Water supplies meeting treatment requirements

Water Treatment & Arsenic

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Arsenic

 

Lake Superior

Summary

  • Arsenic is a naturally occurring semi-metal which can contaminate water supplies naturally or from industry or agriculture, potentially leading to negative health effects
  • The current Maximum Contaminant Level for arsenic is 10 parts per billion for both the U. S. and Canada
  • Approved methods for arsenic treatment include adsorption, ion exchange, and coagulation with filtration but in some cases, pretreatment is required

What is arsenic?

Arsenic is a naturally occurring semi-metal element which can enter water supplies from both natural and human-made sources where it can lead to negative health effects. [1,2,3]

Where does it come from?

Arsenic is found naturally in soils and rocks but is also a pollutant from industry and agriculture. [1,2] Wood preservation, pesticide use, and byproducts from mining and coal burning can contribute to arsenic polluting groundwater. [1,2,4]

What are the contamination standards?

The current standard for arsenic is 10 ppb for both the U. S. EPA and Health Canada. [1,5]

How is drinking water treated to meet applicable standards?

Arsenic cannot be removed by boiling or disinfection and filters must be certified to remove arsenic. [2,3] The EPA list of approved methods for arsenic treatment includes adsorption, ion exchange, and coagulation with filtration.[6]

Adsorption removes arsenic by passing untreated pressurized water through granular media. These systems are lower cost, effective, and require minimal operator attention, however spent media needs to be disposed of as waste.

Ion exchange treats pressurized water through columns packed with anion exchange resin, which removes arsenic ions. The efficiency and cost of this system depends on the concentration of other anions and level of total dissolved solids. The resin can be regenerated or reconditioned, but the waste materials from this process need to be handled properly, increasing the price.

In coagulation, arsenic is precipitated out of solution using coagulates. These are then filtered out of the drinking water using filters. The cost and efficiency of this technique is dependent on several factors, though optimized systems can remove up to 90% of inorganic arsenic.

Reduced-form arsenic is often found in groundwater and must be oxidized with a chemical oxidizer for optimal removal. Arsenic can then be removed by adsorption or coprecipitation for filtration. Additionally, point-of-use techniques may be used at the point of a household sink to treat drinking water using reverse osmosis or activated alumina. These point of use systems do not necessarily address pre-oxidation and their price may be prohibitive for larger scale use.

References

 

  1. EPA, Chemical Contaminant Rules (2021). Accessible online: https://www.epa.gov/dwreginfo/chemical-contaminant-rules
  2. CDC, Arsenic and Drinking Water from Private Wells (2015). Accessible online: https://www.cdc.gov/healthywater/drinking/private/wells/disease/arsenic.html
  3. Costello, M. How to Protect Yourself and Your Family From Arsenic in Your Drinking Water (2021). NFS. Accessible online: https://www.nsf.org/blog/consumer/arsenic-drinking-water
  4.  Maine Division of Environmental and Community Health, Arsenic (2022). Accessible online: https://www.maine.gov/dhhs/mecdc/environmental-health/dwp/consumers/faq.shtml
  5. Government of Canada, Guidelines for Canadian Drinking Water Quality – Summary Table (2020). Accessible online: https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/water-quality/guidelines-canadian-drinking-water-quality-summary-table.html
  6. EPA, Arsenic in Drinking Water (2015). Accessible online: https://cfpub.epa.gov/safewater/arsenic/arsenictradeshow/arsenic.cfm?action=Treatment