| As a kind of synthetic antibacterial drugs which is widely used, fluoroquinolones (FQs) antibiotics has been detected in the waters around the world. However, studies show that conventional water treatment process is not effective in removing trace amounts of antibiotics. These pollutants will eventually pose a serious threat to human health and the ecological environment through the migration and transformation in the environment, the enrichment of the food chain and the role of resistant bacteria. Therefore, it is necessary to seek an effective treatment to remove these antibiotics. Two kinds of FQs which has a higher frequency of detection (levofloxacin (LVF) and norfloxacin (NOR)) were selected. The removal efficiency, removal regularity and mechanism of action of the LVF and NOR in the process of biological activated carbon as well as the adsorption of activated carbon were studied. And the effect of FQs on microorganism in biological membrane was investigated.Activated carbon showed a high adsorption rate for FQs.250mL LVF and NOR solution of 20mg/L were adsorpted by 50mg four kinds of powdered activated carbon. The adsorption capacities of the four kinds of activated carbon are arranged as follows:qe(KOH modification)>qe(NHCl modification)>qe(F modification)>qe(A modification). The adsorption rate was large at the beginning, and then slowed down, almost reached a balance within 2 hours. The adsorption process follows the first order kinetics equation basically, and the correlation coefficient R2 are mostly above 0.96. Langmuir and Freundlich isotherm equation were used to fit the adsorption data,and the correlation coefficient R2 of Langmuir isotherm was found mostly above 0.96, which was higher than the R2 of Freundlich isotherm(<90%). Using 50 g/L KOH and NH4C1 solutions to modify activated carbon, the adsorption capacity and adsorption rate of the activated carbon increased with the rise of the surface and the free hydroxyl. At the same time, KOH modification was found to be slightly better than NH4Cl modification. When the temperature rises from 25℃ to 45 ℃, the saturation adsorption capacity of activated carbon is basically unchanged. In addition, the interaction between activated carbon and antibiotics LVF and NOR is mainly due to the hydrogen bond and acid-base interaction, and the main factors affecting the adsorption rate were the hydrophilicity and the pore size of the activated carbon.The removal rate of drinking water containing FQs antibiotic with 500 ug/L influent concentration by biological activated carbon column was at least 90%. The removal of NOR in the biological activated carbon column was compared with the early stage and the later stage of the drug administration. The removal of NOR in the early and late stage of drug administration in the biological activated carbon column was compared. During the initial stage of the operation, the concentration of antibiotics in the water decreased exponentially with the increase of altitude, in which the average concentration of effluent was 5ug/L and the removal effect was mainly caused by adsorption. However, in the late period of operation, the concentration of pollutants decreased with the decreasing of altitude, in which the average concentration of effluent was 40 ug/L and the removal mechanism was the synergistic effect of adsorption and biology. The effects of DOC concentration, residence time, and temperature on the operation of biological activated carbon in water were investigated and the results showed that DOC and NOR were negatively correlated. When the concentration of DOC in water increased from 5mg/L to 10mg/L and 15mg/L, the average NOR concentration of effluent increased from 5 g/L to 10 g/L and 30 g/L respectively. However, when the temperature rises from 15℃ to 20 ℃, the removal of organic matter and drug does not show a regular change. In addition, when the residence time of the column is changed to 13.1min and 5.0min, the average concentration of NOR in the effluent is 29 mu g/L and 87 mu g/L. When residence time is too short, the stability of the biological activated carbon column becomes worse, and the effluent concentration increases. By comparing the A column with wood charcoal as filler and the B column with coal based carbon as filler, it’s not hard to see that the performance of activated carbon filler is an important factor that affects the operation of the biological activated carbon column. The specific surface area and pore volume of the latter are nearly 2 times as much as the former. And the latter has a remarkable effect on the adsorption of organic matter and NOR in water. What’s more, through the study of the biological activated carbon which has been mature, we found that, in terms of wood charcoal, activated carbon with biofilm had a larger specific surface and porosity than non biological carbon, the direct opposite of coal char. The study of the mechanism of biological activated carbon column in removing NOR in water showed that the degradation of pollutants by biological activated carbon column was the result of a synergistic effect of adsorption and biodegradation. For different activated carbon, the effect of adsorption and biodegradation is different. When NOR was in the woody biomass, the biodegradation accounted for 50% of the total removal rate. Adsorption plays a major role on the removal of NOR in the coal, while microorganisms only playing a role in 10%～20%.The study of microorganism on the biological activated carbon showed that in the direction of water flow, the number of microorganisms decreased, but the difference between microbial species was not huge. In order to understand the effect of the antibiotic NOR in water on the microorganism in activated carbon column, two dominant strains were selected. And the species was determined as the brevundimonas and the stenotrophomonas maltophilia. Through resistance training in medicated medium of different concentration, the drug resistance enhanced obviously. The minimum inhibitory concentration of brevundimonas diminuta increased from 2mg/L to 5mg/L while stenotrophomonas maltophilia’ increased from 5mg/L to 10mg/L. Highly resistant strains were selected to research and test resistance genes. Genes associated with quinolone antibiotic resistance was not found in gyrA Subunit, parC Subunit and qnr plasmid. Therefore, the improvement of the resistance of the two strains is not due to resistance gene and there may be other mechanisms to increase its resistance to drug resistance. Culture of filial generation showed that the resistance began to decline after multiple generations of culture if resistant culture for bacteria was no longer conducted. |
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