Characteristics And Mechanism Of Tetracycline,Cd²⁺ Adsorption By Modified Rice Straw

With the rapid development of modem industry and economy,a large amount of municipal solid waste,pesticide,chemical fertilizer and industrial sewage into water body,this had contributed to serious problem of water pollution in China.The pollution of tetracycline and heavy metal cadmium had became a hot issue of the public.Aiming at the reuse of discarded rice straw and its treatment of tetracycline hydrochloride(TCC-HCl)and Cd2+ pollution in wastewater,rice straw was modified with KMnO4,KOH,H2O2,KOH+H2O2,tartaric acid,citric acid,and TiO2,marked separately as RS/KMnO4?RS/KOH?RS/H2O2?RS/KOH+H2O2?RS/C4H6O6?RS/C6H8O7 RS/TiO2.These adsorbents were analyzed by scanning electron microscope(SEM),X-ray diffraction(XRD),FTIR spectrometer,specific surface area and aperture analyzer,and Zeta potentiometer.Comparison the differences in adsorption properties of TCC-HCl and Cd2+ by 7 modified rice straws in the same test system.Modified rice straw with good adsorption and friendly environment was selected(RS/KOH).The effects of various factors including adsorbent dosages,pH values of the wastewater,contaminant initial concentrations and the ambient temperatures on the adsorption process were investigated and analyzed.Adsorption kinetics and adsorption isotherms were analyzed.The adsorption mechanism of modified rice straw was preliminarily discussed.The main experimental process and results of the study in this paper:(1)The characterization results showed that apparent changes in surface morphol-ogy of RS/KMnO4,a lot of pores and channels were added to the surface.The surface area and pore volume of RS/KOH?RS/KOH+H2O2?RS/KMnO4 had increased in varying degrees.RS/KMnO4 cellulose,lignin and hemicellulose had different degrees of damage.RS/KOH+H2O2 lignin and hemicellulose had different degrees of damage.The surface of RS/CK is smooth with a tight cellulose structure.It was known from the change of Zeta potential,when the pH value was 7,RS/KMnO4 zeta potential was the lowest,it showed the most negative charges on its surface with the strongest electrostatic adsorption.(2)Comparison the differences in adsorption properties of TCC-HCl by 7 modified rice straws in the same test system,rice straw modified with KMnO4 had the best TCC-HCl adsorption in the aqueous solution,and the adsorption capacity was 9.48mg/g TCC-HCl,it's 4.86 times of the unmodified rice straw.Followed by RS/KOH and RS/KOH+H2O2.The adsorption order of modified rice straw treatments was:RS/KMnO4>RS/KOH>RS/KOH+H2O2>RS/C4H6O6>RS/C6HSO7>RS/H2O2>RS/TiO2>RS/CK.It was found that apseudo-second order kinetic model was the proper approach for describing the whole process of adsorption.Sum up,the rice straw modified by KMnO4,KOH and KOH+H2O2 could be the potentially valuable adsorbents for absorbing TCC-HCl in the wastewater solution.(3)Comparison the differences in adsorption properties of Cd2+ by 7 modified rice straws in the same test system,rice straw modified with KMnO4 had the best Cd2+adsorption in the aqueous solution,and the adsorption capacity was 10.024mg/g Cd2+,it had an increase of 99.44%compared with unmodified rice straw.Followed by rice RS/KOH and RS/KOH+H2O2.Compared with unmodified rice straw treatment,Cd2+removal of rice straw modified with KOH and KOH+H2O2 had increases of by 85.07%and 82.83%,respectively.The adsorption order of modified rice straw treatments was:KMnO>KOH>KOH+H2O2>TiO2>H2O2>RS/C6H8O7>RS/C4H6O6.It was found that quasi first order rate equation only described the initial stage of Cd2+ adsorption suitably,however,pseudo-first-order,modified pseudo-first-order kinetic model was the proper approach for describing the whole process of adsorption.Sum up,the rice straw modified by KMnO4,KOH and KOH+H2O2 could be the potentially valuable adsorbents for absorbing Cd2+ in the wastewater solution.(4)Modified rice straw with good adsorption and friendly environment was selected(RS/KOH)to test its adsorption characteristics.They showed different effects on the absorption process indicated by that the sorption capacity is strongly dependent on the initial pH values of the solution,whereas weakly depends on the RS/KOH dosage,initial TCC-HCl concentration and the ambient temperature.the pseudo-second-order kinetic Iodel gave the better correlation with the index R2 of 0.998-1,indicating that the model could appropriately describes the absorption process.The maximum adsorption capacity of RS/KOH for TCC/HCl obtained from the fitting has a value of 61.26 mg/g.(5)Modified rice straw with good adsorption and friendly environment was selected(RS/KOH)to test its adsorption characteristics.They showed different effects on the absorption process indicated by that the sorption capacity is strongly dependent on the initial pH values of the solution,whereas weakly depends on the RS/KOH dosage,initial Cd2+ concentration and the ambient temperature.The pseudo-second-order kinetic model could appropriately describes the absorption process.The maximum adsorption capacity of RS/KOH for TCC/HCl obtained from the fitting has a value of 13.677 mg/g.(6)The microbial communities and function relationship in experimental group and control group were analyzed through Illumina high throughput sequencing technology.Among them,the bacteria diversity in the E1 analogue column was the largest,and the bacteria abundance in the E2 analogue column was the largest.The proportion of biodegradation of antibiotics and nitrogen bacteria in the experimental group was higher than that in the control group.The experimental group had an obvious removal effect on NO3--N,for TCC-HCl and PO43--P,the experimental group had a certain removal effect,for NH4+-N,there is no obvious removal effect.The control group had no obvious removal effect on the above substances.