Studies On Combined Disinfection Processes Of Chlorine And Chloramines In Drinking Water

The object of this thesis research is to improve the short-term free chlorine plus chloramines disinfection process, based on this study multi-point sequential chlorination process is established and studied. A combined disinfection process, which is effective to control both microorganisms and disinfection by-product(DBPs), is explored by changing the chlorine and chloramines disinfectant dosing points, the dosage dose, time and other factors.It has been found that short-term chlorine disinfection and chloramines disinfection had synergetic effect on microorganism inactivation. This study focused on the difference of synergetic effect with different kinds of microorganism. The inactivation efficiency of sequential chlorination process on E.coli, S. aureus and P. aeruginosa was better than that of free chlorination or monochloramination of same available chlorine dosage individually, which means the existence of synergetic effect on these bacteria. However, this synergetic effect did not exist with the sequential chlorination on the spore of Bacillus subtilis. The investigation of DBPs at the effluent of water plant and the long residence time within the distribution system showed that sequential chlorination process generated far less halo-DBPs than free chlorine disinfection.The study of multi-point sequential chlorination process was based on sequential chlorination process and disinfectant dosage experiences of water plants. Experiments carried with both laboratory water and actual water showed that changing disinfectants dosing points and dosage dose could effectively reduce DBPs formation. At the same time, the advantages of sequential chlorination process on microorganisms and DBPs still worked well. These two aspects ensured the multi-point sequential chlorination process be a more safe disinfection.Two-points-short-term free chlorine plus chloramines disinfection process was used in conventional treatments of water supply as one of the multi-point sequential chlorination process. The process is adding chlorine at the start of filtration and clear well respectively and immediately adding ammonia to change the chlorine to chloramines in clear well. The point of chlorine dosing move up to the filtration process can decrease disinfection by-product yield and control bio-film growth in filtration process. HPC result also showed advantage in microorganism controlling.Fluorescence staining and flow cytometry (FCM) was first used in drinking water disinfection in this study. The cell concentration of microorganisms could be detected easily and accurately by fluorescence staining and FCM. Microorganism inactivation mechanism of chlorine and chloramines was found obviously different in apoptosis testing by FCM. Chlorine completely and rapidly destructed the cell membrane of bacteria, while chloramines'destruction was a slow and gradual process. Different periods of bacteria's survivals, e.g. live, dead, early apoptosis and late apoptosis, could be detected.