Microorganisms that dominate bio-leaching at 50°C (122°F) include Acidithiobacillus caldus and some Leptospirillum spp. At temperatures greater than 65°C (149°F), bio-mining microbial consortia are dominated by archaea rather than bacteria with species of Sulfolobus and Metallophores being most prominent.
Thus, biomining has developed into a successful and expanding area of biotechnology and the process employs microbial consortia that are dominated by acidophilic, autotrophic iron- or sulfur-oxidizing prokaryotes. Mineral bio-oxidation takes place in highly aerated, continuous-flow, stirred-tank reactors or in irrigated dump or heap reactors, both of which provide an open, non-sterile environment. Continuous-flow, stirred tanks are characterized by homogeneous and constant growth conditions where the selection is for rapid growth, and consequently, tank consortia tend to be dominated by two or three species of microorganisms. In contrast, heap reactors provide highly heterogeneous growth environments that change with the age of the heap, and these tend to be colonized by a much greater variety of microorganisms. Heap microorganisms grow as biofilms that are not subject to washout, and the major challenge is to provide sufficient biodiversity for optimum performance throughout the life of a heap.
Currently, a variety of biotechnological processes are being given serious consideration as options to the more conventional recovery methods for energy production. During the energy crisis that commenced in the 1970s, a bioleaching process was applied to oil shale in the United States in order to produce shale oil. Sulfur is actually introduced to the fractured oil shale blocks, and Thiobailli thiooxidans is used to generate a large amount of 0.1 N sulfuric acid to remove carbonate minerals. With Green River oil shale, 43% of the carbonates can be removed so that a more porous oil shale rock will remain. More oil can be produced from this treatment method due to the improved heat transfer efficiency upon retorting.
See also: Bacteria.
Bagasse
Bagasse is the dry pulpy residue left after the extraction of juice from sugar cane, used as fuel for electricity generators and other forms of energy. In addition, bagasse is 100% compostable, and if it does enter our environment, it will break down into soil entirely naturally, without any human intervention or additional processing.
More specifically, bagasse is the fibrous residue remaining after sugarcane or sorghum stalks are crushed to extract their juice and is currently used as a renewable resource in the manufacture of pulp and paper products and building materials. 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 to the consumer electricity grid.
Sugarcane bagasse is the major by-product of the sugar cane industry and contains approximately 50% w/w cellulose, 25% w/w hemicellulose, and 25% w/w lignin. Due to its abundant availability, the bagasse can serve as an ideal substrate for microbial processes for the production of value-added products such as protein-enriched animal feed, enzymes, amino acids, organic acids, and compounds of pharmaceutical importance.
The utilization of organic and agricultural residues such as bagasse for energy production is considered an important part in any strategy to achieve renewable energy goals and to reduce waste disposal and environmental pollution. For energy production, bagasse can be burned as a raw product or in the form of briquettes. Currently, most sugar cane bagasse is burned in boilers to produce steam which is utilized in factories and to power turbines for the production of electricity (cogeneration).
The combustion of sugar cane bagasse yields ash (bottom ash and fly ash) that contains high amounts of organic matter (charcoal and sugar cane bagasse debris) and inorganic components (on the order of 65% w/w).
One of the significant applications of bagasse is the production of protein-enriched cattle feed and enzymes. Bagasse could also be used for the production of industrially important enzymes and biofuel.
See also: Agave Bagasse, Bagasse Briquettes, Biomass, Sugarcane, Sugar Crops, Sugars and Starch.
Bagasse Briquettes
Bagasse is the fibrous residue remaining after sugarcane or sorghum stalks, for example, are crushed to extract their juice. It is currently used as a renewable resource in the manufacture of pulp and paper products and building materials. However, surplus bagasse presents a disposal problem for many sugar factories. Briquetting technology offers a way to reduce the surplus amount of bagasse.
A briquette (also spelled briquet) is a compressed block of (typically) combustible material (such as charcoal, sawdust, and wood chips) used for fuel. In some cases, the briquettes may be used for transportation before further processing. A piston press is used to create solid briquettes for a wide array of purposes. Screw extrusion is used to compact biomass into loose, homogeneous briquettes that are substituted for coal in cofiring. This technology creates a toroidal (doughnut-like) briquette.
The briquetting process involves the following steps: (i) size reduction in which the bagasse is chopped, rolling, or hammered, (ii) drying in which moisture is removed by open air drying or by using forced, heated air in a large rotating drum, (iii) carbonization in which the bagasse is combusted in a limited supply of oxygen in a buried pit or trench until it carbonizes into charcoal, (iv) feedstock preparation in which the carbonized bagasse is mixed with a binder such as clay or molasses, (v) compaction and extrusion in which the material is passed through a machine-operated or manually-operated extruder to form rolls of charcoal, (vi) drying in which the rolls are air-dried for 1 to 3 days, causing them to break into chunks, and (vii) packaging in which the briquettes in are made ready for sales.
See also: Agave Bagasse, Bagasse.
Baghouse
The baghouse (also known as a baghouse filter, bag filter, fabric filter, or fabric collector) uses filtration to separate dust particulates from particle-laden gases. They are one of the most efficient and cost-effective types of dust collectors available and can achieve a collection efficiency of more than 99% for fine particulates. A baghouse can be engineered for almost any dust producing application under almost any set of circumstances. In the cleaning process, particle-laden gases enter the baghouse and pass through a series of fabric bags that act as filters. The bags can be made of woven or felted cotton, synthetic, or glass-fiber material in either a tube or envelope shape.
The high efficiency of these collectors is due to the dust cake formed on the surfaces of the bags. The fabric primarily provides a surface on which dust particulates collect through the following mechanisms which are (i) inertial collection in which dust particles strike the fibers placed perpendicular to the gas-flow direction instead of changing direction with the gas stream, (ii) interception in which particles that do not cross the fluid streamlines come in contact with fibers because of the fiber size, and (iii) electrostatic forces in which the presence of an electrostatic charge on the particles and the filter can increase dust capture. A combination of these mechanisms results in formation of the dust cake on the filter, which eventually increases the resistance to gas flow. The filter must be cleaned periodically.
Baghouses come in design classifications based on the manner by which the bags are cleaned: (i) the pulse jet system, which uses high-pressure air directed down into the clean side of a filter bag in order to remove the dust cake from the surface of the media, (ii) the shaker style system, which involves shaking the bags in order to mechanically release the dust cake, and (iii) the reverse air system
