It was notable that antibiotic concentrations in feed increased overall due to the continuously decreasing feed volume over time. However, a decreasing trend was observed at early stage. It was believed that this phenomenon was not derived from the penetration of antibiotics through the membrane since antibiotics in permeate were detected at very low concentrations. Adsorption of antibiotics onto membrane was speculated to be the reason as fluoroquinolones and macrolides exhibit high sorption property due to their high solid-water partition coefficients (Kd) [13].
Results of membrane extraction experiments confirmed the adsorption of antibiotics onto membrane. Adsorption amounts of AZI or ROX were higher than those of NOR or OFL (see Table 3). This could be attributed to different properties of the antibiotics and the specific characteristic of NF membrane. Under the experimental conditions, NOR and OFL were present in neutral forms, while AZI and ROX were positively charged, according to their pKa values. Polyamine membrane was usually negatively charged in solution at pH 7 [14] and [29]. Therefore, electrostatic interaction between the positively charged species and the negatively charged membrane could enhance the adsorption of AZI and ROX onto membrane. An overall mass balance calculation was carried out to estimate the adsorption amounts of antibiotics onto membrane as well (see Table 3). Nevertheless, the calculated results did not agree well with the results of direct extraction measurement. The reason could be the inadequate desorption of the antibiotics from membrane in extraction experiments, or their adsorption onto other components of the NF system. The same situation was reported in previous study [30].
โดดเด่นที่ความเข้มข้นของยาปฏิชีวนะในอาหารเพิ่มขึ้นโดยรวมเนื่องจากปริมาณอาหารลดลงอย่างต่อเนื่องช่วงเวลาได้ อย่างไรก็ตาม มีแนวโน้มลดลงถูกสังเกตในระยะแรก ๆ มันเป็นความเชื่อว่า ปรากฏการณ์นี้ถูกไม่มาเจาะของยาปฏิชีวนะผ่านเมมเบรนเนื่องจากยาปฏิชีวนะใน permeate พบที่ความเข้มข้นต่ำมาก ดูดซับของยาปฏิชีวนะเข้าสู่เมมเบรนถูกคาดให้ เหตุผลเป็น fluoroquinolones และ macrolides แสดงคุณสมบัติดูดสูงเนื่องจากสัมประสิทธิ์ของพาร์ติชันทึบน้ำสูง (Kd) [13]Results of membrane extraction experiments confirmed the adsorption of antibiotics onto membrane. Adsorption amounts of AZI or ROX were higher than those of NOR or OFL (see Table 3). This could be attributed to different properties of the antibiotics and the specific characteristic of NF membrane. Under the experimental conditions, NOR and OFL were present in neutral forms, while AZI and ROX were positively charged, according to their pKa values. Polyamine membrane was usually negatively charged in solution at pH 7 [14] and [29]. Therefore, electrostatic interaction between the positively charged species and the negatively charged membrane could enhance the adsorption of AZI and ROX onto membrane. An overall mass balance calculation was carried out to estimate the adsorption amounts of antibiotics onto membrane as well (see Table 3). Nevertheless, the calculated results did not agree well with the results of direct extraction measurement. The reason could be the inadequate desorption of the antibiotics from membrane in extraction experiments, or their adsorption onto other components of the NF system. The same situation was reported in previous study [30].
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