Nitrification is a major challenge in chloraminated drinking water systems, resulting in undesirable loss of disinfectant residual. Consequently, heterotrophic bacteria growth is increased, which adversely affects the water quality, causing taste, odour, and health issues. Regular monitoring of various water quality parameters at susceptible areas of the water distribution system (WDS) helps to detect nitrification at an earlier stage and allows sufficient time to take corrective actions to control it. Strategies to monitor nitrification in a WDS require conducting various microbiological tests or assessing surrogate parameters that are affected by microbiological activities. Additionally, microbial decay factor (Fm) is used by water utilities to monitor the status of nitrification. In contrast, approaches to manage nitrification in a WDS include controlling various factors that affect monochloramine decay rate and ammonium substrate availability, and that can inhibit nitrification. However, some of these control strategies may increase the regulated disinfection-by-products level, which may be a potential health concern. In this paper, various strategies to monitor and control nitrification in a WDS are critically examined. The key findings are: (i) the applicability of some methods require further validation using real WDS, as the original studies were conducted on laboratory or pilot systems; (ii) there is no linkage/formula found to relate the surrogate parameters to the concentration of nitrifying bacteria, which possibly improve nitrification monitoring performance; (iii) improved methods/monitoring tools are required to detect nitrification at an earlier stage; (iv) further studies are required to understand the effect of soluble microbial products on the change of surrogate parameters. Based on the current review, we recommend that the successful outcome using many of these methods is often site-specific, hence, water utilities should decide based on their regular experiences when considering economic and sustainability aspects.

Inorganic chloramines are not commercially available, but monochloramine is produced in situ for disinfection or for use in chemical synthesis. Inorganic chloramines are also formed when free chlorine reacts with nitrogen containing substances, e.g. ammonia and urea, present in chlorinated water sources. Occupational exposure may, therefore, occur in e.g. swimming pool facilities and the food processing industry. Monochloramine is soluble and stable in water and the dominating inorganic chloramine in chlorinated water sources. No clinical effects were seen in healthy volunteers given monochloramine in drinking water during 4 or 12 weeks in doses of 0.043 or 0.034 mg/kg bw/day, respectively. Limited data indicate that monochloramine is weakly mutagenic in vitro but not genotoxic in vivo. One drinking water study indicated equivocal evidence of carcinogenicity in female rats but not in male rats and mice. No reproductive or developmental effects were shown in rodents in the few studies located. Dichloramine is soluble but unstable in water. In the only study located, mild histological effects in kidneys, thyroid and gastric cardia were observed in rats administered dichloramine in drinking water for 13 weeks. Trichloramine is immiscible with water and evaporates easily from water into air. Therefore, the primary exposure route of concern in the occupational setting is inhalation. Occupational exposure to trichloramine has been demonstrated in indoor swimming pool facilities and in the food processing industry where chlorinated water is used for disinfection. Exposure-response relationships between airborne levels and self-reported ocular and upper airway irritation have been shown in several studies. Exposure to trichloramine may aggravate asthma symptoms in individuals with existing asthma. The risk of developing asthma following long-term exposure to trichloramine cannot be evaluated at present. No data on genotoxic, carcinogenic, reproductive or developmental effects were located. The toxicological data for mono- and dichloramine are insufficient to recommend health-based occupational exposure limits (OELs).As regard trichloramine, the critical effect is judged to be irritation observed in several studies on pool workers, starting at approximately 0.4 mg/m3 (stationary sampling). Based on these data, a health-based OEL of 0.1 mg/m3 (8-h time-weighted average) is recommended. This corresponds to 0.2 mg/m3 for stationary measurements in swimming pool facilities. No short-term exposure limit (STEL) is recommended.