Over the last decade, chloramines have preferentially been used in place of chlorine as disinfectant, as a result of increasing health concerns and USEPA regulations associated with disinfection by-products (DBPs). While the switch to chloramines generally has been beneficial, subsequent to this change, several utilities have reported problems with substantially higher rates of elastomeric compound failures in their water systems.
To predict the long-term performance of elastomers within the water systems, accelerated degradation experiments were conducted at the combinations of three temperatures (23°C, 45°C and 70°C) and three chloramine concentrations (1-, 30-, and 60 mg/L concentrations) for natural rubber, neoprene rubber, ethylene propylene diene monomer (peroxide-cured), ethylene propylene diene monomer (sulfur-cured), styrene butadiene rubber and nitrile rubber. Elastomer degradation was characterized by mass change, volume change, breaking stress, breaking strain and hardness. Using a time-temperature superposition (TTS) principle the accelerated test results were 'doubly-shifted' (temperature and chloramine concentration) to service conditions to generate long-term performance curves.
As TTS technique was not suitable for mass change data, aqueous chloramine diffusion into styrene butadiene rubber and natural rubber was analyzed using Fick's second law of diffusion to develop long-term mass intake prediction curves. Diffusion coefficients were calculated for 1 mg/L chloramine concentration at three temperatures (23, 45 and 70°C) and also for 23°C, at three chloramine concentrations (1, 30 and 60 mg/L). For 1 mg/L chloramine concentration, activation energy for diffusion of SBR and natural rubber were computed to be 51.13 kJ/mole and 77.29 kJ/mole, respectively. Also, concentration profiles were developed to understand the extent of penetration along the elastomer thickness over time and temperature.
To investigate the water quality concerns as a result of accelerated elastomeric compounds degradation, accelerated degradation tests were conducted in aqueous chloramine solutions and then the solutions were analyzed for organic compounds using SPME-GC/MS. The water quality concerns that could arise because of these elastomeric compounds degradation were discussed with relevant literature review in this study.
Considering the reports of elastomeric compounds failure in chloramines disinfectant water distribution systems, this study would provide better tools for water industry in managing the risks associated with elastomer failure.
|School:||University of Louisville|
|School Location:||United States -- Kentucky|
|Source:||DAI-B 70/07, Dissertation Abstracts International|
|Subjects:||Chemical engineering, Civil engineering, Environmental engineering|
|Keywords:||Diffusion, Drinking water, Elastomers, Life-prediction, Organic compounds, SPME-GC/MS, Water distribution systems, Water quality|
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