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Chloramination has replaced free chlorine as a secondarydisinfectant at many utilities because of regulationslimiting trihalomethanes (THMs) and haloaceticacids (HAAs) in the distribution system. Chloramineuse is advantageous because it forms substantiallylower concentrations of THMs and HAAs than freechlorine. However, the potential for nitrification,which is the bacterially mediated conversion of ammoniato nitrite and nitrate, is a trade-off that utilitiesmust consider in their monitoring and maintenancepractices.Although many theoretical aspects of nitrification areunderstood, practical management of the chloraminateddistribution system still poses a challenge to utility managers.The absence of adequate data collection to assessnitrifying conditions and the absence of a comprehensiveframework for analyzing this data contribute to thedifficulties in effectively managing a chloraminated distributionsystem to eliminate or minimize nitrification.In this article, nitrification potential curves are introducedas a possible operational strategy to prevent nitrificationin chloraminated distribution systems. Nitrificationpotential curves are constructed based on the parametersthat define growth and inactivation kinetics ofammonia-oxidizing bacteria (AOB) in environmentsthat contain chloramine and ammonia. To demonstratethe applicability of nitrification potential curves, theauthors conducted long-term, pilot-scale studies thatcovered a range of chlorine-to-ammonia applicationratios and chloramine residual concentrations that aretypical of full-scale chloraminated systems.Results indicate that the total chlorine and freeammonia concentrations associated with the presenceor absence of nitrification are closely linked to thegrowth and inactivation kinetics of AOB in the distributionsystem. These growth and inactivation kineticscan be estimated to produce a nitrification potentialcurve that predicts whether the system's operatingconditions are likely to lead to nitrification. Thestraightforward methodology outlined may be usefulfor full-scale system assessment to explain the presenceand absence of nitrification. Includes 33 references, tables, figures.

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Edition: Vol. 97 - No. 8 Published: 08/01/2005 Number of Pages: 10 File Size: 1 file , 310 KB