| The salicylic acid production wastewater which comes from a chemical company in Jiangsu Province is a typical acidic saliferous phenolic toxic organic industrial wastewater. Its pH value is2, salt content is as high as2.5%and with high phenols, but the B/C is only0.07, so the conventional biological treatment is not suitable for this wastewater. Besides, the cost of physical method is very high, we choose Fenton method which is a kind of chemical oxidation method to treat this wastewater. In view the problem of large amount of sludge production of the traditional Fenton method, this topic put forward a Fe3O4-H2O2Fenton-like system based on a new type of magnetic nanosopic catalyst by Fe3O4nanoparticles preparation and surface modification. This study optimized the process operation parameters by means of discussing the salicylic acid production wastewater efficiency by this Fenton-like system, and proposed a feasible method for the wastewater.First of all, Fe3O4magnetic nanoparticles were prepared using chemical co-precipitation, and the surface was modified with tetramethyl ammonium hydroxide (TMAH) and meso-2,3-dimercaptosuccinic acid (DMSA), synthesizing five kinds of catalysts, which were named1#Fe3O4,2#Fe3O4-TMAH(1mL),3#Fe3O4-TMAH(2mL),4#Fe3O4-DMSA and5#Fe3O4-TMAH-DMSA respectively. The results showed that the mean size of the Fe3O4nanoparticles was around30nm and they showed a good disparity between20and80nm. The Fe3O4nanoparticles were coated by methyl, sulfydryl and carboxyl after surface modification, which leaded to better dispersing performance of the nanoparticles.Secondly, the catalyzed degradation of phenol by Fe3O4-H2O2Fenton-like system was investigated in this study. Under the condition of12±2℃,0.8mmol/L catalyst dosage,2.0mmol/L H2O2dosage, pH4.5and the reaction time of180minutes, the highest COD removal efficiency was72%, the removal rate of volatile phenol was close to100%.3#and5#catalysts revealed optimal reuse efficiency,1#was the worst. This Fenton-like system had an advantage in the amount of iron sludge producing compared with traditional Fenton method. The magnetic catalyst was able to realize quick separation and recycling under the action of outside magnetic field, and the catalysts can be reused.Finally, the treatment efficiency of salicylic acid production wastewater by Fe3O4-H2O2Fenton-like system was investigated in this study, and the process operation parameters were optimized. Under the condition of15±2℃,2.0mmol/L catalyst dosage,7.0mmol/L H2O2dosage, pH5.0and the reaction time of120minutes, salicylic acid production wastewater treatment got the best results that effluent COD value was between34and42mg/L, volatile phenol value was between0.21and0.43mg/L, the catalytic effect of3#and5#were best,2#and1#followed by,4#was the worst relatively. The stability of the nano Fe3O4catalysts can be improved by surface modification using TMAH and DMSA,5#catalyst was considered the optimal. Under the condition of20±2℃, pH5.0, residence time60min,7.0mmol/L H2O2dosage mixed in the influent,5#catalyst1.0~2.0mmol/L, operatied the reactor continuously, the effluent COD value was between40to50mg/L, volatile phenol value fluctuated near0.2mg/L, the chroma was between2to4times, the effluent was able to meet the emissions standards steadily after adjusting the pH.The innovations of this thesis are the application of nano Fe3O4-H2O2Fenton-like system in actual industrial wastewater treatment and continuous operation of the reactor by catalyst recycling. This Fenton-like system has improved the insufficient of high iron sludge producing problem of traditional Fenton system. This study has proposed a feasible method for the salicylic acid production wastewater treatment, meanwhile, this study has provided theoretical basis and guidances for the practical industrial application of nano Fe3O4-H2O2Fenton-like system. |
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