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The Study on The Biodegradation of Natural Organic Matters in Slow Sand Filters
|關鍵字:||Biodegradation;生物降解;Slow sand filter;Humic acid;p-hydroxy- benzoic acid;ozonation;慢砂濾;腐植酸;對羥基苯甲酸;臭氧化||出版社:||環境工程學系||摘要:||
飲用水水源中常含有天然有機質(Natural Organic Matters , NOMs)，這些天然有機質在傳統的淨水處理中去除不易，原水水源中所含的NOMs可能會在淨水處理流程的加氯消毒單元中形成消毒副產物(Disinfection By-Products, DBPs)，而不同的淨水程序也會影響加氯消毒物產物。
傳統淨水流程對於天然有機物並無法有效的去除，導致消毒程序中產生DBPs 而危害飲用水的安全。本研究對上述議題進行以下的探討。首先，探討生物降解對水中NOMs消長的影響及影響生物降解的因素；其次，探討活性碳三明治濾床(Granular Activated Carbon Sandwich Filter, GACSF)對於傳統慢砂濾床(Slow Sand Filter, SSF)缺點的改善及效益；最後則探討臭氧氧化程序對NOMs生物降解性的影響。研究中採用PHBA (p-hydroxy-benzoic acid)及HA (Humic Acid)做為NOMs的人工模擬基質，HA為NOMs的主要成份，而PHBA則為HA成份之ㄧ，以此做為基質較易顯示生物降解的過程。實驗中的分析項目包括以HPLC量測基質濃度，以UV吸光度(波長為254 nm)偵測不飽和雙鍵，並量測DOC (Dissolved Organic Carbon)及THMFP (THM Formation Potential)，另以UF (Ultrafiltration)來做分子量的篩選。本研究亦以呼吸儀量測基質臭氧化前後的生物可降解率。
實驗結果顯示，SSF的生物降解主要是發生於砂層深度 0 ~ 50 cm之處，且水力負荷(m3/m2-day)越低，生物降解越明顯。超過此一砂層深度後，DOC的去除則是受到砂層深度的影響。而使用GACSF的系統於運轉初期即能有效的去除DOC，縮短SSF系統啟動的生物遲滯期，得以改善SSF系統運轉初期水質不佳的問題。此外，GACSF與添加人工植菌(Bio-GACSF)兩組試驗結果顯示，經生物降解後的水質其THMFP出現最低值，顯示添加GAC對於THMFP有良好的控制功效。而PHBA及HA經臭氧化後，對於DOC的去除並不明顯，而當O3/DOC的劑量大於 1.1 mg O3/mg DOC時即會抑制PHBA的生物降解，因此添加臭氧的劑量需加以控制。而添加人工植菌對於PHBA及HA兩種基質在DOC的去除都有顯著效果，可縮短遲滯期且達到DOC處理較佳的效能。此外，利用UF篩選HA臭氧化及生物降解後的分子量(MW)分布的實驗結果顯示，MW分佈在 5 ~ 1 K dalton之間的HA以臭氧處理並添加人工植菌對DOC的去除率最高。HA經臭氧化後， THMFP/DOC 為 293 μg/mg，而再經過生物降解後，THMFP/DOC下降至 75 μg/mg，說明NOMs經臭氧化併同生物降解後，對於DBPs的控制相當顯著。
The natural organic matters (NOMs) present in the raw water can not be easily removed in the traditional water treatment process, especially the small amount of dissolved organic carbon (DOC). The source of raw water and the process of water treatment significantly influence the formation of disinfection by-products (DBPs). The biological process in the drinking water treatment process has many advantages, such as reducing of disinfection by products (DBPs) in the treated water and reducing the re-growth of microorganisms in the distribution system. It can also reduce the chlorine consumption and biodegradable matter.
This study focused on the biodegradation of NOMs in the water treatment process. The DOC removal and other operating parameters were determined with two different processes, the slow sand filter (SSF) and the granular activated carbon sandwich filter (GACSF). Furthermore, this research investigated the effect of ozonation on the biodegradation of NOMs. The simulated target substrates were p-hydroxy-benzoic acid (PHBA) and humic acid (HA). HA is the main constituents of NOMs, and PHBA is one of the identified composition of HA.
The results revealed that the biodegradation mainly occurred in depth of 0 ~ 50 cm within SSF column. And increase in the overflow loading (m3/m2-day) decreased the biodegradation effects. The DOC removal efficiency was affected by the depth of sand. The GACSF system could effectively eliminate DOC and shorten the lag phase for DOC removal during the initial stage of the SSF system. According to the experimental results of GACSF and Bio-GACSF (augment microorganisms into the GACSF column) tests, the THMFP was down to the lowest value in the Bio-GACSF system. These results indicated that presence of GAC could effectively control the THMFP. The ozonation of PHBA and HA did not result in the significant DOC removal. The biodegradation of PHBA was inhibited when ozone dosage over 1.1 mg O3/mg DOC, it suggested that ozone dosage should be well controlled to avoid the inhibition on the DOC biodegradation. Seeding of microorganisms into the sand columns could apparently promote the DOC removal efficiency, shorten lag phase and attain a better treating performance. By analyzing the molecular weight (MW) distribution of ozonated and un-ozonated HA with ultrafiltration (UF), HA with MW 1 ~ 5k dalton demonstrated the best DOC removal efficiency. The THMFP/DOC ratio of un-ozonated and ozonated HA were 293 μg/mg and 75 μg/mg, respectively. It also suggested that the control of DBPs could be achieved by treating NOMs with both ozonization and biodegradation processes.
|Appears in Collections:||環境工程學系所|
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