United States
Environmental Protection
Agency
RESEARCH PROJECT
National Risk Management Research Laboratoi
Water Supply and Water Resources Division
Treatment Technology Evaluation Branch
THE EFFECT OF WATER CHEMISTRY ON THE REMOVAL OF ARSENIC FROM DRINKING
WATER DURING IRON REMOVAL TREATMENT
IMPACT STATEMENT
New health effects research prompted the U.S.
Environmental Protection Agency (EPA) to reduce the
drinking water standard for arsenic from 0.05 to 0.010
milligrams (mg) I"1 (10 micrograms (u.g) I"1), and as a result
many drinking water systems, particularly smaller ones,
throughout the country will no longer be in compliance. A
number of technologies are currently available to remove
arsenic from water. In waters that contain natural iron,
arsenic removal can be achieved during iron removal, but
the effectiveness of iron to remove arsenic depends on
many variables. The objective of this study was to identify
the operational and water quality factors that impact
arsenic removal during iron removal. The findings of this
study will help EPA provide guidance and solutions that
may lead to best available technologies for the co-removal
of iron and arsenic, particularly for small systems facing unique compliance challenges.
BACKGROUND:
The new arsenic standard for drinking water will require thousands of drinking water systems to install arsenic removal
technology. Arsenic, which is found at varying levels in many groundwaters and some surface waters, can have both
natural and anthropogenic sources. In natural environments, high levels of arsenic are generally caused by the leaching
of arsenic from certain arsenic-containing minerals, such as arsenopyrite and other various arsenic sulfides and
sulfosalts. In addition to arsenic-bearing host minerals, discharge from various industries (including mining, petroleum
refining, and glass and ceramics manufacturing) can cause arsenic pollution. Pesticides, herbicides and fertilizers are also
known sources of arsenic release. Treatment methods for the removal of arsenic from water include coprecipitation
processes using iron and aluminium salts, iron removal, anion exchange, lime softening, reverse osmosis, electrodialysis
reversal (EDR), nanofiltration and adsorption media. Many arsenic removal processes are iron-based treatment
technologies, such as chemical coagulation with iron salts, natural iron removal from source waters by oxidation and
filtration, and iron-based adsorptive media. These processes are particularly effective at removing arsenic from aqueous
systems because iron surfaces have a strong affinity to adsorb arsenic. As a result, the adsorption and coprecipitation of
arsenate and arsenite on iron oxide surfaces have been investigated extensively. Due to geochemistry, many arsenic-
containing groundwaters also contain significant levels of iron (Fe), which is typically in the reduced (i.e. dissolved) Fe(ll)
state. In these cases, conventional Fe removal processes can be used to reduce arsenic by taking advantage of the
surface adsorptive capacity of natural iron particles that are produced following the oxidation of Fe(ll). The capacity to
remove arsenic during iron removal depends largely on the amount of arsenic and natural Fe present in the source
water.
National Risk Management Research Laboratory
Water Supply and Water Resources Division
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DESCRIPTION:
This research investigates the effects of water chemistry, oxidant type and concentration on the removal of iron and
arsenic from drinking water. The research will be conducted using one of the National Risk Management Research
Laboratory's Water Supply and Water Resources Division's current drinking water treatment pilot plants. Suspension
color, turbidity, pH, and iron and arsenic levels will be regularly monitored during pilot plan runs. The impact of water
quality including calcium, chlorine, orthophosphate and sulfate on iron and arsenic removal will be determined. The
effect of water chemistry and oxidant on pilot plant operational parameters, such as filter headless, will also be
considered.
The results of this research thus far showed that (1) arsenic removal improves with increasing iron concentration and
particle surface area; (2) freshly precipitated Fe particles had a much greater capacity to remove arsenic than preformed
particles that were formed by oxidation of ferrous Fe with either oxygen or chlorine; (3) chlorination, or application of a
stronger oxidant, may be necessary to improve arsenic removal at many drinking water treatment plants; (4) the point
of strong oxidant addition in the treatment train is important; and (5) the pH and other competing water quality
variables such as phosphate play significant roles in the amount of arsenic removed.
EPA GOAL: Goal #2 - Clean & Safe Water; Objective 2.1.1- Water Safe to Drink
ORD MULTI YEAR PLAN: Drinking Water (DW), Long Term Goal - DW-2 Control, Manage, and Mitigate Health Risks
EXPECTED OUTCOMES AND IMPACTS:
The project will provide sound methods for improving and optimizing arsenic removal during iron removal to water
utilities, states, engineers, and consultants.
OUTPUTS:
Current outputs consist of several presentations and peer-reviewed journal articles.
• JOURNAL ARTICLE: Lytle, D.A., Sorg, T.J., and Snoeyink, V.L Optimizing Arsenic Removal During Iron Removal: Theoretical
and Practical Considerations. Journal of Water Supply: Research and Technology - AQUA 54(8):545-560, (2005).
International Water Supply Association (London, England). IWA Publishing, London, Uk.
RESOURCES:
EPA Arsenic Research: http://www.epa.Rov/nrmrl/wswrd/dw/arsenic/
Optimizing Arsenic Removal during Iron Removal: Theoretical and Practical Considerations:
http://www.iwaponline.com/iws/054/iws0540545.htm
NRMRL Drinking Water Research: http://www.epa.gov/ORD/NRMRL/wswrd/dw/index.html
NRMRL Corrosion Research: http://www.epa.gov/nrmrl/wswrd/cr/index.html
CONTACTS:
Darren Lytle, Principal Investigator - (513) 569-7432 or lytle.darren@epa.gov
Steven Doub, Media Relations - (513) 569-7503 ordoub.steven@epa.gov
Michelle Latham, Communications - (513) 569-7601 orlatham.michelle@epa.gov
National Risk Management Research Laboratory
Water Supply and Water Resources Division
www.epa.gov/nrmrl
EPA/600/F-10/005
February 2010
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