Mechanistic Study On The Removal Of Sulfachloropyridazine From Aqueous Solution By Long-root Eichhornia Crassipes Based Adsorbents And Persulfate

Sulfanilamides(SAs),as one of the cheapest and most effective veterinary drugs,were widely used in livestock and poultry industry.As they were discharged into environment by animal excreta and organic fertilizer,then accumulation took place.SAs were frequently detected in water environment and the detection concentration was up to ng/L～μg/L level.Long term exposure to SAs resulted in bacterial resistance,which seriously threatened ecological environment and human health.In this thesis,sulfachlorpyridazine(SCP)was selected as the target pollutant for its strong environmental migration ability.And Eichhornia Crassipes root was made into root powder,hydrochar and ethanol/water activated hydrochar to adsorb SCP from water.The effects of preparation parameters,adsorption parameters were compared to evaluate adsorption capacity(qe)of materials.The adsorption process was analyzed by various fitting models,and the functional groups on the surface of the materials were qualitatively and semi quantitatively analyzed by various characterization methods.In addition,thermal activated persulfate(PS)advanced oxidation technology was studied to degrade SCP in water,and the degradation parameters were optimized.The degradation mechanism was elucidated by the identification of oxidation free radicals and intermediate products.The main conclusions were as follows:(1)The root powder was fibrous with few surface pores and it could effectively adsorb SCP when pH value was less 4.At pH 2.0,the Lewis acid-base interaction and electrostatic attraction were strong and SCP removal reached top 53%.Higher SCP initial concentration was companied by higher qe but lower removal efficiency.The adsorption process followed pseudo-second order kinetic model(PSO,R2≥0.990),indicating that chemical adsorption was the key step.The intra-particle diffusion model(IPO)divided the adsorption process into three stages:boundary layer adsorption,internal diffusion and adsorption equilibrium.The higher the initial concentration of SCP was,the thicker the adsorbed boundary layer became.Langmuir and Freundlich models could well both fit the adsorption process(R2≥0.986),and the maximum qe was 226.76 μg/g(288.15 K).The adsorption process was a spontaneous exothermic reaction.Sulfonamides functional groups played a major role in the adsorption process,while heterocyclic groups played a secondary role.(2)At pH 5,SCP could be effectively adsorbed by acid modified materials,and qe was positively correlated with combined severity-CS(R2≥0.776),and the maximum qe was 702.03μg/g.With CS increasing,the carbonization degree,hydrophobicity,porosity and the zero electric point of hydrochar increased,but the content of polar functional groups decreased.When CS was more than 5.13,pseudo lignin spherical hydrochar was observed.With pH increasing,qe increased at first and then decreased.Hydrochar still worked at pH 7.The adsorption process was in accordance with linear PSO and Freundlich isotherm model,indicating the existence of chemisorption as multi-layer adsorption.The FT-IR wavenumber at 555.4 cm-1(porosity),2901.4/2919.2 cm-1(aliphatic CH),1374.51 cm-1(phenolic hydroxyl),3514.63 cm-1(carboxyl hydroxyl),1604.5 cm-1(aromatic skeleton)and 1227.47 cm-1(ester/phenol ether)were the key factors for qe.Multivariate linear equation between these six peak intensity and qe was established(R2 ≥0.933).In the pH range of 0.8～6.5,there was almost no electrostatic attraction between SCP and hydrochar.Under strong acid condition(pH<3),protonated amino groups in SCP+interacted with electron-rich functional groups(π electron,phenol ether and carboxyl group)on the surface of hydrochar by Hydrogen interaction.Under weak acid condition(3<pH<5),SCP0 acted as π electron donor to bond with hydrochar byπ-π electron donator-acceptor interaction.(3)After three times of ethanol/water activation,the hydrolysate on the surface of hydrochar was basically eluted,and the elution mainly contained C-O functional groups like alcohol/ether/carboxylic acid.With activation times increasing,qe,hydrophilicity and the content of polar functional groups of hydrochar increased,but the degree of carbonization decreased.The adsorption process obeyed linear PSO model.The activated hydrochar mainly had macropores,and the BET specific surface area ranged from 15.6 to 24.6 m2/g.The removal efficieny of SCP ranged from 51%to 93%at pH of 0.8 to 8.0.The qe of activated hydrochar was highest at pH=1.86,approaching 3149 μg/g.Activated hydrochar working in weak acid or weak alkali solution showed this material had a promising application prospect.(4)The degradation rate constant-kobs was quadratic with PS concentration(R2=0.923).And kobs decreased with pH rising.Higher activation temperature accelerated the decomposition of PS and SCP,but lowered the reaction stoichiometric coefficient.Thus 40℃ was selected as the optimal activation temperature.The presence of chloride(Cl-),bicarbonate(HCO3")and humic acid all showed inhibitory effects.The radical scavenging experiments revealed that SO4·-was predominant oxidizing species responsible for SCP removal.LC-MS/MS analysis confirmed seven kinds of byproducts during the removal process which were mainly deriving from SO2 extrusion/Smile-type rearrangement and S-N bond cleavage.There were mainly about 17 kinds of antibiotics in the piggery anaerobic fermentation slurry sample.Efficiencies of the antibiotics removal were over 85%when thermal activated PS technology was applied into degradation of piggery anaerobic fermentation slurry.