Dec 17, 2007, 10:32 PM
Post #299 of 312
Re: [ayranjim] High Nitrates Level? Try This!
[In reply to]
Bacteria have a wide range of environmental and nutritive requirements.
Most bacteria may be placed into one of three groups based on their response to gaseous oxygen. Aerobic bacteria thrive in the presence of oxygen and require it for their continued growth and existence. Other bacteria are anaerobic, and cannot tolerate gaseous oxygen, such as those bacteria which live in deep underwater sediments, or those which cause bacterial food poisoning. The third group are the facultative anaerobes, which prefer growing in the presence of oxygen, but can continue to grow without it.
Bacteria may also be classified both by the mode by which they obtain their energy. Classified by the source of their energy, bacteria fall into two categories: heterotrophs and autotrophs. Heterotrophs derive energy from breaking down complex organic compounds that they must take in from the environment -- this includes saprobic bacteria found in decaying material, as well as those that rely on fermentation or respiration.
The other group, the autotrophs, fix carbon dioxide to make their own food source; this may be fueled by light energy (photoautotrophic), or by oxidation of nitrogen, sulfur, or other elements (chemoautotrophic). While chemoautotrophs are uncommon, photoautotrophs are common and quite diverse. They include the cyanobacteria, green sulfur bacteria, purple sulfur bacteria, and purple nonsulfur bacteria. The sulfur bacteria are particularly interesting, since they use hydrogen sulfide as hydrogen donor, instead of water like most other photosynthetic organisms, including cyanobacteria.
Bacteria play important roles in the global ecosystem.
The ecosystem, both on land, air and water, depends heavily upon the activity of bacteria.
The cycling of nutrients such as carbon, nitrogen, and sulfur is completed by their ceaseless labor.
Organic carbon, in the form of dead and rotting organisms, would quickly deplete the carbon dioxide in the atmosphere if not for the activity of decomposers. This may not sound too bad to you, but realize that without carbon dioxide, there would be no photosynthesis in plants, and no food. When organisms die, the carbon contained in their tissues is not available for most other living things. Decomposition is the breakdown of these organisms, and the release of nutrients back into the environment, and is one of the most important roles of the bacteria.
The cycling of nitrogen is another important activity of bacteria. Plants rely on nitrogen from the soil for their health and growth, and cannot acquire it from the gaseous nitrogen in the atmosphere. The primary way in which nitrogen becomes available to them is through nitrogen fixation by bacteria such as Rhizobium, and by cyanobacteria such as Anabaena, Nostoc, and Spirulina. These bacteria convert gaseous nitrogen into nitrates or nitrites as part of their metabolism, and the resulting products are released into the environment.
Some plants, such as liverworts, cycads, and legumes have taken special advantage of this process by modifying their structure to house the basteria in their own tissues. Other denitrifying bacteria metabolize in the reverse direction, turning nitrates into nitrogen gas or nitrous oxide. When colonies of these bacteria occur on croplands, they may deplete the soil nutrients, and make it difficult for crops to grow.
Denitrification is the process of reducing nitrate and nitrite, highly oxidized forms of nitrogen available for consumption by many groups of organisms, into gaseous nitrogen, which is far less accessible to life forms but makes up the bulk of our atmosphere. It can be thought of as the opposite of nitrogen fixation, which converts gaseous nitrogen into a more biologically available form. The process is performed by heterotrophic bacteria (such as Paracoccus denitrificans, Thiobacillus denitrificans, and various pseudomonads) from all main proteolytic groups. Denitrification and nitrification are parts of the nitrogen cycle.
Denitrification takes place under special conditions in both terrestrial and marine ecosystems. In general, it occurs when oxygen (which is a more favorable electron acceptor) is depleted, and bacteria turn to nitrate in order to respire organic matter.
Because our atmosphere is rich with oxygen, denitrification only takes place in some soils and groundwater, wetlands, poorly ventilated corners of the ocean, and in seafloor sediments.
Denitrification proceeds through some combination of the following steps:
nitrate Ā® nitrite Ā® nitric oxide Ā® nitrous oxide Ā® dinitrogen gas
Or expressed as a redox reaction:
2NO3- + 10e- + 12H+ Ā® N2 + 6H2O
Denitrification is the second step in the nitrification-denitrification process, the conventional way to remove nitrogen from sewage and municipal wastewater. It is also an instrumental process in riparian zones for the removal of excess nitrate from groundwater contaminated by fertiliser use.
Direct reduction from nitrate to ammonium (a process known as dissimilatory nitrate reduction to ammonium or DNRA) is also possible for organisms that have the nrf-gene. This is less common than denitrification in most ecosystems as a means of nitrate reduction.
Reduction under anoxic conditions can also occur through process called anaerobic ammonia oxidation (Anammox).
Anammox -acronym for anaerobic ammonium oxidation- is a recent addition to the knowledge on the nitrogen cycle. In this biological process, nitrite and ammonium are converted directly into dinitrogen gas. This process contributes up to 50% of the dinitrogen gas produced in the oceans. It is thus a major sink for fixed nitrogen and so limits oceanic primary productivity. The overall catabolic reaction is:
NH4+ + NO2- Ā® N2 + 2H2O.
The bacteria that perform the anammox process belong to the bacterial phylum planctomycetes, of which Planctomyces and Pirellula are the best known genera. Currently four genera of anammox bacteria have been (provisionally) defined: Brocadia, Kuenenia, Anammoxoglobus (all fresh water species), and Scalindua (marine species). The anammox bacteria are characterized by several striking properties: they all possess one anammoxosome, a membrane bound compartment inside the cytoplasm which is the locus of anammox catabolism.
Further, the membranes of these bacteria mainly consist of ladderane lipids so far unique in biology. Of special interest is the turnover of hydrazine (normally known as rocket fuel, and poisonous to most living organisms) as an intermediate. A final striking feature of the organism is the extremely slow growth rate: the doubling time is nearly two weeks!
The application of the anammox process lies in the removal of nitrogen in wastewater treatment. Instead of the conventional nitrification-denitrification process, only half of the nitrogen has to be oxidized partly to nitrite. For the enrichment of the anammox organisms a biofilm system seems to be especially suited in which the necessary sludge age of more than 20 days can be ensured.
Other possibilities are Sequencing Batch Reactors (SBR) or gas-lift-loop reactors using granular sludge. The cost reduction compared to conventional N-removal is considerable; the technique, however, is still young. The first full scale sludge-water treatment plant using the biological process of anammox was built 2000 in Germany (Hattingen). As of 2006 there are three full scale processes in The Netherlands. One on a municipal wastewater treatment plant (in Rotterdam and one on an industrial treatment plant (tannery) and one full scale application using SBR at the waste water treatment plant in Strass, Austria.
Aquaculture nitrogen waste removal: See--> United States Patent 7082893
(This post was edited by goldminer on Dec 17, 2007, 10:37 PM)