标题: | 表面水处理之问题藻种分析及加药对其去除之影响 Analysis of problem alages in surface water treatment and effect of chemical dosing on their removal |
作者: | 王文美 Wang, Wen-Mei 黄志彬 Huang, Chih-Pin 环境工程系所 |
关键字: | 水处理;藻类;前氧化;混凝;water treatment;algae;preoxidation;coagulation |
公开日期: | 2010 |
摘要: | 低浊高藻原水常出现于以水库为主要水源之水场原水中,由于藻类比重太低而无法有效的藉由混沉程序去除,因而加重净水场过滤单元操作负荷,甚至阻塞无法出水。前氧化结合混沉程序常被采用来去稳定且移除水中藻类,但原水中之针状或条状藻在净水场砂滤程序前很难有效被去除,导致这些藻类阻塞于滤池中,阻碍滤池的操作而致反洗频率增加,因此前处理加药程序(前氧化及混凝)之最适化为提升藻类去除效率之关键。 本研究调查宝一水库不同季节之优势藻种及水质特性与宝山给水场沉淀及过滤单元之问题藻种。此外,以宝一水库原水配制特定藻类数量水样进行前氧化搭配混凝程序实验,探讨加氯前氧化(次氯酸钠及二氧化氯)对藻类细胞特性(藻体结构、叶绿素a与藻类破损程度)之影响,并瞭解前氧化搭配不同混凝剂(聚矽酸铁及硫酸铝)对含藻原水之混沉效能及上澄液过滤性之影响。 研究结果显示,水库优势藻种受气候影响而变化,气温较低时,优势藻种主要为小环藻、舟形藻、沼泽颤藻、针杆藻及盘星藻;气温较高时,水中藻类多以小环藻、四角藻及裸藻为主。水场净水处理单元之问题藻种多为不易被混沉移除且容易堵塞于过滤池之小环藻、盘星藻、舟形藻、沼泽颤藻、针杆藻及直链藻等藻类。 在氧化程序中,次氯酸钠与二氧化氯氧化均能破坏藻类细胞,致使藻类活性降低,提升藻类之沉降性,因二氧化氯氧化对藻类之破坏性较次氯酸钠氧化强,故二氧化氯提升藻类沉降性之成效优于次氯酸钠。当藻类活性降低时,水中叶绿素a浓度会减少,且藻体细胞完整性变低且受损数量增多。此外,加氯氧化时,因二氧化氯氧化力强而导致加氯后藻类破裂致使芳香族蛋白质大量溶出,且水中天然有机物(类腐植酸及黄酸)之浓度亦降低。在加氯前氧化结合混凝程序上,加氯前氧化可提升低浊含藻原水之混沉及过滤效能,在硫酸铝混凝条件下,二氧化氯前氧化对原水混沉效能及上澄液过滤性之提升成效优于次氯酸钠前氧化,而搭配二氧化氯或次氯酸钠前氧化对聚矽酸铁混凝效能之提升差异不大。 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 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. Therefore, the optimum pretreatment, such as oxidation and coagulation, is the key to improve the removal performance in algae by water treatment plants. In this study, the characteristics of dominant algae and water quality in raw water from Bao-San first reservoir were investigated in different seasons. The species of problematic algae in the sedimentation and filtration process of Bao-San WTP was also investigated. In addition, the raw water taken from Bao-San first reservoir was concentrated to the desirable algal concentration in order to carry out the experiments of pre-oxidation combined with coagulation. The effects of pre-chlorination by NaOCl and ClO2 on the characteristics of algal cell (i.e., algal structure, chlorohyll a and cell integrity) before and after pre-chlorination was studied. It is simultaneously estimated that the effect of pre-chlorination coupled with coagulation by different coagulants (i.e., Alum and Polysilicate iron (PSI) on the performance of coagulation/sedimentation and sand filtration for algae-laden water treatment. The results have shown that the dominant algae of reservoir vary with the seasons. During fall and winter seasons, Cyclotella, Navicula, Oscillatoria, Synedra sp., and Melosira are in full bloom, while Cyclotella, Tetraedron, and Euglenophyta bloom in the spring and summer seasons. The problematic algae species existing in the sand filter include Cyclotella, Pediastum, Navicula, Oscillatoria, Synedra sp., and Euglenophyta. In oxidation, algal cells can be destroyed by NaOCl and ClO2 oxidation as a result of the reduced activity of algae accompanied by the increased settleability. Algal cells have been undergone more strong damage by ClO2 than by NaOCl treatment thereby improving the settleability of algae better. When the activity of algae reduces, the concentration of chlorohyll a was decreased along with the reduced quantity in integrated algal cell and the increased quantity in impaired algal cell. Furthermore, the ratio of various dissolved organic matter (DOC) in raw water was not changed obviously after chlorination with NaOCl and ClO2, while only the increased aromatic protein along with reduced natural organic matter (i.e., humic substance-like and fulvic acid-like) was found after ClO2 oxidation of raw water due to the stronger oxidation ability of ClO2. In pre-chlorination/coagulation of algae-laden water with low turbidity, the performance of coagulation/sedmentation and filtration can be effectively improved by pre-chlorination. For alum coagulation, the improvement in the performance of coagulation/sedimentation and the filterability of supernatant by ClO2 pre-treatment is superior to that by NaOCl pre-treatment. However, for PSI coagulation, NaOCl has the similar performance to ClO2. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT079819508 http://hdl.handle.net/11536/47404 |
显示于类别: | Thesis |