Natural Materials Assisted Removal Of Micro-Pollutants Antibiotics In Water

Antibiotics,with the advantages of high efficiency,have been widely used to treat human and animal infectious diseases.Because of their poor metabolic capacity in humans and animals,and poor degradability in the environment,antibiotics with increasing concentration levels have been detected in the environment.Water environment is an important medium for antibiotic migration and transformation.It has been reported that up to date,different antibiotics have been detected in groundwater,lakes,reservoirs and seawater,which make aquatic organisms in the water produce resistance genes.Moreover,antibiotics will be harmful to human and animal body through food chain enrichment.Therefore,it is essential and urgent to remove antibiotics from the water.Among available methods,adsorption technology,as well as degradation technology,are popular in scientific research for a long time,and it is more meaning by combination of natural materials assisted removal of antibiotics.This is based on the following facts:(i)natural materials have many advantages such as abundant reserves,wide distribution,low price,biodegradability,good ecological compatibility,and so on,(ii)natural materials themselves can be used to remove pollutants in water or used as the template to fabricate adsorbent or degradable materials.Combined with the economic cost and performance advantages,natural materials can exert their potential values in practical applications.Therefore,the research on natural materials-based functional materials that are inexpensive,efficient,and practical is of great significance in water treatment.In this thesis,two natural materials are used to assist in the removal of antibiotics in water,and the research content includes two parts.With chitosan(CTS)as the graft skeleton,a granular hydrogel with a 3D network structure was fabricated and then used as the adsorbent to remove fluoroquinolone antibiotics.With tourmaline(TM)as the mineral catalyst and ammonium persulfate(APS)as the oxidant,a new TM-APS system was constructed for the degradation of sulfadiazine(SDZ)in water.Specifically,the research contents were summarized as follows:(1)A granular hydrogel(CTS-g-PAA)prepared from CTS as the grafted backbone and acrylic acid(AA)as the polymerizable monomer was used as the adsorbent to remove three typical fluoroquinolone antibiotics,i.e.ciprofloxacin(Cip),enrofloxacin(Enr)and levofloxacin(Lev).By investigating the effects of pH,contact time,adsorbate concentration,and ionic strength,as well as regeneration and reusability,the adsorption performance of CTS-g-PAA was systematically explored.The experimental results showed that CTS-g-PAA had a sponge-like 3D structure that was favorable for adsorption.CTS-g-PAA exhibited the best adsorption efficiency for three antibiotics at pH=3.0,with the maximum adsorption capacity of 229.7 mg/g for Cip and 339.6 mg/g for Enr,respectively.The adsorption of Cip and Enr was consistent with the monolayer Langmuir isotherm model,while the adsorption of Lev was more in line with the Freundlich isotherm model,rendering that Lev had not been reached the adsorption saturation over the concentration range studied(10~600 mg/L).The adsorption process of CTS-g-PAA for Cip,Enr and Lev occurred quickly,and could be well described by the pseudo-second order kinetic equations.The results of five consecutive adsorption-desorption experiments indicated that CTS-g-PAA had a good recycling performance.Moreover,CTS-g-PAA could effectively adsorb Cip in tap water,Yellow River water and domestic sewage,demonstrating that CTS-g-PAA had the potential for practical application in water treatment.(2)An advanced oxidation system using TM as the mineral catalyst and APS as the oxidant was constructed for the degradation of SDZ in water.Operating conditions were optimized by investigating the amount of TM,APS concentration,pH,SDZ concentration,and temperature.The reaction mechanism and degradation products were proposed and determined by combination of free radical quenching,electron spin resonance spectroscopy(EPR),total ion chromatograms(TIC)of liquid-mass spectrometry and absorbance degradation curves.The experimental results showed that the best degradation efficiency of TM-APS system on SDZ were obtained under the following conditions:TM amount,0.5 g/L;APS concentration,0.5 g/L;pH,3.0.The degradation efficiency increased when the temperature increased from 10~oC to 50~oC.In addition,inorganic anions in TM-APS system had a certain inhibition for degradation efficiency,while the presence of organic matter(such as humic acid in this study)showed a slight enhancement in degradation efficiency.According to free radical quenching and EPR experiments,?OH was the main free radical in TM-APS system,by which SDZ molecules were attacked to form new substances via desulfurization.Based on TIC results,the degradation mechanism of SDZ by TM-APS system was a heterogeneous Fenton-like reaction initiated by Fe active sites on TM surface.Taking account of the maximization of cost-effectiveness,TM could be utilized repeatedly and the fourth degradation efficiency was about 80%of the first time.Meanwhile,TM-APS system showed no significant differences on SDZ degradation in tap water and Yellow River water,indicating that the developed TM-APS system with the maximized economic benefits was feasible to apply in the actual water treatment process.