United States
Environmental Protection
Agency
Removal Technology
Activated Alumina (AA)
Uses a porous aluminum-based
material to adsorb certain
contaminants.
Anion Exchange
A physical-chemical process in
which ions are swapped between
a solution phase and a solid resin
phase. The solid resin adsorbs
anions and releases chloride into
the water.
Iron-Based Adsorptive Media
Uses an iron-based media to adsorb
contaminants.
Mixed Bed Ion Exchange
Anion and cation exchange resins
can be combined in a single ion
exchange unit to remove cationic
(e.g. radium) and anionic (e.g.
arsenic, uranium) contaminants.
Greensand Filtration
Uses manganese-coated filter
media to oxidize and adsorb
contaminants.
Oxidation/Coagulation/Filtration
Involves adsorption of contaminants
to an aluminum or ferric hydroxide
precipitate and removal of these
particles by filtration.
Lime Softening
Removes hardness by precipitating
out calcium and magnesium
carbonates.
Reverse Osmosis (RO)
A pressure-driven membrane
separation process that removes
contaminants larger than the
membrane pores.
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Removing Multiple Contaminants from
Drinking Water: Issues to Consider
Public water systems that need to add treatment for one contaminant may find that they also have other water quality
concerns. Choosing a treatment technology that can remove several co-occurring contaminants may be more efficient
and cost effective. This table describes treatment technologies that can remove multiple contaminants, identifies the
contaminants that can be removed, and summarizes related operational and waste disposal issues.
selenium
antimony
sulfate, magnesium,
calcium
iron, manganese (up
to 10ppm)
iron, manganese
hardness
TOC, most metals,
sulfate, calcium,
magnesium,
potassium,
phosphorous
Operational Issues
• Other ions may competitively adsorb and displace contaminant; AA is optimized at a pH of 6.0 to 6.5. pH 5.0-6.0 is optimal
for anion removal. Other ions, or removal of multiple ions will cause more frequent regeneration and require careful monitoring
to prevent breakthrough.
• When arsenic is present in the form As(lll), pre-oxidation is necessary to convert it to the form As(V).
• Must be backwashed periodically to prevent clogging.
• Must be periodically regenerated.
• System is low cost, easy to operate, and requires minimal operator attention.
pH of 6-8 in the treated water will maximize uranium removal and optimize resin regeneration. pH 6.5 to 9.0 is optimal for resins.
When arsenic is present in the form As(lll), pre-oxidation is necessary to convert it to the form As(V).
Uranium is the strongest binding contaminant, followed by arsenic and then nitrate. Uranium is so strongly adsorbed that it may
be difficult to regenerate the resin. Less strongly binding contaminants may breakthrough if not carefully monitored.
Sulfates, nitrates, and other ions compete for adsorption sites.
Total dissolved solids levels >500 mg/L can adversely affect treatment performance.
Pre-filtration is recommended if source water turbidity is >0.3 NTU.
Contaminant breakthrough can be avoided by careful monitoring and by running several columns in series, keeping the
most recently regenerated column last.
• Required operator skill level is intermediate.
• When arsenic is present in the form As(lll), pre-oxidation is necessary to convert it to the form As(V).
• Reducing source water pH will increase the arsenic removal capacity of most adsorptive media.
• If pH adjustment or pre-oxidation step is lost, treated water may have an arsenic spike.
• Phosphate and silica compete with As(V) for adsorption sites.
• Backwash is required to remove particulates and to redistribute media. Frequent or improper backwash can result in media loss.
• Bacteria can accumulate in the media during low flow and hot weather.
• When removing multiple contaminants the weaker adsorbing contaminant can breakthrough if not carefully monitored.
• System is low cost, easy to operate, and requires minimal operator attention.
• Optimum operating pH is >10.5 for radium removal and 6-10 for uranium.
• Sulfate and uranium can displace arsenic from the resin, causing a spike of arsenic in the treated water.
• Contaminant breakthrough can be avoided by careful monitoring and by running several columns in series, keeping the most recently regenerated column
last.
• May be necessary to increase treated water alkalinity after ion exchange to reduce corrosion in the distribution system.
• Intermediate operator skill level required.
• High iron to manganese ratio may lower radium adsorption on greensand filters, but the presence of iron is beneficial to arsenic adsorption.
• Arsenic removal by greensand requires a pH >6.8. Radium removal improves as pH increases over the range from 5 to 9.
