Study Of The Inhibition Of Fluoroquinolones On Anammox Bacterial Activity

Anammox (anaerobic ammonia oxidation) is a new type of biological nitrogen removal technology. Under anaerobic or anoxic conditions, anammox microorganisms directly use nitrite as an electron acceptor with ammonia as the electron donor, while the two nitrogen compounds come into nitrogen gas. The process has the advantages of not producing greenhouse gases, without aeration and without addition of carbon source. Using anammox technology with low energy cost treating actual wastewater has become a hot issue. However, due to extensive use of antibiotics, antibiotics can be found in pharmaceutical wastewater, medical wastewater, swine wastewater even in domestic sewage. As a result, the antibiotics in various kinds of wastewater are inevitable. Therefore, it is necessary to study the inhibition effect of antibiotics on anammox bacteria activity.The main research of this paper is to examine the inhibition effect on the anammox bacteria activity of actual wastewater with higher levels of fluoroquinolone antibiotics including levofloxacin and norfloxacin. To investigate the inhibition effects of these two antibiotics on the activity of anammox bacteria, short-term and long-term inhibition experiments have been conducted. The main findings are as follows:(1) In the short-term experiment, when concentration of norfloxacin increases to 200 mg/L, the total nitrogen removal rate decreases from 0.546 mg N/g VSS/h to 0.315 mg N/g VSS/h, which is 57.6% of the control. When concentration of levofloxacin increases to 400 mg/L, total nitrogen removal rate decreases from 0.762 mg N/g VSS/h to 0.4 mg N/g VSS/h, which is 52.5% of the control.(2) The half inhibition concentration of norfloxacin is 227.39 mg/L while the half inhibition concentration of levofloxacin is 386.75 mg/L. The inhibition effect of norfloxacin is stronger than levofloxacin.(3) In the long-term experiment, when the influent concentration of norfloxacin reaches to 10 μg/L, no significant inhibition effect has been found on anaerobic ammonia oxidation process. Nitrogen removal percentage and total nitrogen removal rate are 76.75% and 0.586 kg N/m3/d, while the control are 78.59% and 0.599 kg N/m3/d.(4) In the long-term experiment, with norfloxacin influent concentration increases from 25 to 50 mg/L, it will not produce significant inhibition effect on the anaerobic ammonia oxidation process. When norfloxacin concentration reaches to 75 mg/L, the anammox process is inhibited. Nitrogen removal percentage and total nitrogen removal rate decrease to 50.51% and 0.445 kg N/m3/d.(5) In the long-term experiment, when the influent concentration remains 150 mg/L, the anammox process is severely inhibited and collapsed after 36 d. Nitrogen removal percentage and total nitrogen removal rate decrease to 8.34% and 0.073 kg N/m3/d.