Study On The Magnetic Modification Of Cotton Biochar And Its Enhancement To The Bacterial-algal Symbiosis Reactor Regards To The Treatment Of Antibiotics Containing Wastewater

The main purpose of this paper is to explore the application of agricultural waste biomass based on biochar materials in the field of resourcezation of wastewater.In this paper,cotton straw was taken as the object to study the preparation of magnetic biochar and its adsorption effect on lead ions.Furthermore,the magnetic biochar was coupled with the bacterial-algal bioreactor to explore the treatment efficiency and mechanism for moxifloxacin containing wastewater.The main research contents and results of this paper are as followed.1.Firstly,magnetic biochar was prepared based on cotton straw,and the physical and chemical properties of the magnetic cotton biochar（MCB）and cotton straw biochar（CB）were systematically characterized to explore the adsorption effect of MCB and CB on lead ions and analyze the adsorption mechanism of the two kinds of biochar on lead ions.According to the SEM results,the surface of MCB is rougher than that of CB,and it has more uneven and irregular pores.The BET results showed that the specific surface area of CB was 356.68 m²/g,while that of MCB was 613.69 m²/g,the specific surface area of MCB was significantly higher than that of CB due to magnetic modification,which could provide more adsorption sites.The adsorption-desorption isotherm of MCB and CB is a mixture of type I and type IV,and the pore structure is composed of mesoporous and microporous,which is more favorable for CB and MCB to adsorb molecules of different sizes in the solution.FTIR results show that there are metal hydroxyl groups in MCB,which can promote the adsorption of metal cation through ion exchange process.The single factor experiment showed that when the dosage was 0.05 g,the temperature was 25,the initial concentration of Pb²⁺was 100 mg/L,the solution p H was 5,and the equilibrium time of adsorption of Pb²⁺was 6 h,the optimal removal rate（99.01±1.21%）and adsorption capacity（91.94±1.15 mg/g）were obtained.The pseudo-second-order model had the highest fitting degree（R²>0.99）for the adsorption process,indicating that chemical adsorption was the dominant mechanism in the process of Pb²⁺adsorption by MCB;Langmuir adsorption isotherm model accurately described the process of Pb²⁺adsorption,and the maximum monolayer adsorption capacity（Q_m）of Pb²⁺for MCB and CB were 208.33 mg/g and 156.25 mg/g,respectively.The results of adsorption thermodynamic model show that relatively low temperature can promote the spontaneous adsorption reaction,which is beneficial to reduce the energy consumption in practical application.2.Based on the good adsorption performance of MCB,the research of MCB coupled with bacteria algae symbiotic reactor in the domestic wastewater containing moxifloxacin treatment and the resource recovery in the wastewater treatment process were performed.According to the pre-experiment,the optimal ratio of activated sludge and Chlorella was 1:5.The system performance was evaluated by COD,NH₄⁺-N,TP,TN,moxifloxacin removal rate,oil content,chlorophyll content and other indicators.The extracellular polymers（EPS）of the mixture and changes of microbial community at different concentrations of moxifloxacin were analyzed,to explore the response of bacteria algae symbionts to moxifloxacin.The results showed that the removal efficiency of COD and NH₄⁺-N in the experimental group and the control group were above 80%,while the removal rates of TP and TN were relatively low,and the removal rates of TP and TN were higher than 65%and 57%respectively.When the concentration of moxifloxacin was 0.1-0.3 mg/L,the removal rate of the control group was 80.33±2.11%,the experimental group could completely remove moxifloxacin;when the concentration of moxifloxacin increased to 1-6 mg/L,the removal rates of the experimental group and the control group were decreased,the removal rates were 67.46±1.14%and 41.73±1.21%,respectively.The results showed that the system could not only remove COD,TP,TN,NH₄⁺-N and other pollutants,but also promote the removal of moxifloxacin.The results of oil and chlorophyll-a content were correlated.The maximum oil content of experimental group is176.63 mg/L,and the peak value of chlorophyll-a content is 57.90 mg/L,both of them appeared on the 20th day of the experiment,and the peak time of the experimental group was 10 days earlier than that of the control group,indicating that MCB provides attachment sites for the growth of Chlorella,which can promote the growth and biomass accumulation of Chlorella;with the increase of moxifloxacin concentration,the protein release increased,the polysaccharide content decreased,and new organic substances such as fulvic acid appeared,he said Moxifloxacin is released under microbial stress.Under the pressure of moxifloxacin,the diversity and richness of microbial community were affected to a certain extent.With the increase of moxifloxacin concentration,the diversity and richness of microbial community showed a downward trend.At the genus level,the dominant bacteria species were different in different periods.When the concentration of moxifloxacin was 0.1 and 0.5 mg/L,Saccharimonadales was the dominant bacteria at the genus level,accounting for 37.7%.When the concentration of moxifloxacin was 1 mg/L,Comamonas was the dominant bacteria in the control group,accounting for 30.6%.When the concentration of moxifloxacin was 6 mg/L,Thermomonas was the dominant bacteria in the experimental group.In conclusion,magnetic cotton biochar has good adsorption performance in this study,and this idea provided a new way for the recycling and efficient use of agricultural waste.Based on the MCB,further coupled with the bacteria algae symbiotic reactor,the performance of the system for the treatment of antibiotic containing wastewater was studied,and the results showed that the system was suitable for conventional wastewater treatment.The pollutants and moxifloxacin have high removal efficiency,and can produce oil through microalgae,effectively recover and utilize the bioenergy in wastewater,which provides new ideas and theoretical support for the engineering application of wastewater recycling.