Water supplies meeting treatment requirements

Water Treatment & Disinfection Byproducts (DBPs)

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Disinfection Byproducts (DBPs)

 

Lake Superior

Summary

• Disinfection byproducts are a group of chemicals formed in low levels when disinfectants like chlorine interact with organic compounds naturally found in drinking water and have been linked to cancer in humans
• DBPs have different maximum contaminant levels ranging between 0.01 – 1 mg/L depending on jurisdiction and type
• Water treatment managers may reduce the levels of DBPs in treated water by replacing chlorine as a disinfectant or performing total organic carbon removal through enhanced coagulation, enhanced softening, and activated carbon adsorption

Where does it come from?

Disinfection byproducts (DBP) are a group of chemicals formed in low levels when disinfectants like chlorine interact with organic compounds naturally found in drinking water.[1] Disinfection, done through processes such as chlorination, is an important step in water treatment to reduce waterborne illnesses from viruses and bacteria and is required by the U.S. EPA and Health Canada [10] . Disinfection agents interact with organic compounds such as humic and fulvic acids sourced from agricultural runoff, aquifers, and natural vegetation to form DBPs.[4] The more total organic carbon (TOC) present in the water source, the higher chance of DBP formation. The design and operation of the water systems (e.g. water age) can also influence the likelihood of DBP formation.[2] Studies have demonstrated evidence for DBPs’ carcinogenicity in humans.[3]

How is it treated to meet applicable standards?

The U.S. EPA and Health Canada regulate the amount of several types of DBPs in drinking water. The Maximum Contaminant Level (MCL) for each is displayed in the chart below. [5,11]Depending on source water characteristics and other treatment goals, drinking water managers make decisions about how to meet these standards through the removal of TOC and the type of primary disinfectant. [6]

Type of DDBPUnited States EPAHealth Canada
Haloacetic acids (HAAs)0.06mg/L0.08mg/L
Total Trihalomethanes (TTHMs)0.08mg/L0.10mg/L
Chlorite1mg/L1mg/L
Bromate0.01mg/L0.01mg/L

Water treatment managers may reduce the levels of DBPs by selecting disinfectants other than chlorine. Alternative disinfectants include UV, chlorine dioxide, and chloramine. [6,7] UV lights are an expensive yet efficient disinfectant, though they require the use of a secondary disinfection system for residual disinfection within the distribution system. [6,7] Chlorine dioxide is also an effective disinfectant and oxidant. However, its extensive equipment makes it a more expensive option.[6] Utilizing chloramine as a secondary disinfectant will reduce the production of DBPs more inexpensively but may produce other toxins/disinfection by-products or extract lead from lead lines depending on the circumstances. [6,7]

TOC removal can be achieved through enhanced coagulation, enhanced softening, and activated carbon adsorption. [7,8] A combination of powdered activated carbon and enhanced coagulation has high removal efficiency (around 75%) to account for both high- and low-molecular weight organics. [7] Water supplies with high organic load may utilize granular activated carbon to effectively remove organics to reduce DBPs, but this method also requires high installation, operation, and maintenance costs.[7]

The process of drinking water treatment should be optimized from a system level to analyze the best method for DBP reduction based on source water chemistry, other treatment priorities, cost, and existing treatment infrastructure.[9]

References

 

  1. Water Quality & Health Council, In the Balance: Drinking Water Chlorination and Disinfection Byproducts (2020). Accessible online: https://waterandhealth.org/safe-drinking-water/treatment/in-the-balance-drinking-water-chlorination-and-disinfection-byproducts/
  2. Washington State Department of Health, Disinfection Byproducts—Chlorination of Drinking Water. Accessible online: https://doh.wa.gov/community-and-environment/drinking-water/disinfection/disinfection-byproducts
  3. CDC, Disinfection By-Products (2022). Accessible online: https://www.cdc.gov/healthywater/global/household-water-treatment/chlorination-byproducts.html
  4. American Water Works Association, Manual M20 Water Chlorination/Chloramination Practices and Principles (2006). Accessible online: https://www.awwa.org/Portals/0/files/publications/documents/M20LookInside.pdf
  5. EPA, National Primary Drinking Water Regulations. Accessible online: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#one
  6. WesTech Engineering, Strategies for Reducing Disinfection Byproducts. (2020). Accessible online: https://www.westech-inc.com/blog/strategies-for-reducing-disinfection-byproducts
  7. Parvez, S., Disinfection Byproducts: Treatment Options And Challenges For Public Water Suppliers. Water Online (2014). Available online: https://www.wateronline.com/doc/disinfection-byproducts-treatment-options-and-challenges-for-public-water-suppliers-0001#:~:text=The%20removal%20of%20precursor%20organics%20before%20disinfection%20prevents,quite%20affordable%20and%20commonly%20used%20by%20water%20suppliers.
  8. EPA, Comprehensive Disinfectants and Disinfection Byproducts Rules (Stage 1 and Stage 2): Quick Reference Guide. Accessible online: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100C8XW.txt
  9. EPA, Optimization to Reduce Disinfection Byproducts (DBPs). Accessible online: https://www.epa.gov/sdwa/optimization-reduce-disinfection-byproducts-dbps
  10. Government of Canada, Drinking Water Chlorination (2006). Accessible online: https://www.canada.ca/en/health-canada/services/healthy-living/your-health/environment/drinking-water-chlorination.html
  11. 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