Study On Biofilm Growth Conditions And Its Impact On Water Quality

The increase of water eutrophication and discharge of a large amount of sewage lead to a significant increase of organic pollutants in water. These new organic pollutants in water can not be removed effectively in current process, so a large quantity of organic material come into the network, and the micro-organisms inside the network over-breeding, resulting in an increased risk of microbialogical. Adcording to experiments, it reaches to the maximum amount of 2.4×106CFU/cm2 at the content of AOC of 20μg/L in 20 days at the absence of the disinfectant. Biofilm achieves stability within 60 days, the stability of biomass at 5×105CFU/cm2, a great decrease and at the same time HPC in the water up to 2×105CFU/ml. Without sterilization it needs 10 days to reach a stable state, at AOC in the level of 70μg/L and the biomass reach to 1×106CFU/cm2, the largest biomass of biofilm is only 3×106CFU/cm2. The velocity between 0.5m/s and 1.5m/s in pipe has no significant impact on biofilm biomass. Cast iron pipe is the most suitable for biofilm growth compared with galvanized pipe and PVC pipe, but has little effect on biomass, doesn't make magnitude gap. Adopting a gradual manner chlorination disinfectant studied the role of biofilm disinfection. With the concentration of free chlorine in the water increased to 0.5mg/L gradually, the biomass of the biofilm with the increase of free chlorine shows linear downward trend and the biomass reduced by about 90%. More free chlorine in the water makes a smaller decrease of biomass. The colony morphology difference in and out of water indicates that biofilm is the main source of bacteria suspension. Residual chlorine can reduce the biomass on biofilm, and also kill micro-organisms into the water. Long duration, high concentration of organic content and individual tube sections excessive consumption of disinfectants are the main reason that made significant microbial increase in water. To ensure water bio-safety, besides the usage of disinfectants, it also needs to reduce the hydraulic retention time and the amount of the organic matter in water, and replace or maintain the pipeline which consumes too much disinfectant.