The Biomass Feedstock Development Program at Oak Ridge National Laboratory (ORNL) recently released a publication entitled Bamboo: An Overlooked Biomass Resource? Bamboo is the common term for a group of woody grasses comprised of 1250 species. It is relatively fast growing and attains maturity within five years. The shortest species stands only four inches (10 cm) at maturity while the tallest reach 130 feet (40 m) with stem (culm) diameters of 12 inches (30 cm).
Most bamboo species grow in the tropics; however, some varieties occur naturally in subtropical and temperate zones of all continents except Europe. The growing zone ranges from latitudes 46 °N to 47 °S and from sea level to over 13,000 feet (4,000 m) in elevation. Asia alone has over 1000 species, most of it in natural stands. Current major bamboo-producing-and-using countries include China, India, Bangladesh, Indonesia, and Thailand.
Approximately 1,500 commercial applications of bamboo have been identified. These applications may be divided into the following broad categories:
• Construction and reinforcing fibers—agricultural and fishing tools, handicrafts, musical instruments, furniture, civil engineering (bridges, scaffolding), and buildings (house frames, walls, window frames, roofs, interior dividers).
• Paper, textiles, and boards—this also includes rayon, plywood, oriented strand board, and laminated flooring.
• Food—bamboo shoots are widely used in Chinese and other Asian cuisine.
• Bioenergy feedstocks—no references were found in the literature concerning the use of bamboo as an energy feedstock.
A mature planting of bamboo forms a dense stand with little light penetration. Bamboo is semi-deciduous, with leaves shed at the end of the growing season or for species on a two-year cycle, during the following growing season. Plants that have a biennial pattern of leaf emergence typically also exhibit strong shoot production in the year when leaves are not shed.
One of the more interesting aspects about bamboo is its rapid growth. The plant will send out rhizomes (underground horizontal plant stems) tens of meters in all directions that are 12 to 20 inches (30 to 50 cm) beneath the surface. Shoot buds appear on the sides of these rhizomes, and with the onset of warm spring weather, the buds lengthen and form a compact upright shoot that penetrates the ground’s surface. The plant now concentrates on growing the culm, without branches, as fast as possible. Tall species of bamboo have been observed to grow as much as 20 inches (0.5 m) per week. After the shoot reaches the same height as other culms, leafy branches appear near the top of the culm. Growth over the following years consists of thickening the walls of the culm and increasing the wood density.
Another interesting phenomenon about bamboo is its flowering patterns. A few species are known to flower frequently, even annually, and a few species flower a few culms at a time.
However, for the majority of bamboo species, the entire clump at a location will produce flowers and then die back over the next two to three years. For most of the latter species, flowering happens every 30 to 40 years although for some species the period is over 60 years. This infrequency of flowering makes bamboo hard to study and partially accounts for the lack of knowledge about bamboo.
Since bamboo is propagated vegetatively by planting rhizomes, it may not be known where the plant is in its flowering cycle. This uncertainty of when flowering and die-back may occur has long been a concern with bamboo growers. However, the ORNL report states that “…the threat of catastrophic flowering need not pose an economic problem for bamboo growers, as long as uneven-aged propagation material is maintained, and entire stands are replaced before they approach flowering age.”
For fuel analysis, nine bamboo samples representing three different species at three different ages were collected. The publication lists the proximate, ultimate, and elemental analyses for these nine samples. The typical moisture content for freshly field-harvested bamboo is approximately 15 percent. The ash content of all samples was one percent or less, with no correlation between ash content and bamboo sample or age of sample apparent. This ash content is similar to other woody biomass materials.
Volatiles in the samples ranged from 63 to 75 percent with the balance fixed carbon and, again, no correlation between volatiles and bamboo sample or sample age was determined. Heating values were comparable to wood at 16 million to 16.5 million Btu/ton (19.09 to 19.57 GJ/t) on a dry basis.
Three bamboo characteristics—low nitrogen content, low chlorine content, and low alkali indices—are particularly significant for combustion of bamboo. Alkali indices (defined as pounds of alkali oxide per million Btu of energy content) range from 0.23 to 0.7 (0.1 to 0.3 kg/GJ), generally below the limit of 0.4 to 0.8 lb/MMBtu (0.17 to 0.34 kg/GJ) known to cause adverse fouling and slagging in combustion systems. The presence of chlorine has been shown to increase the volatility of alkali metals during combustion. However, the low chlorine values present in bamboo samples suggest that the potassium that is present is unlikely to be volatile and therefore not a problem.
Bamboo must be grown vegetatively and 1-2 year old rhizome cuttings of 12 to 20 inches (30 to 50 cm) in length with nodes and buds present are sometimes used. Younger rhizomes provide the best results. Propagation with rhizome cuttings with at least a foot of culm attached also gave better results. Typically up to eight years are required to achieve a good stand and the final stand height may not be reached until 15-20 years have elapsed.
Harvesting of traditionally grown bamboo is un-mechanized and labor intensive, especially if only selected culms are to be harvested. Research in India suggests that clear-cutting does not significantly damage bamboo stands, so it may be possible to use machinery such as modified sugar-cane harvesters. The Western and Southeastern Regional Biomass Energy Programs sponsored bamboo harvesting tests in Alabama in the late 1990’s using a flail-cutter-head harvester developed at Texas A&M Kingsville and obtained acceptable harvesting results for bamboo approximately 30 feet tall.
Bamboo has frequently been characterized as having a high productivity; however, the ORNL study did not substantiate this characterization. Values for productivity in the literature range from 1 ton/acre/year (2.2 t/ha/year) in Northern India to 7 tons/acre/year (15.5 t/ha/year) in Central Japan. Data from the United States is very limited. Data from stands in South Alabama that were aged 14 to 20 years averaged 2.7 to 3.9 tons/acre/year (6.1 to 8.6 t/ha/year). These figures exclude branches and leaves, which accounted for 14 percent of the above-ground biomass. The ORNL report speculates that based on figures available from overseas, as well as the limited trials conducted in the US, intensively managed bamboo stands with fertilization may be capable of producing over 4.5 tons/acre/year (10 t/ha/year) under Southeast US conditions.
For additional information, contact the American Bamboo Society, c/o Michael Bartholomew, 750 Krumkill Road, Albany, NY 12203-5976, http://www.bamboo.org/abs/index.shtml.
