活性碳應用於水中全氟與多氟烷基物質吸附效率之評估

Abstract

隨著全球對環境保護與資源永續利用的重視，聯合國永續發展目標（Sustainable Development Goals, SDGs）第6項：「確保所有人都能享有水與衛生及其永續管理」已成為各國水資源治理的重要方針。水資源的安全與衛生是當代關鍵議題，而新興污染物的廣泛流布，對環境與公共健康構成潛在風險。傳統自來水處理程序的目的為去除雜質以達到水質標準，但卻無法有效去除全氟與多氟烷基物質（Per- and Polyfluoroalkyl Substances, PFAS）等新興污染物，因此多種處理技術被廣泛討論以降低飲用水中PFAS濃度。其中活性碳吸附因其高去除效率、不產生副產物、操作簡便、成本相對較低廉等優勢，且無論粉狀或粒狀活性碳皆展現良好吸附性能，被認為是可行的PFAS解決方案。 本研究以實驗室規模探討活性碳對四種代表性PFAS（PFBS、PFHxS、PFOA與PFOS）的吸附行為，並比較椰子殼與煤質兩種材質活性碳之處理效率。分析方法參考國家環境研究院公告之標準檢測方法「水中全氟與多氟烷基物質檢測方法－液相層析串聯式質譜儀法（NIEA W542.52B）」進行調整。另外，對於PFAS檢測分析前處理方式之固相萃取（Solid phase extraction, SPE）亦進行優化測試比較。實驗設計結合吸附動力學、等溫吸附模型與快速迷你管柱試驗（Rapid Small Scale Column Test, RSSCT），先於Milli-Q水（二次去離子水）中探討活性碳對PFAS吸附之模型，進一步應用RSSCT，分別在Milli-Q 水和實場採樣的快濾池清水進行額外添加固定濃度之PFAS後，使用粒狀活性碳（Granular Activated Carbon, GAC）填充之迷你管柱吸附，透過PFAS貫穿曲線評估GAC在水中吸附PFAS的表現。 本研究結果顯示，前處理經過初步酸化的樣本，使用Oasis WAX固相萃取管匣進行萃取，且管匣不再經過0.1%甲酸潤洗，可獲得四種PFAS最佳SPE回收條件（回收率均超過75%）。接著進行動力吸附與等溫吸附實驗，著重於討論椰子殼活性碳（TAC-C）與煙煤活性碳（F400）對PFAS之吸附效能。發現在Milli-Q水中進行吸附模型擬合下，對於所有四種PFAS化合物，使用TAC-C作為吸附劑的結果符合擬二級吸附動力學。相反，使用F400作為吸附劑的結果則符合擬一級吸附動力學。總結等溫吸附之模型結果，得出在Milli-Q水中使用Freundlich等溫吸附模型能更好地描述TAC-C和F400對PFAS的吸附，反應了異質介面相互作用。 透過操作RSSCT兩周的實驗結果，在Milli-Q水中，TAC-C較早出現貫穿，尤其是對PFBS和PFOA。而F400表現出最佳的整體吸附能力，對大多數PFAS的貫穿維持在10%以下。相比之下，在實場快濾池清水中，PFAS吸附能力由於其他天然有機物的競爭而顯著降低GAC的吸附成效。以TAC-C而言，在25,000個濾床體積時除了PFOS以外，皆出現90%貫穿現象；F400在大約15,000個濾床體積四種PFAS已出現30%貫穿現象；TAC-Q作為與TAC-C來自相同品牌之煤質活性碳，其貫穿曲線在PFBS出現超出初始濃度之貫穿現象，然而其餘PFAS的貫穿程度皆低於椰子殼活性碳。 這些結果顯示水體基質效應對PFAS吸附行為中的重要性，並凸顯了煤質GAC的優異吸附性能。實際應用必須考慮到背景污染物的競爭，可能會加速GAC飽和並降低處理效能。以上結果確立煙煤質活性碳整體吸附效能優於椰子殼活性碳，且對長鏈PFAS（PFOA與PFOS）之去除率高於短鏈PFAS（PFBS與PFHxS）。本研究結果可作為未來臺灣淨水場採用活性碳處理PFAS之參考，並提供具體建議以協助實踐SDGs第6項永續發展目標，確保民眾飲水安全。

