利用木屑去除藥物以及防腐物質

Abstract

營養鹽(氮、磷)過量是21世紀環境的一個重要課題，而木屑反應系統，是用來處理硝酸鹽氮的一個自然且便宜的系統，也已開始被實際操作在去除農業污水上。除了過量的營養鹽之外，環境中同時也存在著許多微量有機污染物。因此，為了瞭解這些潛在危害物質在木屑反應系統內的宿命，本研究主要目的為研究八種在自然水體易被檢測到或檢測濃度較高的新興污染物通過木片生物反應系統的宿命並調查八種藥物在木屑反應系統中的去除機制，以及不同條件下，對於藥物去除效果之影響。木屑系統中八種化合物的去除率與化合物密切相關：acetaminophen (ACE, 幾乎完全去除)、caffeine (CAFF, 60-80%)、sulfathiazole (SFZ, 60-80％)、5-methyl-1-H-benzotriazole (TT, 55-80％)、benzotriazole (BT, 35-80％)、carbamazepine (CBZ, 40-60％)、lincomycin (LIN, < 30％)以及ibuprofen (IBU, <10％)。 研究結果顯示，木屑反應系統中，藥物去除機制主要以生物降解及吸附為主。生物降解是ACE去除的主要途徑，而吸附是SFZ，TT，BT和CBZ（分別為Kd = 145.2、35.5、35.6和36.6）在木片生物反應系統中去除的主要機制。以陰離子形式的化合物（如IBU）最不易被吸附，而以中性分子形式存在的化合物（CAFF、ACE、CBZ、TT、BT和LIN）吸附能力隨其KOC值增加而增加。然而，當八種目標化合物同時存在於水相時，會產生競爭吸附，並且所有目標化合物Kd值降低。由於CAFF在木片反應系統中同時具有吸附作用（Kd = 120.9）和顯著的生物降解作用，因此它具有第二高的去除效率。 此外，為了瞭解木屑系統的穩定性及再現性，我們在不同條件下進行管柱實驗;分別改變了初始濃度、操作時間、流速及季節、地區、木屑種類。以上操作條件皆不會影響木屑系統對於目標化合物的去除，然而硝酸鹽去除效果則會受到流速提升而明顯降低。由於木屑系統主要以脫硝為主要目的，因此在設計參數時要以脫硝效果為優先考量。 總體結果表明，木屑反應系統是一個很好的屏障，可降低地表及地下水受新興污染物污染的風險，並且擁有良好的穩定性以及再現性。

The woodchip bioreactor is a natural and inexpensive solution to nutrient pollution, which has become a growing concern in recent years. However, in addition to nutrients, emerging contaminants have also been detected. This study investigates the fate of eight commonly detected emerging contaminants though the woodchip bioreactor. The removal efficiency of the eight compounds in the woodchip system is heavily compound dependent: acetaminophen (ACE, completely removed), caffeine (CAFF, 60-80%), sulfathiazole (SFZ, 60-80％), 5-methyl-1-H-benzotriazole (TT, 55-80％), benzotriazole (BT, 35-80％), carbamazepine (CBZ, 40-60％), lincomycin (LIN, < 30％), and ibuprofen (IBU, <10％). Biodegradation is the dominant degradation mechanism for ACE removal, while sorption is the main mechanism for removing SFZ, TT, BT and CBZ (Kd = 145.2, 35.5, 35.6, and 36.6, respectively) through the woodchip bioreactor. Compounds in anionic forms (such as IBU) are least likely to be adsorbed, while the sorbability of compounds in their nonpolar, neutral forms (CAFF, ACE, CBZ, TT, BT, and LIN) increases with their KOC values. However, when all eight target compounds are present in artificial stormwater, competitive adsorption is observed, and all target compound Kd values decrease. Because CAFF undergoes both sorption (Kd = 120.9) and biodegradation in the woodchip bioreactor, it has the second highest removal efficiency. The woodchip bioreactor is very stable because the removal of the target compounds is unaffected by compound initial concentrations (100 and 1000 μg/L), flow rates (1 and 5 mL/min), or operation times (15 to 40 days or more). Furthermore, changes in season (June to February), region (California and Taipei), and woodchip source (American and Taiwanese) have no effect on removal efficiencies, demonstrating the system’s performance reproducibility. The overall results suggest that the woodchip bioreactor is an effective method to reduce the risks of emerging contaminants.