| 摘要: | 本研究目的係探討不同原水濁度，對平鎮淨水場高速膠凝平板式污泥毯澄清池（以下簡稱澄清池）處理效能之影響。研究內容以收集統計90~94年間，淨水場原水水質數據，了解原水濁度特性及分佈趨勢；並統計近五年澄清池出水達成率，就水質數據及現場操作參數等因子，討論其與澄清池效能的相關性；另一方面探討不同濁度下，澄清池出流水濁度未符合場內自訂標準的原因；最後以實場試驗，在低濁度下（5~10 NTU）改變原水取水程序形成泥毯，評估形成澄清池泥毯及改善出水濁度之可行性。 由統計資料可知，原水濁度除夏、秋季颱風暴雨期間外，有九成以上都在200 NTU以下，其中5~15 NTU區間之濁度分佈比例最高，約佔45﹪；值得注意的是，原水濁度高低雖呈現季節性變化，但澄清池出水達成率偏低的原因卻與季節性無直接關係。影響澄清池處理功能因子中的上升流速、加藥量及pH值，在實場操作上，均在水力負荷設計值3.12~4.70 m/hr內，而加藥後的pH值維持在7.0~7.5之間，並非直接影響泥毯絮凝優劣的因素；而原水濁度可能是影響澄清池處理效能最關鍵因素，其與污泥毯的形成有較直接的關係，當原水濁度在10 NTU上下時，對澄清池泥毯絮凝的影響最為顯著，使得澄清池出水濁度達成率偏低，僅達76﹪；在15~200 NTU的中等濁度，泥毯可以正常形成，但需注意操作人員因應濁度、處理水量變化的控制；至於颱風暴雨期間的高濁度（大於200 NTU），澄清池的操作主要需考量是排泥問題，而非污泥毯的維持，此時澄清池操作模式只能以減少進流水量因應。 實場試驗部分，由第二原水站抽取後池堰原水約8萬6千噸（濁度約100 NTU），混合石門水庫195出水口原水約48萬噸（濁度約5~10NTU），比例約1：6，改變原水取水程序，形成穩定的中低原水濁度（約分佈在15~30 NTU），可有效形成穩定的泥毯，此時泥毯形成初期濃度約在200 mg/l，穩定之後，約在400~800 mg/l之間，泥毯厚度平均約在2.5m~3m。平均的濁度去除率在87﹪左右，澄清池出水可達到5 NTU以下的要求標準。 The objective of this study was to investigate the effect of raw water turbidity on the performance of the high speed flocculation flat bottom type-sludge blanket clarifier in Pingjan water treatment plant. This study gathered the data of raw water quality of the plant during the periods from 2001 to 2005. The characteristics and distribution of raw water turbidity in relation to the achieving rate of effluent turbidity for the clarifier were discussed. On the other hands, to improve the achieving rate, the main factors which affect the performance of the clarifier, such as water quality, design parameters and operating conditions, were also investigated. Finally, the feasibility of improving effluent turbidity was evaluated by mixing with other influent source to form the sludge blanket when encountering low turbidity (5 to 10 NTU) in the raw water. According to the statistical data, the raw water turbidity was lower than 200 NTU with more than 90% of opportunity, except for the typhoon periods in summer and fall. However, the turbidity range in 5 to 15 NTU had the highest probability to occur (about 45%). The reason for low achieving rate of effluent turbidity, as was observed interestingly, had no concern with the season, though the variations of turbidity in the raw water was seasonal. Moreover, the upflow velocity and pH could maintain practically from 3.12 to 4.70 m/hr and 7.0 to 7.5, respectively, which were consistent with design parameters of the clarifier. The raw water turbidity other than pH and coagulant dosage had directly found to be related to the formation of sludge blanket, which became the key factor for the performance of the clarifier. The sludge blanket could not be formed well and led the achieving rate of effluent turbidity to reach only 76% when the raw water turbidity was 10 NTU approximately. The sludge blanket could be formed normally between 15 and 200 NTU of raw water turbidity, but operators should take care of controlling water quantities accordance with variation of turbidity. As to the high turbidity of raw water for storm weather and typhoon periods (higher than 200 NTU), the strategy of clarifier operation was to decrease the influent flow rate at this time, and the most important consideration was to withdraw sludge instead of forming blanket. In real-plant experiments of changing influent source, the raw water turbidity was increased to the range between 15 and 30 NTU by mixing 480,000 m3 of water from No. 195 water outlet of Shimen reservoir (about 5 to 10 NTU) and 86,000 m3 of that from the secondary pumping station (about 100 NTU). The stable sludge blanket in the clarifier was formed effectively. The concentration of blanket was about 200 mg/L at initial, but would gradually increase to the range of 400 to 800 mg/L with thickness of 2.5 to 3 m at average when reaching stable state. At this moment, the average removal of turbidity was about 87%, and effluent turbidity of the clarifier was lower than 5 NTU which meet the requirement of this plant. |
