Study On The Treatment Of Ciprofloxacin Wastewater By Iron-carbon Particle Enhanced Constructed Wetland Microbial Fuel Cell System

Fluoroquinolones are commonly used as veterinary medical antibiotics,accounting for 17%of global market sales,as their overuse has led to the spread of antibiotic resistance in microorganisms.Ciprofloxacin(Ciprofloxacin,CIP is a third generation of synthetic quinolone antibacterial drugs,which has broad spectrum antibacterial activity and good bactericidal effect.It has biological antibacterial activity against most microorganisms.As a new broad-spectrum antibacterial drug,ciprofloxacin has strong biological permeability,high blood concentration and low cytotoxicity,so it can be frequently detected in the natural environment of water induces changes in the microbial community in the water environment,which promotes the spread of antibiotic-resistant strains and creates biodiversity pressure,which leads to gene transfer.Excessive use of antibiotics will cause the survival pressure of the microorganisms in contact,thus promoting the occurrence of antibiotic resistance,which has formed a hazard to human safety.Three experimental devices were used in this study:constructed wetland（CW）,constructed wetland microbial fuel cell（EG）and constructed wetland microbial fuel cell（TPFC）with new iron-carbon filler.It has been operated for 70 days respectively.The purification of pollutants in wastewater is completed through oxidation of microorganisms,absorption of plant roots,adsorption of filled substrate and ion exchange of microbial membrane at electrode,etc.,which is used to treat ciprofloxacin pollutants in wastewater.The test objects included removal efficiency of water pollutants,electricity production,changes in microbial community structure and differences in the abundance of resistance gene qnrsThe results are as follows:（1）Electricity generation performanceThe average voltage of TPFC reaches 300.16±12.12 m V,which is significantly higher than that of EG（180.36±16.73 m V）（P<0.05）.From day 0 to day 15,the microorganisms have not adapted to CIP stress,and the microbial community is not stable enough,so the voltage fluctuates.After 20 days,the microbial community gradually becomes stable,and the voltage also begins to rise.After 60 days,due to the influence of temperature and light and other factors,as well as the aging of the microbial community,the voltage begins to fluctuate and decline.The polarization curve was obtained by changing the fixed resistance from large to small at the later stage of the experiment.Internal resistance is the most important factor affecting the device performance.The peak power density of EG group is 0.697 m W/m²,while that of TPFC group is 3.552 m W/m².The peak current density of EG group is 16.598 m A/m².TPFC is 37.439 m A/m2,the internal resistance of EG is 400Ω,and the internal resistance of TPFC is 166Ω.TPFC has an obvious advantage in overall performance（P<0.05）,so TPFC containing iron carbon filler has a good electrochemical performance.It is this that creates conditions for the high removal rate of pollutants.（2）Removal of pollutantsThree groups of devices through the removal of major water pollutants,in the twenty-fifth day to a stable period.During the stable period,the removal efficiency of TP from TPFC was calculated to be 97.1%±2.5%during the experiment.51.6%±4.8%in EG group;68.1%±2.9%in CW group.The CIP removal rates of TPFC and EG were 91.2%±3.4%and 82.1%±2.3%,respectively.CW had the lowest efficiency of 75.1%±5.6%.For removing TN,COD and NH₄⁺-N.The efficiency of TPFC was 61.3%±2.3%,87.1%±3.3%and 84.6%±2.5%,respectively.The efficiency of EG was 59.3%±2.1%,80.1%±4.3%and 84.2%±2.9%,respectively.TPFC significantly improved the removal efficiency of TP and CIP（P<0.05）.The removal rates of COD,NH₄⁺-N and TN also increased,but the difference was not significant.In a word,compared with CW and EG,the removal efficiency of water pollutants in TPFC is higher,and the removal rate fluctuates less.（3）Microbial community and functional microorganismsThe total phosphorus removal rate of TPFC（97.1%±2.5%）was significantly higher than that of EG（51.6%±4.8%）and CW（68.1%±2.9%）.The removal rate of ciprofloxacin was also significantly increased（TPFC:91.2%±3.4%,EG:82.1%±2.3%,CW:75.1%±5.6%）（P<0.05）.This may be due to the higher abundance of microorganisms such as Burkholderia,hydrophilia and Proteus.Hydrophilic bacteria have a significant advantage in TPFC（P<0.05）,which is related to its phosphorus removal ability and antibiotic resistance,which is also the microbial reason for the advantage of TPFC.After the addition of CIP,the presence of CIP has a selective effect on the microbial species of microbial anode,and the TPFC device has a favorable effect on the growth and propagation of microorganisms.The efficiency of TPFC and EG to remove CIP is more than 80%.The resulting low concentration of CIP has little effect on microbial growth and reproduction.（4）Study of ciprofloxacin resistance genesIn TPFC,microbial resistance to the antibiotic CIP increased significantly.The ciprofloxacin resistance genes of cathode was lower than that of anode（TPFC:7.74/μL,EG:5.52/μL,CW:2.65/μL）,which might be related to the higher bacterial abundance of anode.The main reaction utilized by iron-oxidizing bacteria involves the use of ferrous ions as electron donors.All these factors lead to a high copy number of CIP resistance genes in TPFC.Thus,efficient removal of the antibiotic CIP was observed.The experimental study has proved that all three units have the ability to treat CIP wastewater.The whole process is environmentally friendly,cost-effective,short cycle and does not require a large number of chemical inputs.In terms of water purification capacity,due to the participation of iron oxidation,the removal rate of all kinds of pollutants by TPFC is good,with high and stable removal rate.In terms of electricity generation,iron-carbon microelectrolysis can promote the flow of electrons inside the device and enhance the activity of electric-generating microorganisms,so as to better reduce the internal resistance of the device and increase the electricity generation of the device.The addition of TPFC could be a promising new technique for the removal of cyprofloxacin from industrial wastewater.