Organics, what are they?
Many of the substances troublesome to water plant operators are termed “organic.” What does organic mean. There seems to be some confusion about this term. Some people say carbon is organic. While its true that a lot of carbon in the earth such as coal was organic at one point, it is inaccurate to call carbon organic. Coal is the decomposition product from plant and animal species which lived millions of years ago. It is basically carbon with all the organic material decomposed.
So what is organic material? Organic chemistry encompasses the millions of variations of carbon compounds. All organic material contains carbon but not all carbon is organic. These carbon compounds are naturally occuring such as the ones derived from petroleum and synthetic ones such as those made in laboratories by reacting organic compounds with other compounds, Pharmacuticals are an example of synthetic organic compounds.
In water treatment we talk about TOC (total organic carbon), THMs (trihalomethanes), HAAs (haloacetic acids). TOC is a method by which all the organic material in a water sample is reacted to form carbon by itself and then the amount is measured. Trihalomethanes are methane which has halogens (chlorine or bromine) reacted with it to form a new organic compound. Haloacetic acids are acetic acid reacted with halogens to form a new compound. In both of these cases a substance present in the water prior to treatment, methane and acetic acid have reacted with chlorine or bromine to form a new molecule which is hazardous to humans Methane is carbon with four hydrogen ions attached to it. It is a very basic organic compound. Trihalomethane is methane with three of the hydrogens replaced by chlorine or bromine. Acetic acid is an organic acid with two carbon atoms attached together with hydrogen and oxygen attached to the two carbons. When this reacts with chlorine or bromine it forms haloacetic acid, a new organic compound which is hazardous to humans.
Organic compounds can be as simple as methane with a molecular weight of 16 and as complex as a protein or a DNA molecule which can have a molecular weight in the millions. Water treament polymers are good examples of larger organic molecules. In fact the term polymer refers to classes of organic compounds.
So, while all organic molecules contain carbon, not all carbon is organic. Activated carbon used in water treatement is just that, carbon. It can be derived from many different sources such as wood, coal, and other more specialized sources such as coconut shell. Its value comes from the tiny pores which can trap molecules, especailly organic moleculles which tend to be larger. It is therefore effective in removing organics from raw water prior to chlorination. Other techniques used to lower orgainc carbon are UV llight and oxidizers such as potassium permanganate. Many organic compounds react with UV light and oxidizers to form smaller molecules. Complete destruction of organic compounds results in carbon dioxide being formed from the carbon. There is some controversy about it, but carbon dioxide is not generally considered as an organic compound.
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