The Board of Directors of Plumbing Manufacturers Intl. (PMI) voted to...
Arsenic Treatment for Small Public Water Systems
Fueled by a rapidly approaching deadline to comply with
stringent U.S. Environmental Protection Agency (EPA) rules for arsenic in
public drinking water, emerging commercial technologies are replacing the
"old standards" for small water system (SWS) applications. Within the
categories of small community and non-community, non-transient systems, the
highest percentage requiring treatment are those with populations of 25 to 500.
(See Table 1.) Distinctive needs of these SWS projects in contrast to large
community systems dictate that competitive economics, simple operation and low
waste production will drive changes in technology and engineering. Some
out-of-the-box thinking will be necessary in the shift to provide simpler,
packaged or preengineered arsenic treatment systems. These developments will
unintentionally alter the traditional role of the engineer by offering more
efficient time use for planning and project implementation by including the vendor
and EPA as partners in the decision-making process.
EPA mandated reductions to a maximum contaminant level (MCL)
of 10 parts per billion (ppb) arsenic by Jan. 23, 2006, are disproportionately affecting
these small and very small systems. Inadequate financial and engineering
resources, limited equipment space and local technical operators dictate using
the simplest treatment systems possible. Table 2 summarizes some of the
challenges faced by smaller systems as they gear up for compliance with the
For smaller systems, more costly traditional methods of
treatment must be supplanted by or, in some cases, coupled with new techniques
to provide more affordable, flexible and easily implemented treatment systems
with a high degree of reliability. Treatment methods and engineering
traditionally have been geared towards systems serving more than 10,000 people.
Large municipal systems with greater funding options are capable of designing and
operating more complex processes such as reverse osmosis, electrodialysis, ion
exchange or coagulation/filtration. Small systems, however, face unique issues
that have created momentum in the direction of adsorption-based treatment
technologies. Difficulty in obtaining funding means that engineering time and
capital expenditures must be optimized, giving preengineered systems a
measurable advantage. Engineering efforts then can concentrate on plan
preparation and construction.
EPA recognized this need and has responded. Treatment
demonstrations are underway to expand best demonstrated available technologies
(BDAT), which may be considered by the small system owners. New
adsorption-based technology is at the forefront of those replacing conventional
BDAT options. As proof of the major role adsorption will play as a dominant
treatment category, EPA has chosen adsorption methods for nine of the 12
demonstration sites around the United States. Preliminary results for selected
sites will be available beginning in first-quarter 2004.
Multiple benefits are realized with an adsorption system.
Although several types of adsorption technology have been developed, iron-based
media are leading the pack. Using media that are capable of addressing both
arsenic III and V at normal pH ranges (5.5 to 8.5) reduces costs of
pretreatment and operator involvement since no pH adjustment or media
regeneration are required. For example, advantages of using an adsorption
process such as granular ferric oxide (GFO) include
reducing arsenic III and V without a preoxidation step.
ratings of up to 99 percent removal to treat arsenic less than 2 ppb.
over varied water chemistry.
no high pressure pumps.
low energy consumption.
of preengineered modular units.
integrated into any system.
[if !supportEmptyParas] [endif]
Arsenic specificity and efficiency
style='font-weight:normal'>. High efficiency adsorption can effectively reduce
arsenic to less than 2 ppb, achieving the required MCL while also reducing
other inorganic co-contaminants (i.e., Pb, Sb, Se, V, Mo) present in ppb
concentrations. Some iron-based adsorbents also can effectively reduce both
forms of naturally occurring arsenic without pretreatment (oxidation), which
saves considerable capital and operating expenses. The treatment process does
not alter the overall chemical composition of the water being treated. No other
ions are exchanged into the potable water supply.
Low pressure requirements
normal'>. While adsorption systems frequently are housed in ANSI-rated or other
pressure vessels, they can operate under gravity flow. Head loss across the
media bed is less than 5 psi.
