Arsenic Removal - I2M Associates, LLC
Arsenic Removal: Lessons Learned Since 2002 By Lee Odell, Water Treatment Global Technology Lead, CH2M HILL, and Sam Perry, Water Treatment Engineer, Washington State Department of Health
Introduction In the United States, arsenic has been regulated in drinking water since 1942, when a standard of 50 ug/L was set. In 1962, the US Public Health Service recommended lowering the drinking water standard to 10 ug/L, but it wasn’t until 2001 when the U.S. Environmental Protection Agency (EPA) promulgated the final arsenic primary drinking water maximum contaminant level (MCL) of 10 ug/L that became effective February 22, 2002. Since that time many research projects, health effects studies, and deployments of new technologies have been completed. The purpose of this article is to try to summarize the key findings from the last 10 years of industry work on arsenic removal. Arsenic Occurrence Arsenic is found in groundwater sporadically throughout the United States, as shown in Figure 1, from the U.S. Department of the Interior (Fact Sheet FS-063-00).
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Arsenic is found in surface water and groundwater as a result of natural processes such as the weathering of minerals and microbial activities. Major anthropogenic sources include mining, particularly smelting, and pesticide manufacture and use. A variety of industries also use arsenic compounds in their production processes. Generally, naturally occurring arsenic concentrations are below 1 ug/L. Higher concentrations are found in localized zones of contamination. Inorganic forms of arsenic are most common, although organic arsenic compounds associated with microbial activity and pesticide manufacture do occur. Significant concentrations of organic arsenic are generally not found in groundwater used for drinking water supply. Aqueous, inorganic arsenic can exist in four valence states: As+5, As+3, As, and As-3. Only As+5 (also referred to as As(V), or arsenate) and As+3 (referred to as As(III), or arsenite) are relevant for drinking water treatment. Speciation is dependent on pH and redox conditions. Oxidizing environments tend to produce arsenate forms; arsenite is produced in acidic-reducing environments. Distribution diagrams for As(III) and As(V) as a function of pH indicate that arsenite is present primarily as the undissociated acid, H3AsO3, below pH 9. As(V) is present primarily as HAsO42- at pH values above 7; H2AsO- 4 predominates below pH 7. Arsenic Health Effects Updates The primary health concerns from chronic low-level arsenic exposure cited in the development of the Arsenic Rule were carcinogenic (bladder, kidney, lung, and skin). However, the permeable to the Arsenic Rule also cited other health concerns associated with chronic low-level exposure including diabetes and cardiovascular diseases. With regard to the carcinogenic effects, the EPA indicated in 2001 that the long term health effects studies were not complete, and that they would have to decide in 2007, when they were scheduled to be complete, whether or not a new rule would have to be developed. In 2007, the EPA completed a draft arsenic health effects assessment report, which was reviewed twice by the Science Advisory Board and was released in October 2010 as an external review draft. The 2010 report identified the arsenic cancer risk as 17 times higher than previously thought. The report was criticized and on January 9, 2013, the EPA announced that the agency will scrap its 2010 draft assessment of arsenic under the Integrated Risk Information System (IRIS) program and develop a new review. In the past 10 years, there have also been a number of studies released on the non-carcinogenic effects of arsenic exposure. One of the most high profile studies indicated that the risk of type 2 diabetes from inorganic arsenic was significantly greater than previously thought (Navas-Acien, et.al, 2008). After analyzing 788 U.S. adults aged 20 or older, the research indicated that people with type 2 diabetes had a 26% higher level of total arsenic in their urine than participants without type 2 diabetes. People with the highest levels of arsenic exposure in the study were almost 3.6 times more likely to have diabetes than people with the lowest levels. An even larger study was released in 2011 on the cardiovascular effects of arsenic (Chen et al, 2011). In this study, more than 11,000 participants were tracked for almost 7 years to ascertain the increased cardiovascular risk of inorganic arsenic exposure in drinking water. The study indicated a strong doseresponse relationship between arsenic exposure and increased risk of heart attacks at levels of exposure just slightly above the current MCL (Figure 2). For example, people who used wells with total inorganic arsenic in the 12-62 ug/L range had a 22% increased risk of death from a heart attack than people who used wells with less arsenic (7.5 at 20 mg/L and 50 mg/L regardless of pH. Forms complexes on surface of adsorbent media leading to poor arsenic adsorption. Inhibits formation of iron floc that can be filtered.
