以幾丁聚醣及鋁鹽混凝劑處理高濁度原水之研究

Treatment of extremely high turbid water by chitosan and aluminium salts

陳富鈴(Fu-Ling Chen)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01044

摘要

面對遽變的氣候、特殊的地形及集水區的過度開發，暴雨產生高達數千至上萬高濁度原水的頻率逐年增加，對於主要以地表水為水源之自來水事業單位而言，提供足量符合規範的安全飲用水成為暴雨期間嚴峻之考驗。鋁鹽混凝劑增加使用將提高污泥產生量，但會造成淨水單元無法負荷，必須採取減量供水或甚至關廠停水的措施；此外亦會增加水中鋁含量而提高健康之風險。故如何提升混凝劑於高濁度原水之處理效能及降低水中鋁含量，為一值得研究之議題。
本研究以實驗室配製之10000 NTU人工原水及梅姬颱風期間直潭淨水場取水口5000 NTU原水為研究對象，以鋁鹽（多元氯化鋁、硫酸鋁）及天然高分子聚合物幾丁聚醣為混凝劑進行酸鹼度、殘餘濁度、污泥體積及溶解鋁之分析，藉以評估不同混凝模式之整體效能。由10000NTU人工原水試驗所得之結果顯示，鋁鹽混凝劑(0.2-60 mg/L as Al)會隨添加劑量增加而提高污泥體積量至60-70 ml/L，並使水中殘留溶解鋁含量超過300μg/L，其中多元氯化鋁混凝劑之濁度去除效果優於硫酸鋁混凝劑。幾丁聚醣隨著添加濃度增加產生的污泥體積量能維持約40 ml/L，並降低水中溶解鋁至小於50 μg/L，濁度去除效果與多元氯化鋁相近。但三者皆無法因增加藥劑量而使水中殘餘濁度將低至小於10 NTU。複合試驗分析10000 NTU人工原水。使用幾丁聚醣搭配固定濃度（0.2 mg/L、0.5 mg/L）鋁鹽之混凝效果良好，於較低添加藥劑量時即可使水中殘餘濁度濁度小於10NTU，並維持不變之污泥體積量及降低水中殘留溶解鋁至約25 μg/L。若改使用鋁鹽搭配固定1 mg/L幾丁聚醣濁度去除效果與單獨使用鋁鹽之結果相似，但所需加藥量相對較低，若持續加藥無法再降低殘餘濁度值，而污泥體積量及殘留溶解鋁亦會隨藥劑量增加而提高，水中溶解鋁之含量約200 μg/L，相較單獨使用鋁鹽為混凝劑時低。取用梅姬颱風期間5000 NTU高濁度原水進行混凝模式試驗，其結果趨勢與人工高濁度原水相似，除因暴雨沖刷產生較易沉降之顆粒，致使所有試驗之濁度去除效果未呈現明顯差異外，污泥產生量與殘留溶解鋁之結果趨勢與10000 NTU人工原水相同。
綜合上述結果可知，以幾丁聚醣搭配少量鋁鹽混凝劑，對於高濁度原水具有良好濁度去除效果，能產生較低且維持不變之污泥產量，於暴雨期間減輕淨水處理單元負荷，增加供水效能；並降低原水中鋁含量，避免其過高而提高致病風險。

關鍵字

幾丁聚醣 ； 混凝劑 ； 溶解鋁 ； 高濁度原水 ； 污泥

並列摘要

Because a rapidly changing climate, special topography and over-exploitation of catchment areas, the frequently high turbidity raw water is caused by heavy rains and increase year by year. Therefore, for water supply units with surface water as their major water source, a supply of sufficient safe drinking water in compliance with provisions has become a severe challenge during storms. The utilization of aluminum salt coagulant currently results in increased sludge output, leading to excessive loads for water purification units and reducing or even cutting-off water supplies. Increased aluminum salt coagulant will increase the aluminum content in water and thus bring more health risks. Hence, it is important to improve the treatment efficiency of coagulants in high turbidity raw water and reduce the aluminum content in water.
In this study, 10000 Nephelometric Turbidity Unit (NTU) of artificial raw water was prepared in a laboratory and 5000NTU of raw water was sampled from the water intake of Zhitan Water Treatment Plant during Typhoon Maggie, respectively. The aluminum salt (Polyaluminum Chloride, aluminum sulfate) and natural polymer chitosan were used as the coagulants. Experiments with varying operational parametersof pH, residual turbidity, sludge volume and dissolved aluminum analysis were evaluated for the overall effectiveness of different coagulation models.Results from the test with 10000 NTU artificial raw water showed that addition of aluminum salt coagulant would increase the sludge volume to 60-70ml/L and cause the residual dissolved aluminum content in water to exceed 300μg/L. The Polyaluminum Chloride coagulant revealed better turbidity removal performance than the aluminum sulfate coagulant. Sludge volume generated by chitosan could be maintained at about 40 ml/L, and dissolved aluminum in the water could be reduced to less than 50μg/L. Turbidity removal efficiency of chitosan was similar to that of aluminum chlorohydrate. But none of the three could reduce residual water turbidity to less than 10 NTU with increased dosage.When chitosan was combined with fixed-concentration (0.2mg/L, 0.5mg/L) aluminum salt to treat 10000 NTU of artificial raw water, the residual turbidity and residual dissolved turbidity reduced to less than 10 NTU and 25μg/L, respectively, at low additive dosage, while sludge volume unchanged. When aluminum salt was combined with chitosan with a fixed concentration of 1mg/L, the turbidity removal efficiency was similar to that of chitosan alone. However, it only required a relatively low dosage. In addition, sludge volume and residual dissolved aluminum would increase with increased dosage while the content of dissolved aluminum in water was 200 μg/L. This result was lower than that of aluminum salt alone. Test results of the high turbidity raw water coagulation model during a typhoon were agreement with those of artificial high turbidity raw water. Nevertheless, the turbidity removal efficiency did not show significant difference because erosion of heavy rainfall produced particles more likely to settle, resulting in the trend of generated sludge volume and residual dissolved aluminum being the same as that of 10000 NTU artificial raw water.
From the above results, it can be concluded that chitosan combined with a small amount of aluminum salt coagulant has good turbidity removal effect on high turbidity raw water. It can produce low sludge output which remains unchanged, thereby reducing the load for water purification and treatment units during storms. Also, increasing water supply efficiency, reducing the aluminum content in raw water and avoiding increased risk of illness caused by excessive aluminum content can be achieved by combination of chitosan and aluminum salt coagulant.

並列關鍵字

chitosan ； coagulant ； dissolved aluminum ； high turbidity raw water ； sludge

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行政院環境保護署網站: http://www.epa.gov.tw/.

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