United States
Environmental Protection
Agency
RESEARCH PROJECT
National Risk Management Research Laboratoi
Water Supply and Water Resources Division
Treatment Technology Evaluation Branch
RELATIONSHIP BETWEEN REDOX POTENTIAL, DISINFECTANT, AND pH IN DRINKING WATER
IMPACT STATEMENT
Oxidation-reduction (redox) reactions control many
chemical and biochemical processes in both nature and
engineered systems, such as water treatment processes.
Measuring oxidation-reduction potential (ORP) in water is
a well-established method used to indicate the redox
reactions of water. ORP readings can provide water utility
operators with beneficial water quality information such
as the effectiveness of disinfectant and microorganism
kill rates. Despite the availability of this technology, ORP
measurements are not widely made by drinking water
utilities for numerous reasons, including electrode
reliability issues and, most importantly, the lack of
understanding of what these measurements actually
represent in a natural water system. Very little research
has been conducted to understand the effect of pH,
oxidant type, and oxidant concentration on ORP. This study will further contribute to on-going investigations by the U.S.
Environmental Protection Agency (EPA) to develop predictive and preventative tools for monitoring drinking water
processes. In doing so, this study will position EPA to continue providing subject-matter expertise and guidance to
drinking water utilities, engineers, the general public and other stakeholders.
BACKGROUND:
Because redox reactions describe chemical and biological systems, they are especially important to drinking water
treatment. In water, examples of naturally occurring reductants include iron2+and Manganese2*. Common oxidants
used in drinking water treatment for microbial disinfection and oxidation of inorganic and organic contaminants include
free chlorine (HOCI and OCI-1), oxygen, monochloramine, and ozone. Furthermore, the type and amount of reductants
and oxidants present in a water system directly impact the ORP, and can greatly change the water quality of an aqueous
system. Eh-pH diagrams can predict how redox conditions and pH impact the chemistry of aqueous species. These
diagrams are derived from fundamental chemistry relationships and experimentally developed parameters, and they are
well accepted and frequently used by engineers and scientists. ORP values listed in Eh-pH diagrams correspond to the
theoretical Eh.
Despite the amount of research dedicated to ORP measurement accuracy and usable monitoring devices, established
ORP ranges for common oxidants still remain unknown. Determining expected ranges and then comparing them to real
field measurements may be advantageous to prove ORP measurements are viable, and could be used to identify
problems with drinking water treatment.
DESCRIPTION:
This work will examine the effects of pH and oxidant type (chlorine [CI2], oxygen [O2], hydrogen peroxide [H2O2],
monochloramine [MCA], and potassium permanganate [KMnO4]) and concentration (mg/L) on the redox potential of
National Risk Management Research Laboratory
Water Supply and Water Resources Division
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buffered test water. Also, the effects of incrementing iron with each oxidant will be investigated. The consistency and
uncertainty of redox potential electrodes will also be explored. Using these associations, this research aims to achieve
concrete relationships between redox potential, pH, and dose for each oxidant.
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:
After determining the actual relationships between redox potential, pH, and dose for each of the subject oxidants, the
findings can be transferred to utility, engineering, consulting and other clients and stakeholders to optimize system
performance with specific oxidant types.
OUTPUTS:
An output of the project will consist of a journal article.
RESOURCES:
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
NRMRL Treatment Technology Evaluation Branch: http://www.epa.gov/ORD/NRMRL/wswrd/tteb.htm
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-10/006
February 2010
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