Vanadium
Similar to arsenate and competes for binding sites on ion exchange and other adsorptive media. Concentrations in raw water are typically low (
Introduction In the United States, arsenic has been regulated in drinking water since 1942, when a standard of 50 ug/L was set. In 1962, the US Public Health Service recommended lowering the drinking water standard to 10 ug/L, but it wasn’t until 2001 when the U.S. Environmental Protection Agency (EPA) promulgated the final arsenic primary drinking water maximum contaminant level (MCL) of 10 ug/L that became effective February 22, 2002. Since that time many research projects, health effects studies, and deployments of new technologies have been completed. The purpose of this article is to try to summarize the key findings from the last 10 years of industry work on arsenic removal. Arsenic Occurrence Arsenic is found in groundwater sporadically throughout the United States, as shown in Figure 1, from the U.S. Department of the Interior (Fact Sheet FS-063-00).
1/12
Arsenic is found in surface water and groundwater as a result of natural processes such as the weathering of minerals and microbial activities. Major anthropogenic sources include mining, particularly smelting, and pesticide manufacture and use. A variety of industries also use arsenic compounds in their production processes. Generally, naturally occurring arsenic concentrations are below 1 ug/L. Higher concentrations are found in localized zones of contamination. Inorganic forms of arsenic are most common, although organic arsenic compounds associated with microbial activity and pesticide manufacture do occur. Significant concentrations of organic arsenic are generally not found in groundwater used for drinking water supply. Aqueous, inorganic arsenic can exist in four valence states: As+5, As+3, As, and As-3. Only As+5 (also referred to as As(V), or arsenate) and As+3 (referred to as As(III), or arsenite) are relevant for drinking water treatment. Speciation is dependent on pH and redox conditions. Oxidizing environments tend to produce arsenate forms; arsenite is produced in acidic-reducing environments. Distribution diagrams for As(III) and As(V) as a function of pH indicate that arsenite is present primarily as the undissociated acid, H3AsO3, below pH 9. As(V) is present primarily as HAsO42- at pH values above 7; H2AsO- 4 predominates below pH 7. Arsenic Health Effects Updates The primary health concerns from chronic low-level arsenic exposure cited in the development of the Arsenic Rule were carcinogenic (bladder, kidney, lung, and skin). However, the permeable to the Arsenic Rule also cited other health concerns associated with chronic low-level exposure including diabetes and cardiovascular diseases. With regard to the carcinogenic effects, the EPA indicated in 2001 that the long term health effects studies were not complete, and that they would have to decide in 2007, when they were scheduled to be complete, whether or not a new rule would have to be developed. In 2007, the EPA completed a draft arsenic health effects assessment report, which was reviewed twice by the Science Advisory Board and was released in October 2010 as an external review draft. The 2010 report identified the arsenic cancer risk as 17 times higher than previously thought. The report was criticized and on January 9, 2013, the EPA announced that the agency will scrap its 2010 draft assessment of arsenic under the Integrated Risk Information System (IRIS) program and develop a new review. In the past 10 years, there have also been a number of studies released on the non-carcinogenic effects of arsenic exposure. One of the most high profile studies indicated that the risk of type 2 diabetes from inorganic arsenic was significantly greater than previously thought (Navas-Acien, et.al, 2008). After analyzing 788 U.S. adults aged 20 or older, the research indicated that people with type 2 diabetes had a 26% higher level of total arsenic in their urine than participants without type 2 diabetes. People with the highest levels of arsenic exposure in the study were almost 3.6 times more likely to have diabetes than people with the lowest levels. An even larger study was released in 2011 on the cardiovascular effects of arsenic (Chen et al, 2011). In this study, more than 11,000 participants were tracked for almost 7 years to ascertain the increased cardiovascular risk of inorganic arsenic exposure in drinking water. The study indicated a strong doseresponse relationship between arsenic exposure and increased risk of heart attacks at levels of exposure just slightly above the current MCL (Figure 2). For example, people who used wells with total inorganic arsenic in the 12-62 ug/L range had a 22% increased risk of death from a heart attack than people who used wells with less arsenic (7.5 at 20 mg/L and 50 mg/L regardless of pH. Forms complexes on surface of adsorbent media leading to poor arsenic adsorption. Inhibits formation of iron floc that can be filtered.
Vanadium
Similar to arsenate and competes for binding sites on ion exchange and other adsorptive media. Concentrations in raw water are typically low (
