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Using cathode of dual-chamber microbial fuel cell to treat high concentrations of cardiovascular drugs and antibiotics wastewater
Wastewater Treatment,Microbial Fuel Cells,Metoprolol,Electro-Fenton Reaction,Tetracycline,Alkaline Thermal Hydrolysis,
|Publication Year :||2021|
電Fenton實驗，於陽極使用含磷酸鹽緩衝溶液的模擬污水並以葡萄糖混合溶液作為碳源，在陰極則以pH調整至3之Na2SO4作為電解質，本研究測試了低比表面積的板狀材料石墨棒與鋼板、高比表面積的活性碳塗佈電極與奈米碳管塗佈電極、具有催化性的TiO2電極、以及同時具有高比表面積與催化性的氧化錳碳氣凝膠電極，研究發現催化性材料與其他材料，具有不同的反應趨勢，且同時具有催化性與高比表面積的氧化錳碳氣凝膠，其雙氧水產率達到石墨棒的15倍以上。以碳氣凝膠電極，進行以微生物燃料電池驅動的電Fenton反應，可在120 min內將125 mg L-1之美托洛爾去除60%以上。
鹼性環境加熱水解實驗，則在陰極加入100 mg L-1之四環素，並測試石墨與碳氣凝膠電極在開路、閉路或無電極狀態之下，於25、35、45、55 ℃，對四環素的去除效能。因為pH值的上升，所有閉路槽之四環素降解速率都優於開路槽。且溫度增加會使四環素的半衰期大幅縮短。TOC的分析則發現，不論開路或閉路槽都並未發生顯著的TOC去除，暗示四環素被轉化成二次產物。高解析度質譜儀指出，透過鹼熱水解反應，四環素的官能基群已經發生變化，可能會導致其抗菌毒性降低。而透過微生物毒性測試的驗證，經過陰極槽反應的四環素抗菌活性已經降低。研究結果顯示透過微生物燃料電池驅動鹼熱水解反應，可以有效的對含高濃度四環素的污水進行預處理，降低其抗菌活性，減少後續生物處理中，抗藥性基因出現的風險。
The application of microbial fuel cells (MFCs) on wastewater treatment has been evolving rapidly in recent years. It simultaneous removes pollutants and recovery energry in duving wastewater treatment process. There were many different MFC designs. In addition to single-chamber and micro chamber MFC capable of generating high power density, dual-chamber MFCs, which carry out reactions seprtatedly in indinduel chambers can produce valuable byproducts on the cathode. In the dual-chamber MFC, the microorganisms grow in the anode chamber and valuable byproducts such as H2, CH4 and H2O2 were generated in the cathode chamber depending on different design and external resistance. By reducing the external resistance of MFCs, the generation of H2O2 at the cathode could reach a concentration level to drive the Fenton reaction, which provides a strong oxidant to degrade pollutants. The rising pH in the cathode chamber can also drive alkaline thermal hydrolysis reaction, to degrade pollutants which are unstable characteristics under alkaline conditions such as tetracycline. These treatment procedures have potential to cope with several challenges faced by biological treatment in recent years: energy recovery, recalcitrant substances, and the spread of drug-resistant genes.
This research has two objects; in the object 1 I tested the hydrogen peroxide yield of various electrode materials, and used them to drive the electro-Fenton reaction to degrade refractory pollutants, such as metoprolol. In the object 2, the experiment focused on the utilization of alkali. In the process of generating hydrogen peroxide, a large amount of hydrogen ions from the cathode will be consumed, resulting in a significant pH increase, which may inhibit the Fenton reaction. However, this pH increase can be used to achieve degradation of unstable pollutants under the alkaline condition, such as tetracycline.
In object 1, a glucose medium containing phosphate buffer solution was used as an anolyte, and Na2SO4 solution with pH adjusted to 3±0.1 was as a catholyte. Cathode materials were selected according to previous electro-Fenton systems, such as non-catalytic materials such as steel plate and graphite, high specific surface area materials such as activated carbon and carbon nanotubes, catalytic materials such as platinum titanium, and high specific surface area catalytic materials such as manganese oxide/carbon aerogel. Our research have found that catalytic materials and other materials had different reaction trends, and manganese oxide carbon aerogel with catalytic properties and high specific surface area, achieved the H2O2 production rate is more than 15 times that of graphite rods. Using carbon aerogel electrode to carry out electro-Fenton reaction, 125 mg L-1 of metoprolol can be removed by more than 60% in 120 mins.
In the object 2, to test the degradation of tetracycline under different reaction conditions, including no-electrodes, carbon-aerogel-open-circuit, graphite-open-circuit, carbon-aerogel-closed-circuit, and graphite-closed -circuit, condictions 100 mg L-1 tetracycline was added, and the temperature was set to 25, 35, 45and 55 ℃, respectively. It was observed that tetracycline degradation rates under closed circuit conditions were faster than those under open circuit conditions due to the rising pH in the cathode chamber of closed circuit MFCs, and the temperature increase could result in a decrease in half-life of tetracycline degradation. The TOC analysis showed that most TOC was not removed after 48 h reaction, suggesting tetracycline was mainly transformed to byproducts in the cathode chamber. High resolution mass spectrometry identified the transformation products resulting from the alkaline thermal hydrolysis of tetracycline, and the minimum pharmacophore of tetracycline was altered, which would lead to the loss of antibacterial activity. Microtox tests confirmed the reduction in the toxic effect of tetracycline to luminescent bacteria after treatment in the cathode chamber. Our results have demonstrated the effective degradation of tetracycline using MFC-driven alkaline thermal hydrolysis, which will have potential to be a pretreatment process to assist the subsequent biological treatment processes to destroy high concentrations of antibiotics in the wastewater.
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