Degradation Of Roxarsone By Biochar-Mediated Shewanella Oneidensis MR-1

As a substance often used to promote the growth of livestock and other animals and improve the pigmentation of meat,roxarsone can be converted into intermediate products such ’as inorganic arsenic in the environment,causing pollution to the environment.Shewanella oneidensis MR-1(MR-1)is a metal-reducing bacteria that can use lactic acid as its electron donor under anaerobic conditions to reduce roxarsone and other substances.Biochar is a stable carbon-rich solid produced by the thermal decomposition of biomass.This thesis takes roxarsone as the target pollutant,and explores the effect of biochar on the degradation of roxarsone by MR-1.The main research results are as follows:(1)When the concentration of roxarsone is constant,the addition of biochar can significantly increase the degradation rate(%)and removal rate(mmol/L/h)of roxarsone.With the change of the amount of biochar added,the order of removal rate from large to small is:0.5 g/L biochar group>0.1 g/L biochar group>1.0 g/L biochar group>0.05 g/L biochar group.From the changes in the content of extracellular polymer secreted by MR1 and the results of scanning electron microscopy,biochar can’t cause physical damage to the surface of MR-1,and it can promote the growth of MR-1 and the degradation of roxarsone by MR-1.(2)With the increase of biochar pyrolysis temperature,the degradation rate and removal rate of roxarsone can be obviously increased.The removal rate increases with the increase of biochar pyrolysis temperature:BC600 biochar group>BC500 biochar group>BC300 biochar group.From the characterization of biochar,as the pyrolysis temperature increases,the total specific surface area,micropore surface area,and micropore volume of biochar generally increase,and the average pore diameter decreases.Through infrared spectroscopy analysis,it can be known that as the pyrolysis temperature increases,the degree of condensation of biochar increases,thereby increasing the pollutant removal rate.From the relative concentration of MR-1 and its secreted extracellular polymer content changes and the results of confocal microscopy,as the pyrolysis temperature increases,the growth promotion ability of biochar also increases.(3)There is a non-linear relationship between the initial concentration of roxarsone and the degradation rate and removal rate of roxarsone by MR-1 combined with biochar.When the initial concentration of roxarsone was 0.2 mmol/L,the removal rate was the largest.At the same time,as the relative concentration of MR-1 increased,the difference in the removal rate and degradation rate of roxarsone was smaller compared with the biochar combined MR-1 group compared with the MR-1 group alone.(4)The higher the initial concentration of roxarsone,the higher the relative concentration of MR-1,and the lower the content of extracellular polymer secreted by MR-1.In the presence of biochar,the relative concentration of MR-1 was lower,and the difference in the content of extracellular polymer secreted by MR-1 was greater.