reach the bacteria. Because hydrogen buildup hinders further production, there further has to be a continuous removal of the hydrogen produced, by pipelines to, for example, a shore location, where gas treatment and purification can take place. These requirements make it little likely that equipment cost can be kept so low that the low efficiency can be tolerated.
A further problem is that if the bacteria are modified to produce maximum hydrogen, their own growth and reproduction are quenched. Presumably, there has to be made a compromise between the requirements of the organism and the amount of hydrogen produced for export, so that replacement of organisms (produced at some central biofactory) does not have to be made at frequent intervals. The implication of this is probably an overall efficiency lower than 0.05%.
In a life-cycle assessment of bio-hydrogen produced by photosynthesis, the impacts from equipment manufacture are likely substantial. To this, one should add the risks involved in production of large amounts of genetically modified organisms. In conventional agriculture, it is claimed that such negative impacts can be limited, because of the slow spreading of genetically modified organisms to new locations (by wind or by vectors such as insects, birds, or other animals).
In the case of ocean bio-hydrogen farming, the unavoidable breaking of some of the glass- or transparent plastic-covered panels will allow the genetically modified organisms to spread over the ocean involved and ultimately the entire biosphere. A quantitative discussion of such risks is difficult, but the negative cost prospects of the biohydrogen scheme probably rule out any practical use anyway.
Biopower
Biopower (biomass power, renewable electric energy) is the use of biomass feedstock to produce electric power or heat through direct combustion of the feedstock, through biopower system technologies (such as: direct-firing, co-firing, gasification, pyrolysis, and anaerobic digestion), gasification and then combustion of the resultant gas, or through other thermal conversion processes. Power is generated with engines, turbines, fuel cells, or other equipment.
Most biopower plants use direct-fired systems. They burn bioenergy feedstocks directly to produce steam. This steam drives a turbine, which turns a generator that converts the power into electricity. In some biomass industries, the spent steam from the power plant is also used for manufacturing processes or to heat buildings. Such combined heat and power systems greatly increase overall energy efficiency. Paper mills, the largest current producers of biomass power, generate electricity or process heat as part of the process for recovering pulping chemicals.
Co-firing refers to mixing biomass with fossil fuels in conventional power plants. Coal-fired power plants can use co-firing systems to significantly reduce emissions, especially sulfur dioxide emissions. Gasification systems use high temperatures and an oxygen-starved environment to convert biomass into synthesis gas, a mixture of hydrogen and carbon monoxide. The synthesis gas (syngas) can be converted into other fuels or products, burned in a conventional boiler, or used instead of natural gas in a gas turbine. Gas turbines are very much like jet engines, only they turn electric generators instead of propelling a jet. Highly efficient to begin with, they can be made to operate in a “combined cycle,” in which their exhaust gases are used to boil water for steam, a second round of power generation, and even higher efficiency.
Using a similar thermochemical process but different conditions (totally excluding rather than limiting oxygen, in a simplified sense) will pyrolyze biomass to a liquid rather than gasify it. As with syngas, pyrolysis oil can be burned to generate electricity or used as a chemical source for making plastics, adhesives, or other bioproducts.
The natural decay of biomass produces methane, which can be captured and used for power production. In landfills, wells can be drilled to release the methane from decaying organic matter. Then, pipes from each well carry the methane to a central point, where it is filtered and cleaned before burning. This produces electricity and reduces the release of methane (a very potent greenhouse gas) into the atmosphere.
Methane can also be produced from biomass through a process called anaerobic digestion. Natural consortia of bacteria are used to decompose organic matter in the absence of oxygen in closed reactors. Gas suitable for power production is produced, and possibly troublesome wastes (such as those at sewage treatment plants or feedlots) are turned to usable compost.
Gasification, anaerobic digestion, and other biomass power technologies can be used in small, modular systems with internal combustion or other generators. These could be helpful for providing electrical power to villages remote from the electrical grid—particularly if they can use the waste heat for crop drying or other local industries. Small, modular systems can also fit well with distributed energy generation systems.
See also: Bioenergy, Biofuels, Biomass to Energy.
Bioprocess
A bioprocess is any process that uses complete living cells or organisms or their components (e.g., bacteria, enzymes) to effect desired a physical change and/or a chemical change in the feedstock. Transport of energy and mass is fundamental to many biological and environmental processes.
Modern bioprocess technology used this principle and is actually an extension of older methods for developing useful products by taking advantage of natural biological activities. Although more sophisticated, modern bioprocess technology is based on the same principle: combining living matter (whole organisms or enzymes) with nutrients under the conditions necessary to make the desired end product. Bioprocesses have become widely used in several fields of commercial biotechnology, such as production of enzymes (used, for example, in food processing and waste management) and antibiotics.
Since bioprocesses use living material, they offer several advantages over conventional chemical methods of production. Bioprocesses usually require lower temperature, pressure, and pH (the measure of acidity) and can use renewable resources (biomass) as raw materials. In addition, greater quantities can be produced with less energy consumption.
In most bioprocesses, enzymes are used to catalyze the biochemical reactions of whole microorganisms or their cellular components. The biological catalyst causes the reactions to occur but is not changed. After a series of such reactions (which take place in large vessels (fermenters or fermentation tanks), the initial raw materials are chemically changed to form the desired end product. Nevertheless, there are challenges to the use of bioprocesses in the production of synthetic fuels.
First, the conditions under which the reactions occur must be rigidly maintained. Temperature, pressure, pH, oxygen content, and flow rate are some of the process parameters that must be kept at specific levels. With the development of automated and computerized equipment, it is becoming much easier to accurately monitor reaction conditions and thus increase production efficiency.
Second, the reactions can result in the formation of many unwanted by-products. The presence of contaminating waste material often poses a two-fold problem related to (i) the means to recover (or separate) the end product in a way that leaves as little residue as possible in the catalytic system, and (ii) the means by which the desired product can be isolated in pure form.
See also: Bioconversion Platform.
Bioreactor
One of the major areas of research concerning landfill is the use of bioreactors. A bioreactor is formed under specific land filling conditions. Bioreactor land filling is a process in which water and air are circulated into a specially-designed landfill, in order to cause accelerated biological decomposition of the waste material. The intention for this type of landfill operation