Minimal energy requirements
normal'>. As there are no high pressure pumps or other high energy consumption
operations, adsorption most often will have the lowest operating cost as
compared to other technologies.
Low water consumption.
Adsorption media (which are not regenerated) do not create a concentrated brine
or hazardous waste residual that must be disposed of since no regeneration step
is required. Other technologies can waste valuable water resources, in some
case as much as 75 percent.
Adsorption systems that are preengineered be easily can integrated into
existing operations. Equipment compatibility is ensured and products are used
that have third-party certifications (e.g., ANSI/NSF International standards)
for use in potable water. Low head loss, low energy requirements and chemical
stability allow systems to be placed in-line at any point allowed by
operational convenience. Due to low pressure requirements, preengineered units
can be installed at the well head, down stream of pressure or atmospheric
storage tanks and even downstream of chlorination.
Simple to operate.
Iron-based adsorption systems eliminate the need for intensive operator
attention and maintenance. In fact, systems consist of simple, down-flow packed
beds that require only weekly inspection and periodic backwashing to eliminate
grit and fines that may originate in the well. No extensive operator training
Finally, permitting is more streamlined when preengineered
vendor submittal packages are included as technical validation. Regulatory
control is satisfied as application processing is made simpler.
Achieving these goals requires the coordinated efforts of
the local water supply company or system, regulators, consulting engineers, and
vendors. The job of providing a reliable and affordable supply of clean water
falls to the small water system owner/operator. Consulting engineers represent
the interests of the SWS and ultimately, the rate-payer. Often the engineer
acts as the focal point and must interpret the regulations, audit the existing
distribution system, evaluate commercially available technologies, and
recommend the most cost effective strategy.
Packaged, pre-engineered systems reduce the long learning
curve for those who must select and implement a strategy from the vast array of
arsenic treatment options and efficiencies. The result is better cost options
for the water system and more effective time utilization for the engineer.
Vendors having strong technical expertise are able to work closely with
consulting engineers and regulators whose approval must be gained in order to
A partnership between the small water system, engineer and
vendor benefits all parties with ease of implementation. Table 3 presents a
flow chart of a traditional engineering approach compared to a more rapid or
streamlined approach that may become more prevalent for arsenic treatment
utilizing packaged adsorption systems. Duplicate efforts are avoided and costs
reduced for the end user. This cost control may tip the balance between
compliance and bankruptcy for the SWS. At a minimum, it will reduce time,
money, and perhaps ease the pain of the process.
Engineers are finding that adsorption systems better serve
their customer, the SWS. With simpler equipment and operations, process selection
is faster. Less detailed engineering is required because "plug and
play" arsenic adsorption systems are compatible with a variety of existing
Because EPA demonstrations to validate technologies as BDAT are
national in scope, work is shifting from less piloting and study phases to
greater emphasis on implementation. These evaluations also will streamline the
decision tree or selection process and provide confidence that is directly
translatable into cost savings for the small water system.
At the end of the day, success for the SWS will be judged by
meeting the new MCL and other desired performance objectives and satisfaction
of the end user and individual rate-payer. Yes, providing safer drinking water
ultimately will impact the pocket books of the end users. The arsenic rule is
no exception. However, the outcome can be a win-win for the parties if the
success criteria are met. These criteria are easy to understand, but more challenging
New commercial adsorption technologies are forging an
encouraging pathway for what normally would be considered an intimidating, if
not daunting, task of complying with the new arsenic rule. Like the best
available technologies, roles of the parties involved are changing as well to
adapt to the special needs of small systems, who are under-resourced and in
need of help. With all the regulatory developments, education, training and
media coverage over the past two years, there clearly is an unparalleled
awareness. However, education gaps still remain to be filled. The irony is that
the facilities (systems) that will be impacted the most are the ones with the
least access to financial resources and assistance. It will take some
out-of-the-box actions by all parties to meet the special needs of these small
utilities and public water systems as they navigate through these challenging waters. style='mso-tab-count:1'>