Bagasse

Sugarcane being crushed in Engenho da Calheta, Madeira. The bagasse falls down a chute and is removed on a conveyor belt below.

Bagasse (pron.: /bəˈɡæs/ bə-GAS) is the fibrous matter that remains after sugarcane or sorghum stalks are crushed to extract their juice. It is currently used as a biofuel and in the manufacture of pulp and paper products and building materials.

Agave bagasse is a similar material that consists of the tissue of the blue agave after extraction of the sap.

Production, storage and composition

For each 10 tonnes of sugarcane crushed, a sugar factory produces nearly 3 tonnes of wet bagasse. Since bagasse is a by-product of the cane sugar industry, the quantity of production in each country is in line with the quantity of sugarcane produced.

The high moisture content of bagasse, typically 40 to 50%, is detrimental to its use as a fuel. In general, bagasse is stored prior to further processing. For electricity production, it is stored under moist conditions, and the mild exothermic reaction that results from the degradation of residual sugars dries the bagasse pile slightly. For paper and pulp production, it is normally stored wet in order to assist in removal of the short pith fibres, which impede the papermaking process, as well as to remove any remaining sugar.

A typical chemical analysis of bagasse might be (on a washed and dried basis):
Cellulose 45–55%
Hemicellulose 20–25%
Lignin 18–24%
Ash 1–4%
Waxes <1%

Bagasse is an extremely inhomogeneous material comprising around 30-40% of "pith" fibre, which is derived from the core of the plant and is mainly parenchyma material, and "bast", "rind", or "stem" fibre, which comprises the balance and is largely derived from sclerenchyma material. These properties make bagasse particularly problematic for paper manufacture and have been the subject of a large body of literature.

Use

Heaps of bagasse, covered with blue plastic, outside of a sugar mill in Proserpine, Queensland

Many research efforts have explored using bagasse as a renewable power generation source and for the production of bio-based materials.

Fuel

Bagasse is often used as a primary fuel source for sugar mills; when burned in quantity, it produces sufficient heat energy to supply all the needs of a typical sugar mill, with energy to spare. To this end, a secondary use for this waste product is in cogeneration, the use of a fuel source to provide both heat energy, used in the mill, and electricity, which is typically sold on to the consumer electricity grid.

The resulting CO₂ emissions are equal to the amount of CO₂ that the sugarcane plant absorbed from the atmosphere during its growing phase, which makes the process of cogeneration greenhouse gas-neutral^{[citation needed]}. In many countries (such as Australia), sugar factories significantly contribute 'green' power to the electricity supply. For example, Florida Crystals Corporation, one of America's largest sugar companies, owns and operates the largest biomass power plant in North America. The 140 MW facility uses bagasse and urban wood waste as fuel to generate enough energy to power its large milling and refining operations as well as supply enough renewable electricity for nearly 60,000 homes.

Ethanol produced from the sugar in sugarcane is a popular fuel in Brazil. The cellulose-rich bagasse is being widely investigated for its potential for producing commercial quantities of cellulosic ethanol. For example, BP Biofuels is operating a cellulosic ethanol demonstration plant based on cellulosic materials in Jennings, Louisiana.

Paper

Main article: Soda pulping

Around 5–10% of paper production worldwide is produced from agricultural crops, valuing agricultural paper production at between $5 and 10 billion. One of the most notable of these is bagasse. Paper production is the second-largest revenue stream from bagasse; the largest is electricity cogeneration. Using the by-products of agricultural crops for paper production, rather than wood, does offset commercial forestry practices. This is believed beneficial because the conversion of the rainforest to commercial tree stock and common forestry practices destroys a majority of the indigenous rainforest life forms. For example, the most common commercial tree stock for short fiber pulp for paper is eucalyptus, which is considered an invasive species due to compounds in the leaves that can be toxic in large quantities (i.e. on a tree farm), and because it is considered a fire hazard. A secondary benefit of substituting agricultural by-products for commercial forestry practices is the reduction of the number of farmers following logging roads into the rainforest for the purpose of burning pristine rainforests to convert to farming. It is thought that bagasse has the added advantage over other forms of papermaking feedstock in that it requires fewer greenhouse gases to collect, compared to harvesting of wood chips, as the fibre has already been transported to the factory for extracting the sugar. However, a full lifecycle analysis should be performed before using this claim commercially. Due to the ease with which bagasse can be chemically pulped, bagasse requires less bleaching chemicals than wood pulp to achieve a bright, white sheet of paper. The fibers vary in length depending on the country and cane variety but are typically about 1.3 to 1.7 mm long. Bagasse fibers are well suited for tissue, corrugating medium, newsprint, and writing paper.

Bagasse pulp and paper mills tend to be smaller than wood-based mills, although many world-scale factories exist. TNPL is the Largest bagasse-based Paper Mill in the world, consuming about one million tones of bagasse every year.

Most chemical bagasse pulp mills concentrate the spent reaction chemicals and combust them to power the paper mills and to recover the reaction chemicals.

Boards

It can also be used for making boards resembling Plywood or Particle board, namely Bagasse board. It has wide usage for making partitions, furniture etc. It is an eco-friendly method as it does not involve any harm to the world's timber resources, un-like plywood. It is known as Bagasse Board and is considered a good substitute for plywood.

Other uses

Bagasse's uses are wide and varied due to its widespread availability and low cost.

Health impact

Workplace exposure to dusts from the processing of bagasse can cause the chronic lung condition pulmonary fibrosis, more specifically referred to as bagassosis.

See also

• Biofuel
• Bioenergy

Further reading

• The Potential of Bagasse-Based Cogeneration in the US, Kevin Ho, Columbia University, 2006.