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Aluminum Residual Reduction

The USEPA has established 0.2 mg/l as a “secondary” maximum concentration limit for Al in finished water. This limit was established based on taste and color issues, rather than for any documented health issues.

High finished water Al levels are generally associated with the use of alum.  Specific causes include: a) using alum at dosages such that its alkalinity demand exceeds the raw water alkalinity, b) using alum to treat raw waters such that the settled water pH exceeds 8.5, or c) operating the filters beyond the point of turbidity breakthrough. Remedies are cause-specific, as follows:

  • If alum’s alkalinity demand exceeds the available raw water alkalinity, then additional alkalinity (usually in the form of lime) can be added prior to alum addition, or alum can be replaced with a coagulant having a lower alkalinity demand—for example, an aluminum chlorohydrate (ACH) or a Clar+Ion alum/polymer blend
  • If alum treatment is generating too high of a settled water pH, than:  a) an appropriate amount of acid (usually H2SO4) can be added prior to alum addition, b) alum can be replaced with either an appropriate acid-alum or an ACH. (Note:  due to their chemical structure, ACH has a higher operating pH than alum) or  c) a source of orthophosphate can be added prior to alum addition to precipitate soluble Al.
  • A filter-aid can be used to reduce filtered turbidities.
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