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Sulphide in freshwater

Sulphide occurring in freshwater

What is sulphide?
Hydrogen sulphide is a colourless, flammable gas under normal conditions. It is commonly known as stink damp, and sewer gas because it smells like rotten eggs. People can smell it at low levels. Hydrogen sulphide is formed as a result of decomposing animal manure. The decomposition process begins as soon as the animals excrete it. Microorganisms utilize the manure to synthesize new cellular material and to furnish energy for synthesis. This process takes place with or without oxygen. However, the type of microbes, and the type of gases that are produced, are dependent on the type of environment in which degradation takes place. In anaerobic conditions (without oxygen), typical of most liquid manure systems, hydrogen sulphide will be given off.
Hydrogen sulphide is also very corrosive (both in water and in the air). It rapidly tarnished silver causing it to turn black. High sulphide content is toxic to aquarium fish. As this water is brought to the surface for use, the unpleasant smelling hydrogen sulphide gas may be released.

A characteristic feature of hydrogen sulphide is that the gas is heavier by weight as normal air is. It is a highly toxic gas, which interferes with cellular respiration just like carbon monoxide and hydrogen cyanide. It is not simply a byproduct of some chemical processes but it can arise from some other sources eg decomposition of organic matter such as sewage, which in some instances has generated highly toxic, even fatal concentrations.


Who produces sulphide?
Hydrogen sulphide is not merely a smelly nuisance from stink bombs or rotten eggs.
It can also result from bacterial breakdown of organic matter. Human and animal wastes also produce it. Bacteria found in your mouth and gastrointestinal tract produce hydrogen sulfide from bacteria decomposing materials that contain vegetable or animal proteins. Hydrogen sulfide can also result from industrial activities, such as food processing, coke ovens, kraft paper mills, tanneries, and petroleum refineries.
Hydrogen sulphide occurs naturally in crude petroleum, natural gas, volcanic gases, and hot springs. It can also result from bacterial breakdown of organic matter.
It is released primarily as a gas and will spread in the air and may remain in the air for about 18 hours. When released as a gas, it will form sulphur dioxide and sulphuric acid in the atmosphere.

Sulphide in freshwater
Hydrogen sulphide can cause acid deposition on water and soil.
Sulphur dioxide hydrolyzes to sulfurous acid solution when it is in contact with water. Sulfurous acid is very soluble in water, and even low concentrations of sulphur dioxide or sulfurous acid in water is detrimental to aquatic life. If a release of sulfur dioxide occurs near a river or other body of water, the release has the potential to kill fish and other aquatic life.
Hydrogen sulphide is also a product of organic wastes, because when eutrophication in freshwater takes place, anaerobic organisms then attack the organic wastes, releasing gases such as methane and hydrogen sulphide, which are harmful to the oxygen-requiring (aerobic) forms of life. The result is a foul-smelling, waste-filled body of water. This has already occurred in such places as Lake Erie and the Baltic Sea, and is a growing problem in freshwater lakes all over India. Eutrophication can produce problems such as bad tastes and odours as well as green scum algae. Also the growth of rooted plants increases, which decreases the amount of oxygen in the deepest waters of the lake. It also leads to the death of all forms of life in the water bodies.

Read more about nutrients in freshwater

What sulphide due to humans
When we drink water that has been contaminated with hydrogen sulphide, it is known to cause nausea, illness and in extreme cases, death. High concentrations of dissolved hydrogen sulphide can also foul the bed of an ion exchange softener. Their continued presence will lead to lower and lower capacity and may finally necessitate replacement of the resin bed. Generally, hydrogen sulphide occurs in concentrations of less than 10 ppm. Occasionally, the amount goes as high as 50 to 75 ppm. Hydrogen sulphide is more common to well waters than to surface water supplies.

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