Study On Several Advanced Oxidation Techniques For Degradation Of Saccharine Sodium Wastewater

Saccharin sodium,namley O-benzoyl methyl sodium imide,is a representative of artificial sweeteners and has been widely used in the fields of medicine,beverages and daily chemicals.The production process of sodium consists of amidation,esterification,methyl ester blends,diazotization,substitution/chlorination,amination/secondary amination and alkalization,which makes the wastewater be shown with deep chroma,high salt and organic species contents,and poor biodegradability.In this thesis,the pretreatment process of Saccharin sodium wastewater was investigated.The contents include the analysis of the main pollutants in wastewater and the experimental studies on the treatment of saccharin sodium wastewater by using ozone oxidation,Fenton oxidation,ozone combined with Fenton oxidation and UV combined with Fenton oxidation respectively.（1）The analysis of the major pollutants in the wastewater.The physical property was evaluated by the national standard method.It showed that pH,turbidity,chromaticity,SS and conductivity was 11,32FTU,512 times,852 mg/L and 2.42 ms/cm,respectively.The contents of ammonia-nitrogen,total inorganic salts,sulfates,chloride ion and total copper in the wastewater were determined by Nessler’s reagent spectrophotometry,gravimetric analysis,barium-chromate spectrophotometric method,silver nitrate titration and ICP-AES,respectively.The sulfates and total copper were found to meet the emission standard,while the chroma and the contents of ammonia-nitrogen,total inorganic salt and chloride ion were higher than the emission standard.The levels of COD,BOD₅ and TOC indicated a large amount of organic matters in the wastewater,which was far exceeded the"Level III Comprehensive Wastewater Discharge Standard"（GB8978-1996）（BOD₅ 600 mg/L,COD 1000 mg/L）.（2）Ozone Oxidation.The degradation efficiency was affected by the dosage of ozone,reaction temperature and initial pH.The best parameters were the ozone dosage of 1.397×10^-2mol/s,initial pH of 11and the temperature of 308.15-318.15 K.Under such optimal conditions,the removal ratios of chroma,COD and TOC were achieved as 87.50%,60.47%and 43.09%respectively;and,the ratio of BOD₅/COD was increased from 0.24 to 0.32.（3）Fenton Oxidation.The dosage of H₂O₂ and Fe²⁺,initial pH and temperature played great roles that affected the degradation efficiency.The removal ratios of chroma,COD and TOC were achieved as74.97%,72.88%and 96.88%,under the optimal conditions of 80 mL/L H₂O₂,5-7 g/L Fe²⁺,308.15 K and pH 5.The ratio of BOD₅/COD was increased from 0.24 to 0.32.（4）Ozone combined with Fenton oxidation.Results showed the dosage of H₂O₂,Fe²⁺and ozone,initial pH and temperature have important effects on the degradation efficiency.The operation condition were 60 mL/L of H₂O₂ dosage,5 g/L of Fe²⁺dosage,1.397×10^-22 mol/s of ozone dosage,9 of pH and 308.15K of temperature.The removal ratios of chroma,COD and TOC were achieved as 84.29%,76.17%and98.44%.The BOD₅/COD was increased to 0.53 from 0.24,which improved the biodegradability.（5）UV combined with Fenton oxidation.Experiments based on single factor,including the concentration of H₂O₂ and FeSO₄,initial pH and reaction time were discussed and optimized by response surface method.The optimum conditions were determined as follows:120 min of reaction time,6 of initial pH,78 mL/L of H₂O₂ and 5 g/L of FeSO₄.The significance for each factor was in the order of H₂O₂dosage>initial pH>reaction time>FeSO₄ dosage.The interaction effect of the dosages of FeSO₄ and H₂O₂was remarkable.The linearly dependent coefficient for mathematical model was satisfied.The removal ratios of chroma,COD and TOC were achieved as 98%,89.75%and 89.14%under the optimum conditions.The BOD₅/COD ratio was increased from 0.24 to 0.64.