Enhanced Treatment Of Sulfide-containing Dyeing Wastewater By Biochar

China is the world’s largest producer of dyes,the use of dyes and emissions is huge,in different types of dyes,azo dyes are the most widely used dyes.Due to the dyestuff is difficult to be degraded under natural conditions,it is toxic and does great harm to human health and ecological environment.Sulphur is widely distributed.In the absence of oxygen,low-price sulfide will exist in large quantities in the environment in the form of ions(S^2-)or gases（H₂S）,which will give off a foul odor and make people or animals toxic.Sulfur compounds are often found in dye wastewater,which will reduce azo dyes slowly under suitable conditions and reduce the adverse effects of the two pollutants on the environment.In recent years,carbon materials have been used more and more in the environment,among which biochar materials have been widely used in the adsorption and catalytic degradation of dyes,sulfides and other pollutants due to its rich surface functional groups and large specific surface area.Therefore,the simultaneous treatment of dyes and sulfides with biochar may be a feasible,effective and novel solution.The purpose of this study is to use low-cost and environmentally friendly biochar materials,such as corn stalk（CSB800）,rice stalk（RCB800）,soybean stalk（BSB800）and other agricultural wastes from a wide range of sources,to promote the reduction of azo dyes by sulfur compounds.The relationship between the characterization characteristics and catalytic effect of different biomass carbon materials was discussed.By investigating the catalytic effect of electron mediator and the reduction effect of polysulfides,the positive effects of oxygen-containing groups and active polysulfides in the degradation process were discussed.The main conclusions of this paper are as follows:（1）The results of elemental analysis showed that carbon,hydrogen,oxygen and nitrogen were the main components of biochar materials.The hydrogen to carbon ratios of RCB800,BSB800 and CSB800 were 0.22,0.29 and 0.28,respectively.The results of TEM and SEM showed that the massive structure,rough surface and mesoporous structure of the biochar material were observed at the nanometer and micron scale.The results of energy dispersion spectrum showed that the biochar material contains some ash and sulfide would bind to the surface of the material.X-ray diffraction analysis results showed that the biochar material had graphitized structure.X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FTIR）analysis showed that the surface of biochar material contained abundant oxygen-containing functional groups,including quinone and carboxyl groups.Nitrogen adsorption and desorption test results showed that the materials contain mesoporous structures.The specific surface areas of the three biochar materials RCB800,BSB800 and CSB800 were 246 m²/g,210 m²/g and 225 m²/g,respectively.（2）The reduction of azo dyes by sulfides could be accelerated with the help of three biochar materials.The biochar material RCB800 prepared from rice husk had the most outstanding effect.It started to degrade rapidly in 14 minutes.The degradation rate of azo dye was 96.6%in 40 minutes,and the efficiency was 100%in 50 minutes.This series of biochar materials could adapt to a wide range of temperature（20℃to40℃）and p H value（6.2-8.1）,among which the optimal p H was 7.4 and the optimal temperature was 40℃.The concentration of methyl orange had little effect on the degradation efficiency per unit concentration,while the concentration of sulfide had a great effect on the reduction process.The best degradation effect was achieved when the concentration of sulfide was 8m M.Biochar had a good catalytic reduction effect on methyl orange and methyl red.The methyl red could be degraded rapidly in about7 minutes,and the degradation could be completed in about 20 minutes.（3）The degradation effect of biochar material RCB800 was similar to that of commercial carbon material carbon nanotubes;The RCB800 material used for the third time could also have a good degradation effect,the efficiency was only decreased by about 14%;The rate of polysulfide reduction of azo dyes was very high,only about 2 minutes to begin rapid decomposition,degradation was completed in 5minutes;Electron-mediator anthraquinone 2,6-disulfonate AQDS containing quinone structure,500mg/L AQDS could completely degrade the dye in 40 years;The mesoporous zeolite ZSM-5 had similar catalytic degradation performance to RCB800.（4）The Gompertz model was used to calculate the reaction kinetics in the experiment,and the fitting effect was good,and the correlation coefficients were all greater than 99%.Combined with the results of characterization and batch experiments,the ratio of hydrogen to carbon,oxygen-containing functional groups,specific surface area and mesoporous structure of the materials had a positive effect on the catalytic degradation performance.Sulfides had a greater impact on the degradation process and active polysulfides played an important role in the degradation reaction.In this study,the preparation of biochar materials showed excellent performance in the sulfide-mediated reduction of azo dyes,providing a new method to improve the degradation efficiency of azo dyes and sulfides by utilizing biochar materials from agricultural waste.