Prechlorination Disinfection and Its Effect on Coagulation in Water Treatment
Disinfection efficiency is epresented by the inactivation rate of pathogenic microorganisms after the application of disinfectants. To ensure the drinking water safety, many countries have included this item in the assessment of drinking water treatment efficiency. On November, 1997, ERA in Taiwan, ROC, promulgated a policy that requires water facilities provide disinfection efficiency report when their source water does not comply with the standard for drinking water. Therefore, it is important to evaluate the existiong chlorination processes and other treatment facilities in order to achieve better disinfection efficiency and meet the increasingly strict safety drinking water standard. Most research about disinfection are focused on post-chlorination, because it is more commonly practiced in many countries. However, both pre- and pos-chlorination are practiced in Taiwan, due to the high contents of ammonia-nitrogen and algae in source water. Furthermore, since water quality can significantly affect the disinfection efficiency, the results from ther countriex may not apply to all situations. In this study, the variations on disinfection efficiency with the contact time and residual chlorine at various chlorine dosage were evaluated. The efficiencies of disinfection and coagulation by means of pre- and post-chlorination were also studied. Water samples were collected from various points in the water treatment plant , namely, after rapid mixing, sedimentation, filtration and finished tank to analyze microbial removal and other water quality treatment efficiency. The results showed that the current pre-chlorination could meet the disinfection standard required by the law. However, the application of chlorine in the process might be overdosed. The coexistence of the coagulate with the disinfectant did not decrease the disinfection efficiency, unless the coagulant was added before the complete mixing of the disinfectant.
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