In ecology, biomass refers to the entire mass of all living things in a given area or ecosystem at any one time. In other words, if you were to account for the mass of every living thing in a given area at a given time you would be calculating biomass for that area. According to most estimates, the total biomass of the earth is somewhere around 560 billion metric tons. Each year, roughly 146 billion tons of biomass are generated on the planet, mostly as a result of plant growth.
In recent years, the term " biomass" has been used by the biofuel industry to refer to biological material from a living, or recently living organism. More often than not, the term is used to refer to plant derived material. Biomass can be used directly or indirectly as a fuel. Direct uses are limited to thermal conversion, otherwise known as burning. Biomass can be indirectly used by either chemically or biologically converting it to another substance.
History of Biomass
Though many regard the use of biomass to generate energy as a recent development, it is actually the most ancient energy source known to humans. Wood, for instance, is biomass as are animal dung and peat. All of these have been burned for centuries in order to generate heat and to do basic work. Long before the internal combustion engine was developed, biomass in the form of wood with burned to generate the steam used to power locomotives.
Even today, wood is the largest single source of biomass energy. Wood is actually the least expensive means of generating heat, wood is becoming less frequently used because of its inconvenience. According to the United States Department of Agriculture, heat generated from wood chips cost approximately one third the amount that heat generated from natural gas does and about one-tenth that of electricity. Changes in the way in which energy is derived from wood are promising to make it a very clean, renewable, environmentally friendly fuel source for the generation of electricity moving forward.
Types of Biomass
Because the term "biomass" more often refers to plants than to animals, Only plants will be considered here. Plant biomass is commonly divided into two categories: woody and non-woody. Things like wood, oil palm, and coconuts fall under the guise of woody biomass. Most food crops fall under the category of non-woody biomass. Additionally, grasses, such as Switchgrass, also fall under the second heading.
The biggest difference between woody and non-woody biomass is replacement time. Woody biomass generally takes much longer to grow and thus requires more sophisticated management than does non-woody biomass. Either type can be used directly or can be chemically/biologically converted. In most cases, woody biomass is used directly whereas non-woody biomass is chemically converted. This trend is changing, however, as more and more biomass is being gasified before it is burned. The following is a look at some of the most common types of biomass used in energy production. Note that wood is broken down here into several categories.
- Woody Biomass
- Coconut - In areas with abundant coconut trees, after harvesting the meat or edible part of the coconut, the hull is converted into a bio briquette. The benefit of this biomass is that it burns efficiently and leaves very little residue. This has resulted in bio briquettes being used for cooking, particularly in underdeveloped countries.
- Oil Palm - The oil palm provides biomass in two ways. The fruit produces oil, which can be harvested and chemically converted to produce biodiesel. After the oil is harvested, however, the hulls can be burned directly. Thus, oil palm provide both direct and indirect biomass.
- Poplar - The poplar family includes trees like the Aspen and Cottonwood. These trees are valued for their rapid growth, reasonable resistance to disease, ability to provide habitat, and ability to be cultivated from sprouts cut from adult trees (reduces overall cost in the long term).
- Pine - Pine is valued for many of the same reasons as poplar. It grows fast, it's easy to cultivate, and is relatively inexpensive to grow.
- Non-woody Biomass
- Algae - Algae offers to tremendous benefits over most conventional biofuels. First, algae are easily manipulated using genetic engineering technology. This allows the organism to be modified to produce more useful oil and to require less nutrients. Second, algae can be grown in small spaces on marginal land. This means they're less of a threat to the food supply and theoretically could replace the all fossil fuels.
- Corn - The biggest benefit for corn is that it's already grown in relative abundance. The United States is the world leading producer of corn and, not surprisingly, the world leading producer of ethanol made from corn. Each year, a larger and larger percentage of corn produced in the United States is used to make fuel ethanol. Unfortunately, the yield per acre of ethanol produced from corn is relatively low in the net impact of using so much corn to produce fuel ethanol has been an increase in global food prices and bus and increase in rates of starvation.
- Grasses - A number of different grasses have been suggested as potential biofuel feedstock. The most commonly discussed is Switchgrass. Switchgrass has the potential to be used both directly and indirectly. Its high cellulose content makes it an ideal direct biomass. In some settings it is burned directly whereas in others it is mechanically converted into pellets for easy transportation and storage. As the ability to generate ethanol from cellulosic continue to advance, Switchgrass become a more and more attractive option for this as well. The benefits of switch grass over other biomass include:
- Perennial (lowers costs)
- Improved soil quality from not plowing each year
- Relatively high yield on marginal land not suitable for food production
- Drought and pest resistant
- Low water and fertilizer needs
- Soybean - At this point, soybean is generally not considered a suitable candidate for large-scale biomass production. This is because it requires relatively high amounts of water and fertilizer, has a low yield per acre, and is relatively expensive to cultivate.
- Sugar cane - The potential of sugarcane to act as a biomass feedstock depends on the location in which is planted. In Brazil, for instance, where sugar cane has been cultivated for decades, environmental impact of using it as a fuel is relatively limited. In other locations, South Africa, sugar cane does not have a long history of cultivation. In the settings, the impact of using sugar cane as a biomass can actually be greater than the impact of traditional fossil fuels.