Using Advanced Adsorptive Media for Arsenic Treatment

March 28, 2002
New POU Technologies May Be the Answer for Small Municipalities Facing High Costs

About the author: Greg Gilles is vice president of technical services and Jennifer Mathis is a sales representative for Apyron Technologies, an Atlanta-based material science company developing advanced solutions for arsenic treatment.

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On November 26, 2001, the new arsenic standard was signed into law—lowering the acceptable level for the contaminant from 50 parts per billion (ppb) to 10 ppb. Approximately 4,100 municipal water systems serving nearly 13 million people nationwide are affected by the law and are required to meet compliance by January 2006. According to the U.S. Environmental Protection Agency (EPA), 97 percent of these systems are small systems serving fewer than 10,000 people each. The economic impact on these small systems is likely to be large. However, there currently are options available to small municipalities that may be more affordable than central treatment.

Prior to the ruling on the arsenic standard, the EPA commissioned three reports: the Arsenic Rule Benefits Analysis by the Science Advisory Board, the Health Effects Study by the National Academy of Sciences and the Cost Review Report by the National Drinking Water Advisory Council (NDWAC). The results of these three reports prompted the EPA to finalize a new standard after more than 20 years of debate. (See EPA’s web site—www.epa.gov—for the full reports and see the February article in WEM, “Arsenic in Drinking Water—The Development of Drinking Water Regulations,” by John T. O’Connor.)

In the cost review report, NDWAC recommended that small municipal systems serving up to 10,000 people give greater consideration to implementing point-of-use (POU) treatment technologies instead of centralized treatment. In response to this recommendation, the EPA Office of Ground Water and Drinking Water awarded a grant to NSF International in December 2001 to conduct a POU demonstration project. This project will pair a small public water system with solution providers in order to develop and test a program that examines each step of a cost-effective POU strategy for compliance with the new arsenic standard.

For some small municipalities, implementing a centralized treatment system likely will prove to be complex, cost-prohibitive and quite challenging given the lack of technical expertise and resources. POU may be a more cost-effective method to meet compliance with the new law, particularly for those systems serving fewer than 3,300 people. A critical success factor for community-wide POU applications will be the ability to implement a technology that has demonstrated capability in POU arsenic removal.

Flexibility, Simplicity and Effectiveness

Small municipalities that choose to implement POU technology for compliance with the new arsenic standard most likely will use adsorptive media or reverse osmosis (RO) treatment options. These options are considered to be Best Available Technologies (BAT) by EPA. An important issue for arsenic removal is the understanding of arsenic speciation and its effects on selected technologies. Arsenite (Arsenic III), as an uncharged species, often co-exists with the oxidized form, arsenate (Arsenic V), in water. Both forms are present in many public and private groundwater or well water supplies in the United States, as documented by the EPA and others.

RO systems are widely used in the United States for various water purification functions. They remove 85 to 95 percent of Arsenic V, as well as other contaminants, from drinking water. However, RO systems have limited capability to remove Arsenic III from water, the more harmful and difficult to remove of the two forms. Since many small community and non-transient systems have no form of disinfection or chemical oxidation, indiscriminate use of RO systems leaves the possibility of inadequate arsenic treatment.

To effectively remove all forms of arsenic, new advanced adsorptive medias (such as Apyron Technologies’ Aqua-Bind) should be considered. Advanced adsorptive media remove up to 99 percent of both forms of arsenic from drinking water. These media can be used independently or in conjunction with other treatment systems, like RO. 

Successfully operating in more than 200 systems across the United States, adsorptive arsenic removal media have demonstrated the operating flexibility, simplicity and effectiveness required for use in POU applications. These successful results point to a logical next step—employing adsorptive media POU technologies in compliance strategies for small municipalities. Apyron intends to participate in the EPA-sponsored project that will develop and test POU compliance for small public systems.

The flexibility of adsorptive media enables it to tackle extreme arsenic levels such as those experienced in the northeast corridor of the United States (Table 1). The technology’s flexibility stems from its ability to

               Operate under a wide range of influent water chemistry,

               Remove both Arsenic III and V, and

               Treat high arsenic levels to below detection level (BDL).

