污水在下水道系統中流動時會發生物理、化學與生物的反應，並造成特定組成的改變。而下水道中降解污染物的主要角色是生物膜系統，因此本研究以長21.7m，直徑0.15m的下水道模型廠，經由穩態培養使管壁附著固定生物膜後，分別進行溶氧剖面的量測及批次實驗的水質分析。由實驗結果可探討影響溶氧傳輸的因素﹔同時配合建立的模式以暸解管渠中的水質變化情形。 在溶氧傳輸的研究方面，溶氧要從水體中傳至生物膜內與擴散層厚度有關，流速愈快，擴散層厚度愈薄，溶氧可更容易傳送至生物膜內。除了流速外，水體中的溶氧濃度及污染物濃度都會影響到溶氧的傳輸，水體中之溶氧濃度高或污染物濃度低會有助於溶氧的傳輸。 在水質轉化的研究部份以Activated Sludge Model No.1為依據，建立一個可描述有機碳化合物及氮化合物在下水道中傳輸及轉化的模式。模式內考慮水體中好氧生長、生物膜內缺氧生長、溶解性有機氮的氨化、捕捉性有機氮的水解等程序。並同時配合實驗的結果以確定模式的可靠性。由實驗及模擬的結果均顯示溶氧受到起始污染物濃度及流速的影響最大。起始污染物濃度愈高，所消耗的溶氧量愈多，因此須較長時間來達到曝氣量與被生物利用量之平衡；流速快則再曝氣作用明顯，溶氧濃度也愈容易增加。且起始污染物濃度愈高，生物膜內微生物對污染物的降解速率也愈快。流速增加時，各種成份的傳輸情形會較好，相對在管渠中的停留時間短，因此對降解污染物濃度的成效並不理想；對提高溶氧則有良好之效果。 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.
