Investigation of Chloramines, Disinfection Byproducts, and Nitrification in Chloraminated Drinking Water Distribution Systems.

Four chloraminated drinking water distribution systems (CDWDSs) required to maintain numeric versus "detectable" residuals were spatially and temporally sampled for water quality and associated trihalomethane (THM) and haloacetic acid (HAA) formation. Monochloramine decreased from entry point (EP) to maximum residence time (MRT) samples while THMs and HAAs initially increased and then stabilized or slightly decreased. Subsequently, EP and MRT samples were used in laboratory-held studies to further evaluate disinfectant residual stability, chloramine speciation, and nitrification occurrence. MRT water exhibited a faster monochloramine concentration decline compared to EP water, indicating a decreasing disinfectant residual stability from increasing water age through distribution. Using a simple technique based on published inorganic chloramine chemistry, samples were also investigated for nondisinfectant positive interference (NDPI) on total chlorine measurements. NDPI concentrations represented up to 100% of the total chlorine concentration when total chlorine concentrations decreased to 0.05 mg-Cl2/L, indicating little to no effective disinfectant residual remained.

Temperature impact on monochloramine, free ammonia, and free chlorine indophenol methods.

A commercial colorimetric indophenol (IP) method is used for determining monochloramine (NH2Cl) concentrations for process control in chloraminated public water systems and chloramine-related research. The NH2Cl - IP method excludes some quality control procedures typically included in drinking water methods and is not approved by the United States Environmental Protection Agency (U.S. EPA) for compliance monitoring. Therefore, the authors developed and validated a more complete NH2Cl-IP method, building on the commercial technique, as a candidate for future approval. During method development, temperature impact on color development was investigated. Color development time increased as temperature decreased. Below 20 °C, times needed for full color development were greater than those reported in the commercial method, reaching nearly three times longer at 5 °C. This observed temperature dependence also applies to free ammonia and free chlorine indophenol methods. To avoid measurement errors of samples analyzed below 20 °C, use of reaction times determined in this study is recommended for these indophenol methods.

Chlorinated Cyanurates in Drinking Water: Measurement Bias, Stability, and Disinfectant Byproduct Formation.

Two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) and trichlor (trichloroisocyanuric acid) may be approved for use in United States drinking water systems as chlorine sources. One complication with dichlor or trichlor's application in drinking water is that the actual free chlorine concentration in these systems cannot be quantified accurately by currently approved methods. Based on known water chemistry, two hypothesized advantages of dichlor or trichlor use are potential increased residual chlorine stability and decreased regulated disinfectant byproduct (DBP) formation. To inform these practical considerations, the current research investigated measurement bias in N,N-diethyl-p-phenylenediamine (colorimetric and portable parallel analyzer), indophenol, amperometric titration, and amperometric electrode free chlorine methods. In addition, hold studies using a surface water and dosed with either free chlorine only, dichlor, or trichlor provided the first side-by-side comparisons of disinfectant residual stability and regulated DBP formation.

A Drinking Water Relevant Water Chemistry Model for the Free Chlorine and Cyanuric Acid System from 5 to 35 °C.

In the United States, approved methods to measure free chlorine concentrations in drinking water systems adding sodium dichloroisocyanurate (dichlor) or trichloroisocyanuric acid (trichlor) as chlorine sources exhibit measurement bias from chlorinated cyanurate presence, leading to overestimated free chlorine concentrations for regulatory compliance. One option to overcome this limitation is to estimate free chlorine concentrations using an established water chemistry model (full model), but the full model has only been determined for 25 °C. The current research used a simplified version of the full model (simple model) and estimated the unknown temperature dependence (5 to 35 °C) of the two remaining equilibrium constants (K7a and K9a) required for the simple model. At 0 M ionic strength (µ), lnK7a=−4,671TK+4.95 or pK7a=2,028TK−2.15, ΔH7a0=38.8±6.0 kJ mol−1 (95% confidence interval, CI), lnK9a=−5,133TK+3.79 or pK9a=2,229TK−1.65, and ΔH9a0=42.7±3.0 kJ mol−1 (95% CI). At 25 °C and µ of 0 M, the simple model estimated pK7a and pK9a are 4.65 ± 0.059 (95% CI) and 5.83 ± 0.020 (95% CI), respectively. As an example of temperature's impact, the free chlorine concentration for a 2 mg Cl2 L−1 dichlor addition (pH 7.0) decreases from 0.90 mg Cl2 L−1 free chlorine at 25 °C to 0.60 mg Cl2 L−1 free chlorine at 5 °C. If temperature was not considered, a system operating at 5 °C would overestimate their free chlorine concentration by 50%, which could have significant implications for understanding disinfection efficacy, illustrating the developed model's significance.