Temperature dependence of chemical and microbiological chloramine decay in bulk waters of distribution system

Abstract

Chloramine decays in distribution system due to wall and bulk water reactions. In bulk water, the decay could either be due to chemical or microbiological reactions. Without such distinction it is not possible to model chloramine decay in an actual distribution system since microbiological decay depends on different factors compared with chemical decay. The dependence of chloramine decay on chemical reactions is mostly understood. Although it is widely accepted that microbiological reactions could accelerate chloramine decay, quantification had not been possible until the microbiological decay factor method was proposed. In this paper, the effect of temperature on microbial and chemical decay coefficients is presented. This was done by following the procedure of the microbiological decay factor method but by varying the temperature of incubation between 18 and 30°C. The procedure was repeated for several samples. The results indicated that it is possible to express temperature dependence of both microbiological and chemical coefficients using the Arrhenius equation within the tested temperature range. Estimated E/R values were found to be 3,551±705 K−1 and 6,924±1,700 K−1 for chemical and microbiological decay rates respectively. Traditionally, it is believed that every 10°C rise would double the decay rate coefficients. However, the E/R value estimated in this study shows that a 16–17°C temperature rise is needed to double the chemical chloramine decay rate. A possible application to predict residuals in summer using winter water quality results is demonstrated. Results indicated that microbial decay factor method could help pre-warning water utilities of possible residual loss in summer. Traditional indicators could not offer such distinction.

Batch test to evaluate microbial disinfectant decay and the onset of nitrification

“…The distribution systems studied here have maximum annual temperatures in the same range at which the test was conducted (20-22°C), and the warmest months are when there is the greatest need to be vigilant about nitrification events and other reactions accelerating the decay of the disinfectant residual. In cooler months, or in distribution systems where the peak temperatures differ from the temperature at which the batch test is conducted, a correction could be made to account for the impact of temperature, for example, using the approach described by Sathasivan et al (2009). The results in Table 2 support the observations of Sathasivan et al (2008) that monochloramine decay often occurs in two phases, with a greater decay rate in the second phase (k T2 higher than k T1 ).…”

“…Those authors used the batch test method developed in Sathasivan et al (2005) to determine a target dilution that would yield an acceptable F m (and overall decay rate), since diluting the stagnated reservoir water with freshly treated water was their strategy for improving water quality. In addition, temperature can also influence the time required to reach CTR, since lower water temperature will reduce microbial growth rates and can affect the biostability and onset of nitrification in disinfected waters (Sathasivan et al 2009;Sarker et al 2013). However, batch test results can provide an early warning that conditions at a site can be susceptible to rapid chloramine decay caused by nitrification at warmer temperatures.…”

Environmental Management of Legionella in Domestic Water Systems: Consolidated and Innovative Approaches for Disinfection Methods and Risk Assessment

“…However, in large buildings with complex plumbing systems, it can be difficult to reach these temperatures. On the other hand, elevated water temperatures accelerate disinfectant decay (e.g., chloramines and chlorine) [ 6 , 7 ] and predispose hot water systems to deteriorating microbial water quality [ 8 ]. Finally, when it is possible to achieve and maintain high water temperatures, the risk of scalding increases significantly.…”

Thermal energy recovery from chlorinated drinking water distribution systems: Effect on chlorine and microbial water and biofilm characteristics

“…As a key influencing factor in DWDS, temperature can affect both chemical and biological processes (Li et al, 2019). Chlor(am)ine decay rate can be accelerated with increasing temperature (Monteiro et al, 2017;Sathasivan et al, 2009). This can be explained by two major reasons: (i) chlor(am)ine self-decay is a temperature dependent reaction, and the reaction rate is higher at higher temperature (Monteiro et al, 2017); (ii) elevated temperature can change the microbial activities (Ndiongue et al, 2005).…”