Additional benefits of the system include reduction of heavy metal contaminants such as lead, copper, zinc, fluoride, selenium and antimony as well as improved taste and odor.

An added feature of the medium is that it is available in a variety of standard- and custom-sized cartridges. The product package can be modified to fit specific space and system configurations, enhancing the cost-efficiency and flexibility of the system. The cartridges also can be custom-designed based on specific water characteristics and applications.

A wide range of arsenic concentrations is treated with cartridges in one of three size configurations: 2.5* ¥ 10*, 4.5* ¥ 10* and 4.5* ¥ 20*, used in standard pressure-rated housings. The cartridges can be used as a stand-alone treatment system or as an addition to filtration already in place such as an RO system. The 2.5* ¥ 10* cartridge is a cost-effective and efficient post-RO addition, removing the Arsenic III left behind by the RO system.

Figure 1 illustrates the effectiveness of a standard 10* adsorptive media cartridge installed immediately after a conventional under-counter RO system. An average of 40 ppb Arsenic III influent solution was maintained in the absence of dissolved oxygen for the experiment.

A homeowner in Bow, N.H., can attest to the effectiveness of the RO/POU adsorptive media cartridge. He contacted a local water professional after testing his well and finding arsenic at 520 ppb. The water professional installed an RO system followed by an adsorptive media cartridge for the removal of both forms of arsenic. The system has successfully treated approximately 180–220 gallons effectively to below the detection limit of 5 ppb for the past four months.

Another key benefit associated with use of advanced adsorptive media cartridges is the longevity of the media life in atypical conditions. A homeowner in Northport, Maine, tested his drinking water and found that his well had arsenic levels greater than 970 ppb. He contacted a water professional who assisted him in custom designing a POU system using twin adsorptive media cartridges. Two 3* ¥ 40* cartridges were installed in series with a .25 gpm flow rate to treat 1–2 gallons of water per day for potable use. The treatment system was installed in March 2001 and has successfully treated approximately 287 gallons of water to below 5 ppb.

The Case for POU In Municipal Compliance

Homeowners commonly use POU technologies to reduce hardness, remove heavy metals and improve taste and odor of their drinking water. However, public or private utility use of a point-of-use/point-of-entry(POU/POE) solution to meet an enforceable drinking water standard is a fairly new approach. In 1996, the Safe Drinking Water Amendments allowed utilities to consider the use of POU/POE technology to meet compliance with various enforceable standards. Now, the EPA is required to consider POU/POE devices as potentially affordable means of achieving compliance, particularly for small municipal systems.

The EPA has investigated cost, performance and management issues associated with POU/POE in compliance situations. In 30 case studies, the agency found that POU/POE can offer an affordable and executable option to meet drinking water standards and that consumers accept in-home access required to ensure that systems are properly installed, maintained and monitored for performance. The EPA previously estimated 4 to 5 percent of small water systems (less than 500 customers) would use POU for compliance. Now, with new evidence from the National Drinking Water Advisory Committee’s Arsenic Cost Work Group, the percentage is significantly higher.

It is difficult to determine a precise cost estimate for compliance with the new arsenic standard because each of the 4,100 affected systems has unique circumstances and water profiles. The NDWAC’s report concluded that the EPA’s original annual cost estimate of $195 million, which focuses primarily on central treatment, is most likely accurate. However, other studies, such as one conducted by the American Water Works Association Research Foundation (AWWARF), claim that the national cost will be much higher—in the $400 million-per-year range.

Both groups are in agreement that centralized treatment for small and very small systems is more costly per capita and could be two to five times the monthly cost compared to larger systems. POU may enable a lower cost option for many small municipalities. At $.10 to $.20 per gallon, POU treated water is more than 50 percent less costly than bottled water, which ranges from $.75 to $2.00 per gallon. Initial capital costs including installation of an adsorption-based POU system in a single home can range between $150 and $200. Annual costs thereafter are reduced to the cost of replacement cartridges, from $60 to $150.

Of course, there are a number of other compelling reasons small municipalities should consider POU-based treatment options such as proven performance, simplicity of operation and reliability. Although implementing POU technology community-wide is a relatively new approach to meet compliance, small municipalities owe it to their citizens, who will bear the cost, to investigate all options.

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