component, including demonstration at KMUTT’s pilot plant and is target-

ed primarily at the private sector in ASEAN. The training package includes improved productivity of cassava

root production, improved in-factory raw material management and improved fermentation process. This

latter applies High Gravity/Very High Gravity Simultaneous Saccharification and Fermentation, or VHG-

SSF technology, giving much improved performance and yield.

Conventional Process for Transformation of Cassava to Bioethanol

The conventional process for transformation of cassava to bioethanol starts with cassava cultivation.

Thailand’s cassava cultivation area varies between 6 and 7 million rai with an annual production of 20 million

tons

ASEAN Centre for Cassava

Research & Development

http://www.aseancassava.info

Email: aseantapioca@gmail.com

Cassava Starch Technology Research Laboratory

ASEAN Centre for Cassava Research & Development

Conventional Process for Transforming Cassava to Bioethanol.

or productivity of 3 tons per rai (19 tons per hectare) on average. The normal practice is for farmers transport harvested cassava roots to the cassava chip processing plant. At the cassava chip factory, cassava roots are chopped to smaller pieces and sun-dried before being kept in a storage warehouse. The chips

are then transported to the ethanol factory. These chips are milled, sieved to fine pieces and water is added during this step. The slurry is then cooked to facil-itate disruption of the ordered structure of starch granules making them more susceptible to enzyme hydrolysis. During ethanol production from cassava,

starch accumulated in the roots are converted to sugars, either by acid or enzymes prior to sugar fermentation by yeasts. The two-stage hydrolysis by en-

zymes – liquefaction and saccharification – yields glucose for the latter fermentation process by yeast. At this point, the saccharifying enzymes and yeasts can work under the same conditions, therefore, these two steps, i.e. saccharification and fermentation, can be performed at the same time – a process called Sim-

ultaneous Saccharification and Fermentation (SSF). The typical concentration of ethanol at the final stage of fermentation is approximately 8-10% (v/v) (normal gravity, NG fermentation), depending on the total solid (TS) content of the starting slurry. The low concentration of ethanol is then passed to steam distillation

and dehydration to yield anhydrous ethanol (99.5%).

Innovative Process for Transformation of Cassava to Bioethanol The innovative process for transformation of cassava to bioethanol starts with improving productivity of cassava at its origin – the farm. With the adoption of

drip irrigation and good farming practice, productivity can be increased from 19 tons/hectare to an average of 47 tons/hectar e (or 7.55 tons/rai). The huge advantage of this technology is that no new land needs to be cleared to produce bioethanol and the technology is suitable for small landholders.

Conventional Cassava Plantation with Inconsistent Size and Weight of Roots.

Innovative Cassava Cultivation Resulting in an Increase in Productivity and Root Size at 4 and 7 months, Respectively.

To further improve the overall process of ethanol production, the fermentation process called “High Gravity (HG)” or “Very High Gravity (VHG)” is utilized to

obtain a higher ethanol concentration up to 13-15 or 16-20% (v/v), respectively. The HG or VHG process uses higher soluble solid contents of TS or DS, greater than 25 or 30%, respectively.

Different forms of cassava, i.e. extracted starch, dried chips and fresh roots can be used for bioethanol production with different advantages and disadvantages To minimize the raw material cost, fresh roots are cheap during the harvest season and are of interest for bioethanol product ion. However, fresh roots, when

ground and mixed with water, produce thick and less fluid slurry, unless more water is added, resulting in a low total solid content, as well as low ethanol con-

centration in the mash.

To effectively use fresh roots in bioethanol production, viscosity reduction enzymes (VRE) are introduced to pre-treat ground roots. Accordingly, the fermenta-tion at higher solid contents of ground fresh roots can be efficiently achieved with the fermentation efficiency up to 90%.

Improved Process for Transformation of Cassava to Bioethanol (NG = Normal gravity, HG = High gravity, VHG = Very high Gravity and VRE = Viscosity reduction enzymes)

Advantages and disadvantages of using different forms of cassava material for bioethanol production.

Ground fresh roots (30% total solids) before pretreatment. After pretreatment with Viscosity Reduction Enzymes.

The coupled “High Gravity or Very High Gravity-Simultaneous Saccharification and Fermentation (VHG-SSF)” process for the transformation of cassava roots to bioethanol greatly benefits industrial producers as

it reduces the roots-to-chips step, resulting in the reduction of resources and transportation cost;

it increases flexibility for in-factory supply management, since fresh roots are more available during harvesting season and easier to manage inside

the factory;

it reduces the use of resources and energy consumption;

it yields a higher concentration of ethanol from 8-10% (w/v) up to 18% (v/v); and

by almost doubling the ethanol concentration in the final stage, the VHG-SSF process helps increase the plant capacity.

This technology is increasingly being adopted by ethanol producers in Thailand as it only requires adaption to their existing equipment and processes.

Pilot Plant at KMUTT Bangkhuntien Campus Demonstrating VHG-SSF Technology.

This fact sheet was produced by Dr. Kuakoon Piyachomkwan, January 2016.

Transformation of Cassava to Bioethanol Technology Package

1. Improved productivity of cassava root production Increased productivity 19t/h to 47 t/h without the change in

cassava variety

Adoption of new soil conservation practices

Increased avoided emissions

2. Improved in-factory raw material management and pre-fermentation practices

Increased flexibility for in-factory supply management

Reduced water, energy and resource consumption

Reduced transportation cost between farmers and factory

Lowered average cost of bioethanol production

3. Improved fermentation process Increased ethanol concentration using VHG-SSF technology

Increased plant capacity

Reduced energy usage in distillation

Increased avoided emissions