Other impurities

•           Iron

Iron, which makes up 5% of the earth's crust, is a common water contaminant. It can be difficult to remove because it may change valence states - that is, change from the water-soluble ferrous state (Fe2+) to the insoluble ferric state (Fe3+). When oxygen or an oxidizing agent is introduced, ferrous iron becomes ferric which is insoluble and so precipitates, leading to a rusty (red-brown) appearance in water.

This change can occur when deep well water is pumped into a distribution system where it adsorbs oxygen. Ferric iron can create havoc with valves, piping, water treatment equipment, and water-using devices.

Certain bacteria can further complicate iron problems. Organisms such as Crenothrix, Sphaerotilus and Gallionella use iron as an energy source. These iron-reducing bacteria eventually form a rusty, gelatinous sludge that can plug a water pipe. When diagnosing an iron problem, it is very important to determine whether or not such bacteria are present.

•                       Manganese

Although manganese behaves like iron, much lower concentrations can cause water system problems. However, manganese does not occur as frequently as iron. Manganese forms a dark, almost black, precipitate.

•                       Sulfate

Sulfate (S042~) is very common. When present at lower levels, sulfate salts create problems only for critical manufacturing processes. At higher levels, they are associated with a bitter taste and laxative effect. Many divalent metal-sulfate salts are virtually insoluble and precipitate at low concentrations.

•                       Chloride

Chloride (Cl~) salts are common water contaminants. The critical level of chloride depends on the intended use of the water. At high levels, chloride causes a salty or brackish taste and can interfere with certain water treatment methods. Chlorides also corrode the metals of water supply systems, including some stainless steels.

•                       Total Organic Carbon (TOC)

TOC is a direct measure of the organic, oxidizable, carbon-based material in water. TOC is a vital measurement used in sophisticated water treatment systems - such as electronics grade - where any amount of contamination can adversely affect product quality and yield.

•           Biochemical Oxygen Demand (BOD)

BOD is a measure of organic material contamination in water, specified in mg/L. BOD is the amount of dissolved oxygen required for the biochemical decomposition of organic compounds and the oxidation of certain inorganic materials (e.g., iron, sulfites). Typically the test for BOD is conducted over a five-day period.

•           Chemical Oxygen Demand (COD)

COD is another measure of organic material contamination in water specified in mg/L. COD is the amount of dissolved oxygen required to cause chemical oxidation of the organic material in water.

Both BOD and COD are key indicators of the environmental health of a surface water supply. They are commonly used in waste water treatment but rarely in general water treatment.

   [ Main ] [ Up ]