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3.1.2 Removal of Natural Organic Matter (NOM) <br />Song (1999) documented the impact of NOM on chloramine decay by altering NOM <br />concentrations through GAC adsorption of the test water. Figure 2 shows the impact of NOM on <br />chloramine decay rates. <br />2.4 ,--- - <br />2.0 <br />R.11a=D01- <br />A <br />0.02 - = Ce. ': u; ?- <br />O <br />L ' <br />[J <br />O g oTOC = 0.3 mg,L, 22 my:L C121n.lial sp:ka <br />c <br />r- gTOG = 1.0 mgiL, 2,3 mg.2 Cl2 initial spike <br />n 4 TOG = 2.0 mgit. 2.4 mg,L Cl2 Initial spike <br />■ T 0C = 2.0 mgjL, 25 mgl Cl2 initial sp ke <br />a.L1 <br />10 is 2C 215 <br />Time (days) <br />Figure 2 <br />Elimination of Chloramine -NOM Reaction by TOC Removal with GAC Adsorption in USL WTP <br />Filtered Water at pH = 8.5 <br />Source: Song 1999. <br />For the lowest TOC condition, only the autodecomposition pathway occurred. Bone et al (1999) <br />hypothesized that the NOM oxidation mechanism is the dominant pathway for chloramine decay <br />early in the decay process (i.e., within 24 hours), and that autodecomposition is the dominant <br />cause of chloramine decay later. <br />3.1.3 pH and Alkalinity <br />Bulk water pH value is an important factor in nitrification activity for two reasons. First, a <br />reduction of total alkalinity may accompany nitrification because a significant amount of <br />bicarbonate is consumed in the conversion of ammonia to nitrite. A model developed by Gujer <br />and Jenkins (1974) indicates that 8.64 mg/L of bicarbonate (HCO3-) will be utilized for each <br />mg/L of ammonia -nitrogen oxidized. While reduction in alkalinity does not impose a direct <br />public health impact, reductions in alkalinity can cause reductions in buffering capacity, which <br />can impact pH stability and corrosivity of the water toward lead and copper. The relationships <br />between pH, alkalinity, corrosivity, and metals leaching are addressed in a separate White Paper. <br />Secondly, nitrifying bacteria are very sensitive to pH as shown in Figure 3. Nitrosomonas has an <br />optimal pH between approximately 7.0 and 8.0, and the optimum pH range for Nitrobacter is <br />approximately 7.5 to 8.0. Some utilities have reported that an increase in pH (to greater than 9) <br />Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 9 <br />