By: Arizona Water Quality Association
Arsenic occurs naturally in the environment as a heavy metal in two different
forms, arsenite (arsenic III) and
arsenate (arsenic V). Arsenic is released into water supplies from erosion of
rocks and soil. The distribution of arsenic in soil, groundwater and surface
water has extensively been investigated during the past two decades.
Long-term exposure to arsenic is proven to result in health
effects such as cancer, cardiovascular disease, diabetes and reproductive
problems. Nationally, about 3,000 (or 5.5 percent) of the nation's 54,000
community water systems and 1,100 (or 5.5 percent) of the 20,000 non-transient
non-community water systems will need to take measures to lower arsenic in
their drinking water. Of the affected systems, 97 percent serve fewer than
10,000 people. While high concentrations of arsenic are found mostly in the
Western region of the United States, parts of the Midwest and New England show
levels of arsenic
that exceed the newly approved U.S. Environmental Protection
Agency (EPA) standard of 10 parts per billion (ppb). The Western states have
more systems with arsenic levels greater than 10 ppb as compared to the
national average. Some systems in parts of the Midwest and New England have
current arsenic levels that are greater than 10 ppb, but most systems have
arsenic levels that range from 2 to 10 ppb of arsenic.
Treatment Options
During the EPA initial review of treatment options for
arsenic removal, ion exchange, activated alumina, reverse osmosis, enhanced
coagulation/filtration and oxidation/filtration were identified as best
available technologies (BAT). These technologies, along with other industry
emerging technologies, can be divided into three categories: sorption treatment
processes, membrane treatment processes and precipitation/filtration processes.
Through ion exchange (IX), arsenic is removed by
continuously passing water under pressure through column(s) packed with
exchange resin. As a low-cost treatment option when used under specific
operating criteria, IX has problems operating effectively with the presence of
high levels of sulfate (SO4-2) and total dissolved solids (TDS) in process
water.
Activated alumina (AA) is a porous, granular material with
properties similar to IX and commonly used for the removal of silica, natural
organic matter and fluoride. To remove arsenic using this process, water under
pressure is continuously passed through one or more beds of AA media. AA is pH
sensitive and its selectivity requires As III to be preoxidized, converting it
to As V before treatment. Currently, modified AA media are emerging to provide
drinking water systems with media that has greater overall adsorption
capacities, arsenic selectivity and operational flexibility than traditional
AA.
Reverse osmosis (RO), is an attractive treatment process
because it can address various water quality problems through a simple and
easy-to-use operation. RO is a pressure-driven membrane separation process that
removes dissolved solutes and greater than 90 percent of arsenic from water.
The RO treatment process is relatively insensitive to pH and has water recovery
rates ranging from 60 to 80 percent.
Enhanced coagulation/filtration, both conventional and
pressurized methods, can be used to remove inorganic arsenic from water. During
the treatment process, arsenic is adsorbed onto an aluminum, ferric hydroxide,
ferric sulfate or ferric chloride precipitate depending on application-specific
parameters. The economics and efficiency of this treatment system rely on
coagulant type and dosage, mixing frequency and pH levels. If optimized, this
treatment process can effectively remove greater than 90 percent of arsenic
from water.
Oxidation/filtration is a pressurized granular-media
filtration process that uses manganese-oxide media because of its adsorptive
and catalytic qualities. Under optimized conditions, this process and be a
cost-effective treatment option that yields an efficiency rate between 80 and
95 percent.
Granular ferric oxide/hydroxide media is an arsenic
treatment technology not initially included in the EPA's evaluation of
treatment processes. This adsorption process can be applied in fixed-bed
pressure column(s) similar to those for AA. Granular ferric oxide/hydroxide
media is not as pH sensitive as AA, can treat larger bed volumes and has higher
surface areas. Although this adsorption process has not been designated as a
BAT by the EPA, evaluation of the technology is underway.
Area of Concern
The EPA estimates that approximately 97 percent of community
water systems serving fewer than 10,000 people will be impacted by the 10 ppb
maximum contaminant level. This poses a problem, considering most small water
systems have small customer bases, few community assets and little income.
Funding to comply with the arsenic standard is available through the EPA's
drinking water state revolving fund (DWSRF). Capital projects that include new
technology and upgrading systems are eligible under the DWSRF. However, as one
might imagine, if a public water system applies for funding closer to the
compliance date of January 2006, the surge in applications coming in at that
time will impede the process to effectively meet all systems' needs.
Nonetheless, all systems will be required to comply with the
new standard, and consolidating or restructuring the water systems or using
point-of-use (POU) devices might be the most cost-effective options for these
small water systems.
Under the final EPA ruling, POU devices are approved as
small system compliance technologies (SSCT). SSCTs must be owned, controlled
and maintained by the public water system or by an agency under contract with
the water system (i.e., responsibility to operate and maintain these systems
cannot be passed along to the customer). While small system use of POU devices
will result in lower capital and treatment costs. Administrative and monitoring
costs will be higher. The EPA notes that previous studies show this to be an
economically viable treatment alternative for systems treating 50 to 250
people. Adsorption (AA or granular ferric oxide/hydroxide) and RO probably are
the industry's two most recognized treatment technologies for POU arsenic
removal. These technologies should be applied based on performance and cost for
effective arsenic removal.
What Dealers Should Know
Cost-effective and commercially proven arsenic removal
technologies currently are available to treat arsenic contamination.
Individuals not willing to wait for their water system's compliance with the
arsenic standard currently are looking for treatment systems to use in their
homes. POU and even point-of-entry (POE) treatment systems are an attractive
solution for these individuals. A water treatment dealer can address these
concerns by offering POU and POE systems for installation. The process should
begin with a basic understanding of arsenic contamination and the element's
chemistry, a complete water quality analysis of the application-specific water
and the knowledge of available technologies. When combined, water treatment
dealers then can present individual customers with the appropriate treatment
option for arsenic removal.
