Long term effects of tetracycline on biological nitrification and denitrification

The influences of tetracycline (TET) in performances of biological nitrogen removal were investigated in this study. First stage of the study involved the dosing of 50 ppb, 20 ppb and 0 ppb of TET in three different sequencing batch reactors followed by 5ppm, 2ppm and 5ppm of dosage in 1#, 2# and 3# reactor respectively. This study emphasized on the efficiency of nitrification and denitrification process by analyzing the removal efficiencies of total nitrogen, ammonium and nitrate. Specific oxygen utilization rates (SOUR)s of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were also measured for further investigation in the microbial community. Results showed that trace TET dosage did not induce significant effects in the nitrification and denitrification process as the total nitrogen, ammonium and nitrate removal efficiency were almost unaffected. With the prolonged exposure of trace level of TET, the subsequent TET dosing of 2ppm and 5ppm showed little fluctuations in the beginning but the overall removal efficiency of total nitrogen, ammonium and nitrate soon recovered to initial standard. This showed that with a pre-dosing of TET, the microbial community in the reactors was capable of adapting faster and better in the following dosing of high concentration TET. Without prior exposure to TET, the sudden dosing of 5ppm affected the removal mechanisms in 3# reactor and decreased the average removal efficiency of total nitrogen and nitrate by 3% and 3.91% respectively as compared to no TET dosage condition. Incomplete ammonium removal was observed in some sets of data during phase 2 in 3# reactor which indicated that the activity of AOBs was impacted. Based on the decreasing (SOUR)NO2 in phase 2 of 3# reactor, it was determined that the activity of nitrite oxidizing bacteria (NOB) was also inhibited due to the sudden dosing of 5ppm TET and accumulation of nitrite was observed across several days during phase 2. These thus reduced the nitrification efficiency.Bachelor of Engineering (Environmental Engineering