| dc.description.abstract | Many chemical, physical and biological transformations of wastewater would take place in sewer system and caused significant changes in the compositions during transportation. Biofilm played the main role in degrading pollutants in the sewer system. The biofilm was cultivated in a 21.7m long pipe, with a diameter of 0.15m model sewer model plant. Under stable condition, the biofilm was securely attached on the pipe botton, so the dissolved oxygen profile could be measured and water quality analysis could be proceeded in the batch experiments. The factors that effect the transportation of dissolved oxygen could be explored from the experiments results. How does water quality change in the pipe by established model could be understood at the same time.
In the study of oxygen transfer, the dissolved oxygen transfered from bulk water to biofilm was directly related to the thickness of diffusion layer. The faster the flowing velocity and the thinner diffusion layer thickness is, the more easily oxygen transfered into the biofilm. Other than the flowing velocity, the concentration of the dissolved oxygen and the concentration of the pollutants all affected the transportation of the dissolved oxygen. The higher concentration of dissolved oxygen in water or the lower concentration of the pollutants all favor the transportation of dissolved oxygen.
A model based on the Activated Sludge Model No.1 was established to simulate the transportation and transformation of carbon compounds and nitrogen compounds in the sewer system. Processes of aerobic growth in bulk water, anoxic growth in biofilm, ammonification of soluble organics nitrogen, hydrolysis of entrapped organic nitrogen etc. was considered in the model. In order to explore the fitness between the model prediction values and the experimental values, these two values were compared.
The experimental and simulated results both indicated that dissolved oxygen was affected mostly by the concentration of the pollutants and flowing velocity. The higher concentrations of the pollutants comsumed more oxygen; therefore, it took longer time to reach the balance of aeration and the utility by organisms. The faster the flowing velocity was, the more significant the reaeration effects were. The concentration of dissolved oxygen also increased easily when the concentration of initial pollutant was high, the microbial degrading rate of the pollutants in biofilm could increase. The transportation ability of each component increased with the flow velocity increased that resulted in the dissolved oxygen increased. On the contrary, pollutants degrading performance decreased with the short retention time in the pipe. | en_US |