United States
Environmental Protection
Agency
RESEARCH PROJECT
National Risk Management Research Laboratoi
Water Supply and Water Resources Division
Treatment Technology Evaluation Branch
THE ROLE OF MICROBIAL PROCESSES IN THE OXIDATION AND REMOVAL OF ARSENIC
FROM DRINKING WATER
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IMPACT STATEMENT
The U.S. Environmental Protection Agency (EPA) recently
reduced the drinking water standard for arsenic (As)
in water from 0.05 to 0.01 milligrams (mg)/Liter (L)
(10 micrograms (|ig) /L). This reduction was prompted by
new health effects research, which concluded that extended
human exposure to this element can cause severe illnesses
(including various types of cancers) at much lower levels
than previously believed. The recent revision to the arsenic
standard has required many new water treatment systems
to apply treatment processes. Findings from this study will
further enable EPA to provide subject matter expertise and
guidance on best available technologies for the removal of
arsenic from drinking water.
BACKGROUND:
The oxidation state of arsenic, As(lll) or As(V), is very important in water treatment, the latter can be removed more
easily. Source waters that contain As(lll) generally require the use of a strong oxidant such as free chlorine or
permanganate to oxidize the arsenic early in the treatment process. Oxygen is not an effective As(lll) oxidant, but it is
however, effective at oxidizing Fe(ll). Aeration is commonly incorporated into iron removal processes particularly in the
Midwest. For such systems that also contain As(lll) in their source water, they may need to add a stronger oxidant
before aeration to achieve the desired arsenic removal efficiency. The oxidation of As(lll) by bacteria is well known, but
never reported to be important in drinking water treatment systems. In water treatment, the application of microbial
processes is not a widely accepted practice in the United States. The lack of acceptance is due largely to the negative
perception of using bacteria to clean water when at the same time a goal of water treatment is to remove and kill
bacteria. Secondly, the concern that pathogenic bacteria could be harbored in the filters and regularly shed to the
finished water always exists.
One iron removal treatment plant (oxidation and filtration) in Ohio has observed effective iron (2.3 mg/L) and arsenic
(46 |ig/L) removal, and regularly meets the new arsenic standard. The majority of arsenic in the raw water is in the
reduced As (III) form (37 |ig/L). The interesting observation is that arsenic is removed without the addition of a strong
chemical oxidant such as free chlorine to convert As (III) to the more easily removable As (V) form. Aeration is used to
oxidize iron in the source water. Preliminary investigations suggested that oxidation of As (III) takes place within the
filters by microorganisms which could explain the greater than expected arsenic removal. If microbiological oxidation of
As (III) does occur within the filters, taking advantage of the natural microbiological population in the source water can
avoid the need, costs, and possible complications associated with adding a strong oxidant to the water.
National Risk Management Research Laboratory
Water Supply and Water Resources Division
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DESCRIPTION:
The objectives of this study were to 1) document the removal of arsenic in a full-scale water treatment plant, 2) conduct
bench-scale studies to identify the mechanism(s) responsible for arsenic removal, 3) identify the role of bacteria, if any,
on arsenic removal, and 4) conduct pilot-scale studies to identify the most effective and rapid method to regain
microbial activity within the filters.
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:
Water utilities, states and engineers will better understand nitrification problems and approaches to reduce nitrification in
distribution systems.
OUTPUTS:
Current and future outputs of the project will consist of published papers, peer-reviewed journal articles.
RESOURCES:
EPA Arsenic Research: http://www.epa.Rov/nrmrl/wswrd/dw/arsenic/
NRMRL Drinking Water Research: http://www.epa.Rov/ORD/NRMRL/wswrd/dw/index.html
NRMRL Treatment Technology Evaluation Branch: http://www.epa.ROv/ORD/NRMRL/wswrd/tteb.htm
CONTACTS:
Darren Lytle, Principal Investigator - (513) 569-7432 or lytle.darren@epa. gov
Steven Doub, MediaRelations - (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-10/008
February 2010
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