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Elevated Natural Source Water Ammonia and Nitrification in the Distribution Systems of Four Water Utilities
Citation:
LYTLE, D. A., C. MUHLEN, AND B. ALMASSALKHI. Elevated Natural Source Water Ammonia and Nitrification in the Distribution Systems of Four Water Utilities. Presented at 2007 AWWA WQTC Conference, Charlotte, NC, November 04 - 08, 2007.
Impact/Purpose:
To inform the public.
Description:
Nitrification in drinking water distribution systems is a concern of many drinking water systems. Although chloramination as a source of nitrification (i.e., addition of excess ammonia or breakdown of chloramines) has drawn the most attention, many source waters contain significant levels of ammonia. Accompanying nitrification is the potential for the formation of nitrite and nitrate in the distribution system, both of which have MCLs of 1 mg/L NO2-N and 10 mg/L NO3-N , respectively. These contaminants are regulated at the point of entry into the distribution system, and are not regulated nor monitored at the consumer’s tap. Four small drinking water systems in Illinois have reported free ammonia concentration between 2.9 to 10.1 mg/L NH3-N entering their distribution systems (nitrite and nitrate are typically very low). Taste and odor complaints are often reported, and nitrification in their distribution systems is thought to be an issue although not documented. The objective of this work was to monitor and report ammonia, nitrite, and nitrate (and other water quality parameters) levels in drinking waters from the distribution systems of four drinking water utilities in Illinois that have elevated free ammonia entering their distribution systems. A discussion of approaches used by the sites to reduce free ammonia levels entering their systems and reducing nitrification once it occurs will be provided. The drinking water utilities provided four to six sampling locations in their distribution systems. The sites were spread-out fairly evenly over the distance of their distribution system (close, mid-way, and far from treatment plant). Samples were analyzed for metals, alkalinity, ammonia, nitrite, nitrate as well as on site pH, temperature, and total chlorine. The four test sites had raw water ammonia concentrations greater than 4.3 mg N/L. Free ammonia levels ranged between 2.9 to 10.1 mg/L NH3-N entering their distribution systems. Distribution system nitrite levels ranged between non-detectable to 3.5 mg/L NO2-N, and many values were greater than 1 mg/L NO2-N. Nitrite levels generally increased with distance away from plant and highest nitrite levels were typically seen in locations farthest in distance from the treatment plant. Nitrate levels were observed between 0 to 2.8 mg/L NO3-N, and the highest values were noted at sites in the mid to far distance range of the distribution systems. Locations with greatest nitrite levels tended to have little to no total chlorine present. Community awareness of the nitrification problems prompted the sites to take action which included optimizing ion exchange softening regeneration frequency for ammonia removal, increasing chlorine addition and improving distribution system maintenance (e.g., flushing) programs. Also, biological nitrification filtration as a “pre-filter” for ammonia oxidation to nitrate was considered and will be discussed.