Combined effect of the assimilable organic carbon and residual chlorine on the bacterium activities in drinking water

This paper aims to introduce our research findings on the combined effects of the assimilable organic carbon(AOC)and residual chlorine on the activities of bacteria in drinking water.In proceeding with our work,we have added Escherichia coli in the distribution system to the water samples and used them as an experimental target.And,then,we have added sodium hypochlorite to the water samples to make the initial concentrations of the residual chlorine equal to 0.3 mg/L and 0.6 mg/L.On the other hand,the water sample added with no sodium hypochlorite can also be used as the contrast group.The experiment was supposed to last 72 hours,during which period the flow cytometry can be used as a basic experimental method to test the changing situation of the concentrations of AOC and the living bacteria,which can be determined with a batch growth of natural microbial consortium.The concentration of the living bacteria can then be worked out by the bacteria stained with SYBR Green Ⅰ and the mixed dye of SYBR Green Ⅰ and propidium iodide.The initial concentration of AOC has been found to be 168.44 μg/L in all of the water samples.When we added the sodium hypochlorite,the concentration of AOC would be found obviously fluctuated,which tends to be caused by the oxidation of some kinds of organic carbon.The concentrations of the living bacteria can then be found decreased from 1.06 × 105cells/mL to 2.61 × 104cells/mL(0.6mg/L residual chlorine) and 4.81 × 104cells/mL(0.3 mg/L residual chlorine).The results of the experiments demonstrate that the final concentration of the living bacteria turns to be in positive correlation with the initial concentration of the residual chlorine.On the contrary,the concentration of AOC in the control group has been found behaving less fluctuated than the experimental group and the concentration of the living bacteria was increased from 1.06 × 105cells/mL to 1.81 × 105cells/mL in 72 hours.The results of our experiments suggest that when we use the moderate chlorine disinfectant to dispose of the drinking water with microorganism,the activity of the bacteria has been mainly inhibited by the residual chlorine,though the re-growth capacity of bacetria endowed with by the AOC proves to be relatively weak and meager.