## 2.4 Biomass types

Feedstock is the renewable raw material (biomass) that is converted into marketable products in a biorefinery. Today, biomass sources for biorefinery are typically provided from six different categories:

1. Agricultural crops & residues

2. Sewage

3. Municipal solid waste

4. Animal residues

5 Industrial residues

6. Forestry crops & residues

Types of biomass

Types of biomass, especially when used as biofuels, are often categorized in yet another way. This categorization occurred as a result of the food versus fuel dilemma. Food versus fuel is the dilemma regarding the risk of diverting farmland or crops for biofuels production to the detriment of the food supply. Biofuel production has increased in recent years. Some commodities like maize (corn), sugar cane or vegetable oil can be used either as food, feed, or to make biofuels. For example, since 2006, a portion of land that was also formerly used to grow other crops in the United States is now used to grow corn for biofuels, and a larger share of corn is destined to ethanol production, reaching 25% in 2007. Second and third generation biofuels could potentially solve the dilemma's that arose from this food versus fuel discussion.

First-generation products are created largely from feedstocks that have traditionally been used as food. A classic example is the use of starch from maize (corn) for biofuels. Starch can easily be converted into useful products, such as ethanol or lactic acid.

Second-generation products are made from non-food feedstocks using advanced technical processes. Cellulosic ethanol is the most developed second-generation biofuel and is produced from the cellulose or cell wall of plant cells. The use of second generation feedstocks do not compete with the food supply for humans. At disadvantage is, however, that the cellulose is more difficult to break down than starch.

Third-generation products, like second-generation biofuels, are made from non-food feedstocks, but are harvested from non-arable land e.g. water. Typical examples are duckweed and algae. Growing third generation biomass is not demanding land and it is thus not competing in any way with growing for food.