Research On The Biological Ecological Treatment Of Ofloxacin Antibiotics In Sewage

Contamination of antibiotics in wastewater not only threatens the survival of aquatic animals and plants,but long-term exposure to antibiotics also increases the resistance of bacteria.Fluoroquinolones antibiotics are up to mg/L in wastewater from pharmaceutical factories and are also one of the currently used antibiotics.In this study,ofloxacin（OFL）in the fluoroquinolones was selected as the study object and the adsorption and biodegradation methods were used to remove it.In this study,the activated carbon（AC）perpared from loofah and activated by phosphoric acid was selected as the adsorbent.The characteristics of activated carbon,the effect of activated carbon dosage,initial concentration of ofloxacin,pH,temperature,and time on the adsorption effect,the mechanism of the adsorption and the optimum adsorption conditions were investigated.An activated sludge sequencing batch reactor（SBR）was fed with synthetic wastewater containing ofloxacin（OFL）for 52 days to study the effect of ofloxacin on the removal of chemical oxygen demand（COD）,ammonia nitrogen（NH₄⁺）and total phosphorus（TP）in wastewater,changes in the content and chemical compositions of extracellular polymers（EPS）and dynamic changes in microbial communities.（1）The activated carbon was characterized by using Scanning electron microscopy,Aperture analyzer and Fourier Transform Infrared Spectroscopy.It showed that the activated carbon had a rough surface with a well-developed porous structure.The AC surface area and the average pore diameter were 834.008 m²/g and5.35 nm,respectively.The phosphorus-containing functional groups,and C=O,C–O–C,and C=C bonds were formed on the AC surface.The effect of five single factors on the adsorption effect was studied.The results showed that with the increase of the amount of activated carbon,the removal rate showed an increased trend,and the adsorption capacity showed a downward trend.With the increase of the initial concentration of ofloxacin,the trend of removal rate and adsorption amount is opposite to that of activated carbon dosage.When the pH was 6,the highest removal rate and adsorption amount were achieved.With the increase of temperature,the removal rate and the adsorption amount showed a decreasing trend.The adsorption equilibrium was reached at a reaction time of 240 minute.（2）The pseudo-first-order kinetics,pseudo-second-order kinetics,and intraparticle adsorption models were used to fit the experimental data.It showed that the AC adsorption kinetic data were best described by the pseudo-second-order model（R²>0.998,?q was the minimal）;this shows that chemisorption control the adsorption.At 25,30,and 35°C,the Langmuir,Freundlich,Dubinin–Radushkevich,and Sips isotherm models were used to fit the experimental data.Compared with other models,the experimental data correlated well with the Freundlich isotherm model（R²>0.99）,indicating multilayer adsorption.From the data fitted by the Langmuir model,the maximum adsorption capacity of OFL was about 132 mg/g.The Gibbs free energy（ΔG）,enthalpy change（ΔH）and entropy change（ΔS）were calculated according to the data obtained from the adsorption isothermal experiments.TheΔG andΔH values were both negative;this shows the adsorption were spontaneous,exothermal.TheΔS values were negative,which showed that randomness decreased in OFL adsorption.Three factors and four levels of orthogonal experiments and analysis of variance were used to determine the optimal conditions for adsorption.It showed that the pH=6,initial OFL concentration=30 mg/L,temperature=298 K,and AC dosage=0.5 g/L were the optimum condition for OFL adsorption.（3）With the increase of ofloxacin concentration,the removal rates of COD and NH₄⁺are less affected by ofloxacin concentration,which is always higher than 85%and 96%.The removal rate of TP fluctuates greatly,showing an upward trend.It eventually stabilized at about 80%,and the removal rate of ofloxacin eventually stabilized at about 65%.The main components of the EPS are proteins and polysaccharides.The activated sludge sampleswere took from rector on first,25th and50th days to determine the content of protein and polysaccharide.The results showed that the concentration of the two increased with the concentration of ofloxacin.It indicated OFL promoted the EPS secretion to protect cells from OFL damage.The chemical compositions of EPS were determined by three-dimensional fluorescence spectroscopy（EEM）.The results showed that the chemical compositions of EPS increased the humic acid-like and fulvic acid-like organic substances from the 25th day to the 50th day.（4）Based on the data obtained from high-throughput sequencing,the dynamic changes of the microbial community were obtained.For denitrifying bacteria,the read number of Pseudomonas,Bacillus,Thauera,Comamonas,Azospira sharply decreased initially（p<0.05）and increased from Day 25 to Day 50.The read number of Paracoccus,Hyphomicrobiu,Novosphingobium displayed a decrease trend.The read number of Acidovorax decreased from Day 1 to Day 25 and sharply increased（p<0.05）,which against with the tendency of Rhodobacter,Flavobacterium.The read number of Rhodocyclaceae,a phosphorus-accumulating bacterium,increased,whereas the read number of Dechloromonas decreased.As for ammonia oxidizer,the read number of Nitrosomonadaceae significantly decreased from Day 1 to Day 25 and sharply increased（p<0.05）.The read numbers of NOB and anammox significantly declined under OFL pressure（p<0.05）.