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Arcata Marsh tertiary treatment

30 bytes added, 21:50, 18 April 2008
Wastewater may contain high levels of [[nutrients]] such as nitrogen and phosphorus. The excessive release of these to the environment can cause the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). A rapid growth in the population of algae can result is an algal bloom of a magnitude such that the numbers are unsustainable. Eventually most of the algea die. The decomposition of the algae by bacteria uses up so much oxygen in the water that most or all of the animals living in the water die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus. Phosphorous is generally removed using chemicals such as alum, or ferric chloride which precipitate to form a salt and hydronium or hydroxide ions. These ions can cause the waters pH to fluctuate. Generally lime is used to stabalize the pH of the effluent. These reactions require a settling basin to remove the precipitants. Removing nitrogen can be accomplished using either chemical or biological processes. Nitrogen is generaly present in the form of amonia. The chemical process simply raises the pH of the effluent. This converts the amonia to amonium which can be removed from teh water simply by passing large quantities of oxygen through it. The biological process simply uses activated sludge for an extended period of time, typically around 15 days.<ref>Davis, Mackenzie L. and Susan J. Masten. Principles of Environmental Engineering and Science. New York. Mc Graw Hill. 2004.</ref>
[[Image:Phosphorous removal.gif| | left| awaiting permission.]]
=== Disinfection ===
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