Preparation Of Saccharomyces Cerevisiae/Nano Fe₃O₄ Composites And Their Performance For Atrazine Removal

Since 1970s,Atrazine（AT）,a herbicide,has been widely used all over the world for its good herbicidal properties,and has made great contributions to increasing agricultural production and income.However,in the actual weeding process,only a small part of AT can be absorbed by weeds to achieve weeding effect,while the vast majority of AT is left in the atmosphere,soil and water environment.With the increasing use of AT year by year,the accumulation of AT in the environment is increasing.Under the natural effects of atmospheric deposition and soil leaching,AT is constantly detected in surface water,groundwater and even drinking water on which human beings depend.To make matters worse,AT,as a refractory organic matter,is difficult to degrade naturally,and has a great toxic effect on animals and plants in the natural environment.The risk of carcinogenic,teratogenic and mutagenic effects of long-term exposure to AT is significantly increased.In order to solve the damage of AT to the ecological environment and reduce the harm of AT to human life,it is very important to investigate the new materials and new processes of atrazine economically and effectively.Therefore,it has become a hot research topic at home and abroad to adopt an economical and reasonable treatment method to study the migration and transformation of AT in the process of treatment,and to put forward the technological parameters for the treatment of AT.According to the properties and characteristics of atrazine,combined with domestic and foreign research experience,nano-Fe₃O₄ and Saccharomyces cerevisiae were immobilized in this study.Saccharomyces cerevisiae/nano-Fe₃O₄ composites were prepared to treat atrazine-contaminated wastewater.The magnetic nano-Fe₃O₄modified by biochar was prepared by coprecipitation method.The magnetic nano-Fe₃O₄ particles were encapsulated in sodium alginate and polyvinyl alcohol matrix（SA-PVA）together with Saccharomyces cerevisiae to form spherical magnetic bio-nanocomposites.HR-TEM,XRD,EDS,FTIR and hysteresis loops were used to characterize the prepared Fe₃O₄ particles.Meanwhile,the prepared Saccharomyces cerevisiae/nano-Fe₃O₄ composites were analyzed by SEM.The results show that the prepared Fe₃O₄ particles are spherical-like structure with a particle size of 10-20 nm.Biochar is successfully loaded on Fe₃O₄ particles,which makes the surface of Fe₃O₄particles rich in C-O,C=O,C-OH functional groups.The saturation magnetization of Fe₃O₄ particles is as high as 45.93 emu/g,and there is no hysteresis,coercivity and residual magnetization.SEM spectra showed that Fe₃O₄ particles and Saccharomyces cerevisiae were successfully encapsulated in SA-PVA matrix.The magnetic Saccharomyces cerevisiae/nano-Fe₃O₄ composites had large internal space,and microorganisms grew well in atrazine wastewater.Saccharomyces cerevisiae/nano-Fe₃O₄ composites were used to treat atrazine pollution.The effects of environmental temperature,water pH,rotational speed and atrazine concentration on atrazine removal were studied.The effects of nitrogen source,carbon source and Fe³⁺on atrazine removal were also studied.In addition,the mechanisms of atrazine removal by the Saccharomyces cerevisiae/nano-Fe₃O₄composites were discussed and the degradation pathway of atrazine was proposed.The results showed that at 28^o C,pH 7.0 and 150 rpm,the removal rate of atrazine by Saccharomyces cerevisiae/nano-Fe₃O₄ composites at 2.0 mg/L was 100%,and that of atrazine at 50 mg/L was 95.53%.Atrazine removal in water mainly depends on the biodegradation of microorganisms.Atrazine is removed by microorganisms as a nitrogen source and the only carbon source.Additional carbon sources severely inhibit the degradation of Atrazine（the inhibition rate of Atrazine is 41.7%when 100mg/L carbon source is added,while the inhibition rate is as high as 91.5%when it is increased to 5 g/L）.Nitrite can slightly inhibit the degradation of Atrazine（When the concentration of NO₂^-was up to 100 mg/L,the inhibition rate was about 25.8%）.Adding appropriate amount of nitrate was beneficial to atrazine degradation.Atrazine was removed from wastewater by dechlorination,dealkylation,deamination,isomerization and ring opening mineralization under the action of Saccharomyces cerevisiae/nano-Fe₃O₄ composites.Therefore,Saccharomyces cerevisiae/nano-Fe₃O₄composites material have great potential for the treatment of atrazine wastewater,and it is a green,economical and efficient treatment method.