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The Removal of Ammonia, Arsenic, Iron and Manganese by Biological Treatment from a Small Iowa Drinking Water System
Citation:
Lytle, D., D. Williams, C. Muhlen, E. Riddick, AND M. Pham. The Removal of Ammonia, Arsenic, Iron and Manganese by Biological Treatment from a Small Iowa Drinking Water System. Environmental Science: Water Research & Technology. Royal Society of Chemistry, Cambridge, Uk, 6(11):3142-3156, (2020). https://doi.org/10.1039/d0ew00361a
Impact/Purpose:
Although not regulated, ammonia has the potential to increase chlorine consumption and cause nitrification problems in the distribution system. Many groundwaters with elevated ammonia are also contaminated with other inorganic analytes such as arsenic, iron, and manganese, all of which have primary or secondary MCLs. The objective of this work was to demonstrate the effectiveness of an innovative biological treatment process to simultaneously remove ammonia (2.9 mg N/L), arsenic (23 µg/L), iron (2.9 mg/L) and manganese (80 µg/L) from a groundwater source in Iowa over a year-long pilot study. The innovative biological treatment system consisted of an “aeration contactor” followed by a conventional granular media filter. Orthophosphate was also added, as a biological nutrient, at 0.3 mg PO4/L. Ammonia, manganese, and iron were consistently reduced through the pilot system by 98 to 99%. Complete oxidation of ammonia to nitrate was observed (i.e., no nitrite was released) and arsenic was consistently removed to below the 10 µg/L MCL. The treatment mechanisms were oxidation. Ammonia was oxidized by ammonia and nitrite oxidizing bacteria and arsenic by bacteria which converted As(III) in the source water to more readily removable As(V). Iron was presumably oxidized by oxygen during aeration although some biologically assisted oxidation could not be ruled out. As(V) bound iron particles were removed in the filter resulting in effective arsenic (and iron) reduction. A surprising treatment benefit was the effective manganese reduction, the mechanism of which was not so clear, but was attributed to biologically assisted oxidation of Mn(II). While some system acclimation time was necessary to achieve desired ammonia and manganese reductions, acceptable arsenic and iron reductions were observed shortly after start-up.
Description:
Although not regulated, ammonia has the potential to increase chlorine consumption and cause nitrification problems in the distribution system. Many groundwaters with elevated ammonia are also contaminated with other inorganic analytes such as arsenic, iron, and manganese, all of which have primary or secondary MCLs. The objective of this work was to demonstrate the effectiveness of an innovative biological treatment process to simultaneously remove ammonia (2.9 mg N/L), arsenic (23 µg/L), iron (2.9 mg/L) and manganese (80 µg/L) from a groundwater source in Iowa over a year-long pilot study. The innovative biological treatment system consisted of an “aeration contactor” followed by a conventional granular media filter. Orthophosphate was also added, as a biological nutrient, at 0.3 mg PO4/L. Ammonia, manganese, and iron were consistently reduced through the pilot system by 98 to 99%. Complete oxidation of ammonia to nitrate was observed (i.e., no nitrite was released) and arsenic was consistently removed to below the 10 µg/L MCL. The treatment mechanisms were oxidation. Ammonia was oxidized by ammonia and nitrite oxidizing bacteria and arsenic by bacteria which converted As(III) in the source water to more readily removable As(V). Iron was presumably oxidized by oxygen during aeration although some biologically assisted oxidation could not be ruled out. As(V) bound iron particles were removed in the filter resulting in effective arsenic (and iron) reduction. A surprising treatment benefit was the effective manganese reduction, the mechanism of which was not so clear, but was attributed to biologically assisted oxidation of Mn(II). While some system acclimation time was necessary to achieve desired ammonia and manganese reductions, acceptable arsenic and iron reductions were observed shortly after start-up.
URLs/Downloads:
DOI: The Removal of Ammonia, Arsenic, Iron and Manganese by Biological Treatment from a Small Iowa Drinking Water System
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