Title:
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Laboratory investigation on bromoform formation in potable water of Kuwait
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Bromoform compound is occasionally found in concentrations above 100 µg/l (WHO guideline limit for bromoform is 100 µg/l) in the potable water of Hawali city, Kuwait. The compound has been classified as a 'possible human carcinogen'. In this research study, a laboratory investigation was carried out to assess bromoform precursors in the sources (i.e. groundwater and recarbonated water) of potable water at the Doha blending facility, Kuwait; to perform correlation analysis between bromoform and the following parameters: Δ chlorine, ultra violet (UV₂₅₄) absorbance, and the pH of the water samples; to determine the significant effects of the preparation method (i.e. blending of the sources water during production of potable water), storage period, temperature, and their interactions on the development of bromoform; to determine under which of the tested laboratory conditions the development of bromoform in the simulated residence time tests was the lowest; to formulate bromoform predictive models, and the development of a bromoform management strategy to overcome such problem. The methodology that was used to answer the research objectives included chemical analysis for the source water samples collected from Doha blending facility, a series of laboratory tests to a simulated residence time, a statistical technique to develop a mixed effects model, a correlation analysis, and a multiple regression analysis. The results indicated that the groundwater consisted of bromide (0.71 mg/l), thus, increasing the groundwater percentage during production of potable water would result in the development of more bromoform. The other source of potable water (recarbonated water) consisted of a considerable amount of bromoform (30 µg/l). This amount may reach the WHO guideline limit either during the potable water production cycle or during the delivery of water to the consumers. The results of the correlation analysis showed that there was a strong positive correlation between bromoform and Δ chlorine, a positive moderate correlation between bromoform and UV254 absorbance, and a negative weak relationship between bromoform and the pH of water samples. The results of the mixed effects model analysis indicated that the preparation method, temperature, and storage period (represented the main effects in the model) have a highly significant effect (p < 0.001) on the development of bromoform in water samples. Furthermore, the interaction effects of the temperature and preparation method, and also the preparation method and storage period, showed a highly significant effect (p < 0.001). Meanwhile, no significant interaction effect was observed between temperature and storage period on the development of bromoform. The lowest average bromoform concentration (29.28 µg/l) was measured in the simulated residence time test conducted on synthetic potable water samples comprising 2.9% groundwater under 20º C temperature conditions which represents the optimum operation conditions to be considered at the Doha blending facility in the production of potable water. Bromoform predictive model was formulated using water quality data obtained from the simulated residence time tests conducted on synthetic potable water samples. The performance of the model was evaluated by calculating mean absolute errors using separate data sets. Assessment of the bromoform model indicated that the model has a good prediction ability. Finally, a bromoform management strategy was proposed to control the presence of bromoform covering all stages of the potable water production cycle which include introducing guidelines toward water quality and operational conditions, using alternative disinfection methods for the treatment of seawater and the finished potable water, management of the groundwater utilised in the production of potable water, and organising a maintenance plan for the related water distribution system.
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