利用電場奈米過濾及超過濾去除鐵錳砷

Remove Iron,Manganese and Arsenic by Electro-Nanofiltration and Ultrafiltration

許穗蒨(Sui-Chien Hsu)

指導教授 ： 莊清榮

中原大學/工學院/化學工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100945

摘要

摘要
在台灣地區，地下水是公共給水的重要水資源之一，而地下水普遍常見鐵和錳兩種元素，造成處理上的困擾，大多是先將溶解性的二價鐵及二價錳氧化成非溶解性的三價鐵及四價錳，而後再進行固液分離。而砷則是台灣西南部及東北部地下水或井水中常見的天然汙染物，因砷的劇毒性，若長期飲用含有砷的地下水，會對人體健康有很大的危害，因砷的體積較小去除不易，需藉由混凝程序或吸附等方法來去除。
近年來，因淨水品質的提升，國內外許多淨水場陸續採用薄膜程序的方式來處理水質，且薄膜系統有較為節省空間之優點，不僅在淨水工程上，也可應用在食品工業及生化等方面。本研究以奈米過濾及超過濾方式，過濾含有高濃度的鐵溶液、錳溶液、鐵錳混合溶液以及五價砷溶液，並且在膜面的兩端施加不同強度的電場，分析離子在電場作用下的去除效率及濾液通量的提升，探討在不同進料組成、溶液條件、電場強度等操作條件對過濾效能之影響。
有機薄膜大多含有可解離之官能基，因此溶液性質對膜面界達電位之影響甚大，而膜電性與溶質間之靜電作用力也常是影響離子分離效能的重要因素，NF-270及兩種孔洞大小的UF膜材之膜面界達電位皆隨溶液pH值的提高而增加。以NF-270過濾單一鐵、錳及混合溶液時，其壓力對離子阻擋率影響不明顯，但三者的過濾通量隨著pH上升而有下降的趨勢，離子阻擋率則有些微的上升，過濾後濾液鐵濃度皆可符合飲用水標準的0.3 mg/L，而錳的濃度還是偏高，無法低於標準0.05 mg/L。而後以RC-10kDa的UF薄膜搭配不同強度的電場，過濾鐵錳混合溶液，過濾通量因施加一高電場強度而有明顯的上升，不管是否有施加電場，鐵的濾液濃度已經符合標準，錳則需在較高pH值下，其去除率才能有效提高。
在砷的部分，先以30及10 kDa的UF薄膜過濾在pH6、進料為1 mg/L下過濾五價砷溶液，30 kDa的薄膜因為孔洞較大，對於五價砷幾乎沒有去除效果可言，10 kDa的去除效果隨著施加電場強度的增加而上升，因為五價砷在此環境下帶負電，施加電場後遠離膜面而提高去除率。調高五價砷溶液的pH值，使五價砷帶有更多的負電，再經NF-270過濾，有顯著的去除效果，施加電場後，不僅提高過濾通量也使阻擋率增加。

關鍵字

鐵 ； 砷 ； 奈米過濾 ； 超過濾 ； 錳

並列摘要

ABSTRACT
In Taiwan, the groundwater is one of the important water resources for public water supply. Iron and manganese are usually found in the groundwater and the corresponding problems caused by them are highly concerned by the water facility. Iron and manganese are generally removed by oxidation first and then separated by filtration processes. Another natural contaminant may appear in some area of Taiwan groundwater is arsenic. Because arsenic is highly toxic and very small, coagulation or adsorption coupled with other methods generally are required to remove it.
Recently, membrane processes have been widely used for water treatment to improved water quality. In order to investigate the feasibility by using membrane filtration to purify the groundwater containing iron, manganese and arsenic contaminant, nano-filtration and ultra-filtration were applied in the study to filter the solution containing the contaminants mentioned above. Electric field was imposed on the filter to examine the effect of the external force on the enhancement of the filtration performance.
An nanofiltration membrane, NF-270, and two UF membranes, RC10 kDa and 30 kDa were used for the experiments. The feed solution concentration were prepared as 5mg/l iron or manganese. Experimental results from NF-270 membrane showed that under the operating pressure ranging from 3 to 5 bar the rejections of iron and manganese are higher than 94% and 96%, respectively and are only slightly effected by the applied pressure and the pH used in a range of 6 to 10. However, the filtration flux is decreased obviously with the increased pH. The iron concentration in filtrate can meet drinking water standard of 0.3 mg/L, while the manganese concentration is still not less than the standard 0.05 mg/L. When the feed is an iron and manganese mixed solution, the iron rejection is obviously higher than that from solution only containing iron, while the manganese rejection is nearly the same as that from single manganese solution.
Experimental results by using RC-10 kDa membrane to filter iron and manganese mixed solution showed that the pH and applied electric field strength are only give a very slight effect on the high rejection of iron. The iron concentration in the filtrate meet the drinking requirement. On the contrary , the manganese rejection depend on the pH and electric field strength, the higher pH and electric field strength applied the higher rejection obtained.
As for arsenic filtration, RC-30 and 10 kDa UF membranes were first used to filtrate 1 mg/L pentavalent arsenic (As(V)) solution under pH6. Experimental results showed that the 30 kDa membrane gives a very low rejection even under a high electric field strength as 4000 V/m. Although the 10 kDa membrane can provide a higher rejection of As(V) as 82% when electric field strength is 4000 V/m, the As(V) concentration in filtrate is still not meet the drinking water quality standard, Taiwan.
When the groundwater containing As(V)<3mg/L is filtrate by NF-270 membrane with electric field, under the conditions of pH larger than 8 and electric field strength higher than 4000 V/m the filtrate will has a As(V) concentration lower than the drinking water standard.

並列關鍵字

Manganese ； Nano-filtration ； Arsenic ； Ultra-filtration ； Iron

參考文獻

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