Current Solutions and Practices
EPA has indicated that the original compliance date of June 22, 2006, will
be maintained, giving utilities up to five years to meet the final standard.
Consumers unwilling to drink arsenic contaminated water are demanding a more
rapid implementation. Publicly owned utilities, however, will be held hostage
from implementing a more rapid solution due to government approval cycles,
annual budgets, required biding processes and slow implementation schedules. As
a result, in-home treatment systems, which immediately can be installed, are a
very popular treatment option for individual homeowners. Other advantages such
as low implementation/operating costs and improved flexibility make the POU/POE
approach option appealing.
For small communities with centrally treated water, the POU approach, also
is growing in appeal. EPA’s most recent task force on implementation costs now
estimates that for small communities with less than 5,000 homes, the POU option
may be the most affordable approach. Disadvantages for the POU approach in
compliance situations include unawareness of certain source water conditions,
proper access into the home for installation and maintenance, effective
performance monitoring, compliance sampling, and proper record keeping of
compliance testing and certification.
For communities larger than this, centrally treated water remains the most
economical approach.
POU/POE Treatment options
The top two POU/POE treatment technologies recognized by the industry are
adsorption and reverse osmosis. The table below highlights the advantages and
challenges faced by each technology.
Submit POU/POE Treatment Options
|
Treatment Technology |
Technology Description |
Advantages |
Challenges |
|
Adsorption |
Filtration media that chemically binds the arsenic to the adsorbent. · Activated Alumina · Mixed Metal Oxides · Granular Ferric Hydroxide |
· No wasted water · Removal of both As (III) and (V) · Removal of other heavy metals such as
flouride, copper, etc. · Safe handling and disposal. · Spent media meets EPA TCLP · Low cost option · No chemicals or regeneration required |
· Requires certain contact time for optimal
effectiveness · Competing ions in water can reduce
capacity · Performance decreases with higher pH |
|
Reverse Osmosis |
Water is forced under pressure against a semipermeable membrane creating a
barrier between the clean water and the contaminants of concern. |
· Effectively reduces arsenic (V) · Provides high quality drinking water,
removing other dissolved contaminants · Improves taste/odor, aesthetics · Arsenic (V) removal efficiency |
· Not effective for As (III) without
preoxidation · High cost if arsenic is primary target
contaminant · Not suitable for POE systems due to corrosion
and affordability · Requires proper attention and routine
maintenance · Wastes 3-5 gallons of water for every
treated gallon |
Immediate protection from contaminated water. An abundance of water treatment
professionals are available to assist in selecting an appropriate system to
meet specific treatment and maintenance needs.
Simple maintenance, usually performed by the homeowner through
cartridge replacement. Waste disposal of adsorption technologies are non
hazardous and can be disposed with household waste
Lower cost. At $0.10 to $0.20/gal., POU treated water is more than 50
percent less than the cost of bottled water, which ranges from $0.75 to $2/gal.
Initial capital costs range between $250-500. Annual operating and maintenance
costs will average $30-50. Annual costs are minimized because only the water
needed for consumption is treated.
Customized flexibility. POU systems can be custom designed, allowing
the consumer the opportunity to address a range of concerns based on budget and
preferences. It also creates flexibility to cost effectively upgrade the system
should new cartridge-based improvements be commercialized. The customer has the
choice to decide which aspects of his water are most important to him and focus
a solution towards improving the quality of his drinking water based on his
needs and budget.
What level of arsenic is in the water? This factor will help
determine the effectiveness of the system as well as the level of required
maintenance.
What form of arsenic is in my water? Arsenic comes in both a
pentavalent (AsV) and a trivalent (As III) state. Arsenic (III) is the harder
to remove and more hazardous of the two. Not all treatment systems can remove
both forms of arsenic and convert it to As (V) through oxidation with chemicals
such as chlorine, potassium permanganate or ferric chloride, which can be
dangerous to humans.
What is the water profile? Several characteristics of the water such
as pH silicate level and temperature can effect the performance of a treatment
system being considered, which may also make a pretreatment system necessary.
This question is important for a small community system interested in using a
POU solution for compliance.
How much water will be treated? Do I want to treat all of the water
in my household or just my drinking water? This decision greatly will impact
the cost of the treatment system. EPA data indicates that arsenic only is
dangerous when ingested through consumption.
What type of waste is generated by the treatment system? Is there
water waste? Is a hazardous material generated? Is disposal of the waste a
problem?
How do I test for arsenic? There are several field test kit systems
that can be used to determine the level of total arsenic present in the water.
The use of these tests kits can help determine the level of treatment needed
and ensure proper function of the treatment system once installed.
Treatment options for
central treatment systems
For communities serving greater than 5,000 homes, central treatment has been
identified as the most cost effective approach. Typical central treatment
technologies used for arsenic reduction include coagulation/filtration, lime
softening and ion exchange.
Submit Central Treatment System Options
|
Treatment Technology |
Description |
Advantages |
Challenges |
|
Coagulation / Filtration |
Coagulants added to the influent water change the surface properties of suspended
solids to allow agglomeration of particles into a flocculated precipitate
that is filtered out. |
· Easy modification of existing system can
be performed to increase arsenic removal · 95% removal of As (V) |
· Not effective for As (III) without
preoxidation · Performance decreases with higher and
lower pH · Arsenic contaminated coagulation sludge
may present a disposal issue · Requires well-trained operators |
|
Lime Softening |
Cold Lime-softening: The process wherein lime is added to cold water,
usually along with a small amount of coagulant and the reaction causes
bicarbonate alkalinity to precipitate as calcium carbonate. Process used
mainly in municipal systems for partial hardness reduction. See also Cold
Lime-Soda Softening. |