低濁含藻原水最適處理藥劑及濾材之研究

Abstract

低濁高藻原水常出現以水庫為主要水源之水廠原水中，由於藻類密度太低而無法有效的藉 由混沉程序去除，加重淨水場過濾單元之操作負荷，甚至阻塞無法出水。前氧化結合混沉程序 常被採用來去穩定且移除水中藻類，但原水之針狀或條狀藻是很難有效在淨水場砂濾程序前被 去除，導致這些藻類阻塞於濾池中，阻礙濾池的操作而致反洗頻率增加，再加上濾池中微生物 會以此藻類為食物，於濾池內增生，此會導致濾池內細菌量增加及生物膜的生長。為了避免這 些問題藻類流進濾池，傳统混凝及過濾操作技術勢必要有所改良。因此本計畫首先以最近環保 署公告之淨水用藥聚矽酸鐵(PSI)，以提昇藻類混凝效率為目的加以改良其成份比，接著研究 不同前氧化劑及加藥量對問題藻類於混沉過濾程序移除之影響，最後並評估面臨問題藻類出現 時之濾池使用傳統濾料及抗生物濾料之操作差異。 首先，在不同季節下原水中各種問題藻類將在現地收集且藉由光學顯微鏡鑒定，並以實驗 室製備之PSI 混凝劑，來評估聚鐵型態物種對含藻原水混凝效率及混沉後上澄液過濾效能之影 響，並與Alum 作比較。此外，將評估前氧化結合PSI 及Alum 混沉程序對問題藻類去除之效 率。最終，抗生物濾料（錳砂）及傳統濾料（即石英砂）之兩種模廠管柱將同時過濾實場沈澱 出流水，並將進行兩種濾料之過濾及反洗試驗。本研究結果將作為自來水事業單位建立混凝及 過濾處理低濁高藻原水最適化操作策略之參考。

Low turbidity along with abundant algae is frequently found in raw water taken from reservoirs by water treatment plants (WTPs). Because the density of the algae is too low to be effectively removed from the water by coagulation-sedimentation, the burden on the operation of the filtration unit in the WTP is significantly increased. In addition, the algae may clog the filter and slow down or stop the filtration. While a hybrid pre-oxidation/coagulation-sedimentation process is commonly adopted to destabilize and remove the algae in raw water, it is difficult to effectively remove strip or needle algae before the sand filtration process in the WTP because the setting rate of these algae is rather poor. As a result, the filter is easily clogged with these algae, which significantly impedes its operation and causes an increased frequency of backwashing. Meanwhile, microbial hyperplasia may occur in the filter because microorganisms within the filter can feed on the algae cells, resulting in an increase in the quantity of bacteria and biofilms. To prevent the algae from flowing into the filter, the traditional coagulation and filtration technology needs to be improved. Therefore, this study aims to improve the coagulation of algae through preparing the polysilicate iron (PSI) coagulant, a new coagulant approved by the EPA. In addition, the effects of different pre-oxidants of various dosages on algae removal using the coagulation-sedimentation process will be investigated. Furthermore, the differences in the operation of filters equipped with anti-microbial and traditional filter media in the presence of algae will be evaluated. In this study, various problem algae in raw water during different seasons will be collected on-site and identified using a high-resolution optical microscope. The PSI coagulants will be prepared in the lab, which will be used to evaluate the effects of polyferric species and alum speciation on the coagulation of algae-rich raw water, and determine the filtration performance of the supernatants after coagulation-sedimentation. The removal efficiency of the algae by PSI and alum coagulation coupled with a pre-oxidation process will be determined by counting residual algae after coagulation. Then pilot-scale filtration columns equipped with anti-microbial filter media (i.e., manganese sand) and traditional filter media (i.e., quartz sand) will be simultaneously operated to filtrate the effluents of sedimentation unit of WTP, followed by filtration and backwashing experiments of both media. The results of this study will help water utilities to establish optimization strategies for coagulation and filtration operation to treat low turbidity water with abundant algae.