• Minimal operator attention and maintenance requirements; required operator skill level is basic.
• Cost-effective for radium removal at small systems.
• When arsenic is present in the form As(lll), pre-oxidation is necessary to convert it to the form As(V).
• 20:1 iron to arsenic ratio will improve iron removal.
• Ferric chloride is typically used as the source of iron.
• Arsenic removal is less effective at higher pH.
• Operating costs are relatively low.
• Advanced operator skill level required.
• Optimum pH for Uranium removal is 6.0.
• pH >10 is needed for radium removal. Uranium removal requires pH >10.6 and is improved by adding magnesium carbonate.
• Advanced operator skill level required.
• Treatment costs are high and may not be a cost-effective alternative for small systems.
• It may be necessary to increase alkalinity for corrosion control.
• RO membranes foul easily, so pretreatment to remove particulates and organics may be necessary.
• Calcium and magnesium can cause membrane fouling.
• Cellulose acetate membranes are susceptible to biological fouling, free chlorine can be beneficial up to 1 mg/L.
• Polyamide membranes can be damaged by chlorine, high iron, and chloramines.
• Depending on operating parameters, 20 to 40% of raw water can be lost in the reject stream.
• Advanced operator skill level required.
• Treatment costs are higher than other treatment options.
Notes: Best Available Technologies (BATs) specified in regulations are indicated by /. Technologies that are effective but not currently listed as a BAT are indicated by 0.
Waste Disposal Issues
• Wastes include backwash water, brine, rinse water, and acid neutralization
water as well as spent filter media.
• Levels of arsenic and radionuclides will likely dictate options for spent
media disposal.
• Pretreatment may be needed for disposal to a sanitary sewer.
• Wastes include backwash water, regenerant brine, rinse water, and spent
media.
• Resins have a high capacity for absorbing arsenic, radium, and uranium
which will likely dictate options for spent media disposal.
• Pretreatment for spent brine may be needed for disposal to the sanitary
sewer.
Backwash water can be easily recycled through the treatment plant to
minimize waste generation, or it can be discharged to a sewer, septic
system, or surface water.
Testing is needed to ensure spent media is not hazardous or radioactive.
• Wastes include spent regenerate and spent media that may have elevated
concentrations of radium and arsenic which will dictate disposal methods.
• Pretreatment may be needed for disposal to the sanitary sewer.
• Wastes generated include sludge and supernatant from the filter
backwash as well as spent filter media. Radium and arsenic levels will
dictate disposal options.
• Wastes generated include iron and alum sludges from the contact and
settling basins, the supernatant from the sludge, filter backwash, and
spent filter media. Additional liquid waste may be generated when the
sludge is de-watered prior to landfill disposal.
• Backwash water is typically discharged to a sewage or septic system.
• High concentrations of uranium may dictate disposal options.
• Wastes include a high volume of lime sludge which precipitates with
radium and/or uranium, supernatant from the sludge, and filter backwash.
• Testing is needed to ensure spent media is not hazardous or radioactive.
• Wastes consist of concentrated waste stream and spent membranes
which may contain elevated levels of radionuclides.
• Testing is needed to ensure spent media is not hazardous or radioactive.
TIPS
More frequent monitoring
and shorter run times may
be necessary to prevent
breakthrough of weaker
absorbing contaminants for
certain technologies.
While a technology may
be able to remove multiple
contaminants, operating
parameters such as optimal
pH may vary for each
contaminant. Adjustments
may be necessary to maximize
treatment for the combined
contaminants.
In addition to cost, ease of
operations and operator
qualifications should be
considered.
Pre-oxidation may be
necessary for maximum
removal of certain
contaminants.
When considering treatment
efficacy, evaluate whether a
series or parallel configuration
will work best to prevent
breakthrough of contaminants.
Testing may be needed to
determine if spent media is
hazardous or radioactive.
If waste residuals contain
certain radionuclides such
as uranium or thorium, they
may be subject to the Nuclear
Regulatory Commission's
licensing requirements.
For more information:
EPA Office of Water Safewater site - http://www.epa.gov/safewater
EPA Office of Research and Development Drinking Water Research site - http://www.epa.gov/ord/dw/
Safe Drinking Water Hotline - 1 -800-426-4791
Office of Water
www.epa.gov/safewater
EPA816-H-07-004
December 2007
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