Abstract
Nitrification is a major issue that utilities must address if they utilize chloramines as a secondary disinfectant. Nitrification is the oxidation of free ammonia to nitrite which is then further oxidized to nitrate. Free ammonia is found in drinking water systems as a result of overfeeding at the water treatment plant (WTP) or as a result of the decomposition of monochloramine. Premise plumbing systems (i.e., the plumbing systems within buildings and homes) are characterized by irregular usage patterns, high water age, high temperature, and high surface-to-volume ratios. These characteristics create ideal conditions for increased chloramine decay, bacterial growth, and nitrification. This review discusses factors within premise plumbing that are likely to influence nitrification, and vice versa. Factors influencing, or influenced by, nitrification include the rate at which chloramine residual decays, microbial regrowth, corrosion of pipe materials, and water conservation practices. From a regulatory standpoint, the greatest impact of nitrification within premise plumbing is likely to be a result of increased lead levels during Lead and Copper Rule (LCR) sampling. Other drinking water regulations related to nitrifying parameters are monitored in a manner to reduce premise plumbing impacts. One way to potentially control nitrification in premise plumbing systems is through the development of building management plans.
Highlights
Water utilities across North America, Europe, and Australia have adopted the use of chloramine as a secondary disinfectant, an alternative to free chlorine, to avoid the formation of disinfectant by-products (DBPs) and to maintain a greater residual stability in their drinking water distribution systems (DWDSs) [1,2,3,4]
While chloramine is known to be more stable than free chlorine under normal operating conditions, the onset of nitrification can greatly increase the rate of chloramine decay resulting in a less stable residual
Nitrification is a two-step process where ammonia-oxidizing bacteria (AOB) oxidize free ammonia, either resulting from dosing at the water treatment plant (WTP) or released from chloramine decay, to nitrite followed by Nitrite Oxidizing Bacteria (NOB) that oxidize nitrite to nitrate
Summary
Water utilities across North America, Europe, and Australia have adopted the use of chloramine as a secondary disinfectant, an alternative to free chlorine, to avoid the formation of disinfectant by-products (DBPs) and to maintain a greater residual stability in their drinking water distribution systems (DWDSs) [1,2,3,4]. Monochloramine has been shown to reduce the colonization of Legionella spp. in premise plumbing systems [7,8]. The 2017 survey, along with a 1996 phone survey, indicated that, of the utilities that are using chloramine as a secondary disinfectant, roughly two-thirds experience nitrification to at least some degree in their DWDS [11,12]. The goal of this review is to summarize both the nitrification process in drinking water distribution systems in general and within premise plumbing systems. While other reviews exist on nitrification, this review aims to synthesize information regarding different aspects of premise plumbing systems that could impact nitrification and influence drinking water quality at the point of use. Some references within were found using textbooks and reference manuals relevant to the field
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