Regulatory Limit (EPA MCL): 0.05 mg/L or 50 parts per billion (ppb)
Common Forms: Selenate (Se(VI)) and selenite (Se(IV))
Primary Health Concern: Long-term exposure above the MCL can cause selenosis, leading to brittle hair and nails, among other issues.
The choice of technology often depends on the selenium species present and other water quality factors.
| Technology | How It Works | Key Efficacy Notes |
|---|---|---|
| Reverse Osmosis (RO) | Forces water through a semi-permeable membrane that filters out contaminants. | Highly effective for both selenite and selenate. Often provides the highest removal efficiency. |
| Anion Exchange | Uses resin beads to exchange chloride or hydroxide ions for selenium anions in water. | Can remove 60-95% of selenium. Particularly effective for selenite. |
| Activated Alumina (AA) | An adsorption process where selenium compounds are trapped on the surface of alumina media. | Effective adsorbent, performance varies with pH and selenium species. |
| Coagulation/Filtration | Adds chemicals (e.g., iron salts) to form insoluble particles that bind selenium, then filters them out. | Converts soluble selenium into insoluble particles for removal. Effective, especially for selenite. |
| Biological Treatment | Uses microorganisms in anoxic conditions to reduce selenium to an insoluble elemental form. | Highly effective for high-concentration streams like industrial wastewater; less common for drinking water. |
| Iron-Based Adsorbents | Uses media like iron oxide or Zero Valent Iron (ZVI) to adsorb selenium onto their surface. | Highly effective for adsorbing both species, particularly selenite. |
Speciation is Critical: Selenium's form drastically affects treatability.
Selenite (SeIV): Generally easier to remove via adsorption, coagulation, or ion exchange.
Selenate (SeVI): More mobile and harder to remove; may require specialized resins, RO, or pretreatment.
Pretreatment: For selenate, pre-reduction (e.g., with ferrous iron) or other oxidation-state changes can significantly improve removal rates in some systems.
Monitoring & Testing:
Public Water Systems: The EPA requires annual Consumer Confidence Reports (CCRs) that list detected contaminant levels, including selenium.
Private Well Owners: Testing is essential. Consult with a water treatment professional to interpret results and select an appropriate system tailored to your water chemistry.
For Homeowners/Consumers: Check your utility's CCR for selenium levels. If you have a private well, test your water at a certified lab.
For System Selection: Work with a qualified water treatment professional. They can help identify the selenium species present and recommend the most effective technology (often RO for point-of-use, or anion exchange/AA for point-of-entry) based on your specific water quality and needs.
Disclaimer: This information is for educational purposes. Always consult with water quality professionals for diagnosis and treatment of your specific water supply.
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