SR0082168 - Laserfiche WebLink

Home Browse Search

3.0 Prevention/Mitigation Methods Both groups of nitrifying bacteria are obligate aerobic organisms commonly found in terrestrial and aquatic environments (Holt et al. 1995, Watson et al. 1981). Their growth rates are controlled by: ■ Substrate (ammonia -N) concentration, ■ Temperature, ■ pH, ■ Light, ■ Oxygen concentration, and ■ Microbial community composition. Water quality and environmental factors affecting nitrification are discussed below. 3.1 Source Water Treatment 3.1.1 Sources of Ammonia, Nitrate, and Nitrite Excess nitrogen in the form of ammonia in finished water can be the principal cause of nitrification since ammonia serves as the primary substrate in the nitrification process. Ammonia, nitrate and nitrite can typically be found in surface water supplies as a result of natural processes. These natural sources of nitrogen generally have minimal impacts on water supply distribution systems because the concentration of nitrite nitrogen in surface and ground waters is normally far below 0.1 mg/L (Sawyer and McCarty, 1978). Other sources of nitrogen can include agricultural runoff from fertilization or livestock wastes or contamination from sewage. Ammonia also occurs naturally in some groundwater supplies, and groundwater can become contaminated with nitrogen as agriculture runoff percolates into aquifers. A survey of 67 large utilities (greater than 50,000 customers) found that average levels of raw water nitrate ranged from 0 to 5.7 mg/L (Kirmeyer et al. 1995). To protect public health, any system with source water that exceeds the inorganic contaminant MCLs for nitrate and nitrite of 10 mg/L and 1 mg/L (as Nitrogen), respectively, must treat the water to below those levels (USEPA 2001). However, if a water treatment plant removes nitrate and nitrite levels to just meet the MCLs, and the water system uses chloramine for disinfection, there is a potential for nitrate and nitrate values during a nitrification event to exceed the numeric values of their respective MCLs. Ammonia is deliberately added to a chloraminated water supply. In these systems, the concentration of free ammonia present in the distributed water will be a function of the chlorine to ammonia -N (C12:NH3-N) ratio. Free ammonia is almost completely eliminated when a 5:1 weight ratio of C12:NH3-N is used (Kirmeyer et al. 1993). Nitrate/nitrite-N formation results presented previously in Table 3 showed that the lowest amount of nitrate/nitrite-N is formed when a 5:1 ratio is used. Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 8