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Biological Treatment Simultaneously Address Multiple Contaminants: Ammonia, Arsenic, Iron and Manganese (Canada)
Citation:
Lytle, D., D. WILLIAMS, C. MUHLEN, M. N. PHAM, AND E. RIDDICK. Biological Treatment Simultaneously Address Multiple Contaminants: Ammonia, Arsenic, Iron and Manganese (Canada). 2018 American Water Works Association WQTC, TorontoCON, November 11 - 15, 2018.
Impact/Purpose:
Intensive agricultural practices in North America contribute significant amounts of ammonia to surface and ground water supplies. While not regulated as a contaminant in finished drinking water, ammonia has the potential to increase chlorine consumption and cause nitrification problems in the distribution system and interfere with arsenic reduction. Coincidentally, in many parts of the Midwest, groundwaters with elevated ammonia are also contaminated with arsenic, iron, and manganese all of which have primary or secondary MCLs. The investigators have successfully demonstrated an innovative, technically simple and operationally inexpensive aerobic biological process to reduce several of these contaminants individually. The objective of this presentation is to present the results of a pilot study using this innovative biological treatment system to simultaneously remove ammonia, arsenic, iron and manganese. Specifically, a 6-month long pilot study was performed in Iowa on a ground water that had 23 µg/L arsenic, 80 µg/L manganese, 2.9 mg/L iron and 2.9 mg N/L ammonia. The innovative biological treatment system consists of an “aeration contactor” followed by a conventional granular media filter. Orthophosphate was added as a biological nutrient at 0.3 mg PO4/L. A great benefit to the system is that it is operated without the addition of any other chemicals including strong oxidants such as permanganate commonly used to oxidize arsenic and remove manganese. The system was operated under various loading rates and engineering parameters to optimize removal all four contaminants and that process will be discussed. Results showed that ammonia, manganese, and iron were reduced through the pilot system by consistently more than 98-99%. Complete oxidation of ammonia was observed (no nitrite released). Arsenic was consistently removed to below the 10 µg/L MCL. Ammonia oxidation by ammonia and nitrite oxidizing bacteria, and arsenic oxidization by bacteria converting As(III) in the source water to more readily removable As(V) (data will be presented) were treatment mechanisms. 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. The 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 achieved desired ammonia and manganese reductions, acceptable arsenic and iron reductions were observed shortly after start-up. Other water quality parameters and HPC levels through the system will be presented, and the impact of contactor and filter loading rates, pH, oxygen concentration and chlorinated backwash on performance will all be discussed. Lastly, the innovative biological process described in this work evolved from an idea than led to laboratory pilot studies, field pilot testing and full-scale design. The steps taken to develop and commercialize the EPA technology through partnerships with local and state government, and private industry will be briefly discussed.
Description:
Intensive agricultural practices in North America contribute significant amounts of ammonia to surface and ground water supplies. While not regulated as a contaminant in finished drinking water, ammonia has the potential to increase chlorine consumption and cause nitrification problems in the distribution system and interfere with arsenic reduction. Coincidentally, in many parts of the Midwest, groundwaters with elevated ammonia are also contaminated with arsenic, iron, and manganese all of which have primary or secondary MCLs. The investigators have successfully demonstrated an innovative, technically simple and operationally inexpensive aerobic biological process to reduce several of these contaminants individually. The objective of this presentation is to present the results of a pilot study using this innovative biological treatment system to simultaneously remove ammonia, arsenic, iron and manganese. Specifically, a 6-month long pilot study was performed in Iowa on a ground water that had 23 µg/L arsenic, 80 µg/L manganese, 2.9 mg/L iron and 2.9 mg N/L ammonia. The innovative biological treatment system consists of an “aeration contactor” followed by a conventional granular media filter. Orthophosphate was added as a biological nutrient at 0.3 mg PO4/L. A great benefit to the system is that it is operated without the addition of any other chemicals including strong oxidants such as permanganate commonly used to oxidize arsenic and remove manganese. The system was operated under various loading rates and engineering parameters to optimize removal all four contaminants and that process will be discussed. Results showed that ammonia, manganese, and iron were reduced through the pilot system by consistently more than 98-99%. Complete oxidation of ammonia was observed (no nitrite released). Arsenic was consistently removed to below the 10 µg/L MCL. Ammonia oxidation by ammonia and nitrite oxidizing bacteria, and arsenic oxidization by bacteria converting As(III) in the source water to more readily removable As(V) (data will be presented) were treatment mechanisms. 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. The 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 achieved desired ammonia and manganese reductions, acceptable arsenic and iron reductions were observed shortly after start-up. Other water quality parameters and HPC levels through the system will be presented, and the impact of contactor and filter loading rates, pH, oxygen concentration and chlorinated backwash on performance will all be discussed. Lastly, the innovative biological process described in this work evolved from an idea than led to laboratory pilot studies, field pilot testing and full-scale design. The steps taken to develop and commercialize the EPA technology through partnerships with local and state government, and private industry will be briefly discussed.