With growing global attention to environmental protection and sustainable resource management, the United Nations Sustainable Development Goal (SDG) 6 - “Ensure availability and sustainable management of water and sanitation for all” - has become a key policy direction for water resource management across nations. The safety of water resources remains a critical issue, particularly as the widespread presence of emerging contaminants poses potential risks to the environment and public health. Conventional drinking water treatment processes are designed to remove impurities to meet the water quality standards. However, they are ineffective in removing emerging contaminants such as Per- and Polyfluoroalkyl Substances (PFAS), and therefore, various treatment technologies have been proposed to reduce the concentration of PFAS in drinking water. Various treatment methods have been developed for different PFAS types, among which activated carbon (AC) adsorption stands out for its high removal efficiency, lack of harmful byproducts, operational simplicity, and relatively low cost. Both powdered (PAC) and granular (GAC) activated carbon have demonstrated excellent adsorption performance and are considered feasible solutions for controlling PFAS in drinking water. In this study, the adsorption behavior of activated carbon on four representative PFAS (PFBS, PFHxS, PFOA, and PFOS) was investigated on a laboratory scale, and the treatment efficiencies of activated carbon on two materials, coconut shell and coal, were compared. The analytical method has been adjusted with the standard method “Method for Determination of Per and Polyfluoroalkyl Substances in Water by Liquid Chromatography/Tandem Mass Spectrometry (NIEA W542.52B)”. In addition, the analytical pretreatment method, solid phase extraction (SPE), was optimized to compare the analytical performance of the PFAS studied. The experimental design integrated adsorption kinetics, adsorption isotherms in Milli-Q water (deionized water) to discuss the adsorption models, and further applied in the Rapid Small Scale Column Test (RSSCT) to determine the PFAS adsorption characteristics and parameters in Milli-Q water. Following this, the RSSCT assessed the breakthrough of a spiked concentration of PFAS in both Milli-Q water and rapidly filtered water collected from a drinking water treatment plant. After the addition of a fixed concentration of PFAS to Milli-Q water and field rapid filtered water, the adsorption operation was carried out using a mini column filled with granular activated carbon (GAC) to evaluate the performance of GAC in the adsorption of PFAS in water by the PFAS breakthrough curve. The results of the study showed that the best SPE recovery conditions for all four PFAS (recovery of more than 75%) were obtained when the samples, which were initially acidified in the pre-treatment, were extracted using Oasis WAX cartridges, which were no longer lubricated with 0.1% formic acid. Kinetics and equilibrium isotherm adsorption experiments were then conducted, focusing on the adsorption efficacy of PFAS adsorption with coconut shell activated carbon (TAC-C) and bituminous activated carbon (F400). In Milli-Q water, the results using TAC-C as adsorbent were consistent with the proposed pseudo-second-order model for all four PFAS compounds. On the contrary, the results using F400 as the adsorbent were best described with the proposed pseudo-first-order model. Summarizing the results of isothermal adsorption modeling, it was concluded that in Milli-Q water, the adsorption of PFAS on both TAC-C and F400 could be better described by the Freundlich isothermal adsorption model, which reflects the heterogeneous interactions. By manipulating the RSSCT results conducted for 2 weeks, TAC-C showed an earlier breakthrough in Milli-Q water, especially for PFBS and PFOA, whereas F400 showed the best overall adsorption capacity, maintaining breakthrough below 10% for most PFAS. In contrast, the adsorption efficacy of GAC was significantly reduced by competition from other naturally occurring organic matter (NOM) in the field rapid filtered water. In the case of TAC-C, 90% breakthrough was observed at 25,000 bed volumes except for PFOS, while F400 showed 30% breakthrough at about 15,000 bed volumes for the four types of PFAS; TAC-Q, which is the same brand of coal-based activated carbon as TAC-C, showed breakthrough curves except for breakthrough beyond the initial concentration of PFBS. However, the breakthrough degree of the other PFAS was lower than that of the coconut shell activated carbon. These results highlight the importance of the aquatic matrix effect on PFAS adsorption behavior and underscore the superior adsorption performance of coal-based GAC. The real-world applications must consider the competitive effects of background contaminants, which may accelerate GAC saturation and reduce treatment efficiency. The above results establish that coal-based activated carbon has overall superior adsorption performance compared to coconut shell activated carbon, and achieves higher removal rates for long-chain PFAS (PFOA and PFOS) than for short-chain PFAS (PFBS and PFHxS). The findings of this study can serve as a reference for future adoption of activated carbon treatment for PFAS in Taiwan's water treatment plants, and provide concrete recommendations to support the implementation of SDG 6, ensuring public drinking water safety.