Experimental Study On Advanced Oxidation Process For Pretreatment Of Folic Acid Production Wastewater

Folic acid is one of the water-soluble vitamin B complexes.During the production of folic acid,a large amount of Refractory waste water will be generated,and its components are complex,mainly containing pteridine compounds,L-N-aminobenzoyl glutamic acid,2,4,5-triamino-6-hydroxypyrimidine sulfuric.It belongs to chemical industry wastewater with high organic matter concentration,high salinity and many refractory substances.The folic acid production process has been in China for nearly30 years,and the waste water problem has not been completely solved,which has become a bottleneck restricting of the development and application of folic acid production.In order to solve the problem of folic acid production waste water treatment,this paper used three advanced oxidation techniques,which are Fe/C microelectrolysis-Fenton method（Fe/C-Fenton）,diatomite supported Fe-Ni nanoparticles（NZVI/Ni/DM）and diatomite supported Fe-Ni nanoparticles-Fenton Method（NZVI/Ni/DM-Fenton）,for pretreatment of folic acid production waste water,with the removal rate of COD and NH₃-N as the inspection index.The effect of reaction conditions on the treatment of folic acid waste water were analyzed,such as the pH value,reaction time,dosage,et al,the degradation mechanism and degradation kinetics are discussed,which provides a theoretical basis for the actual industrial production needs.（1）Used iron scrap as zero-valent iron,adding activated carbon,amount of Fe²⁺will be generated in the reaction of the iron-carbon primary battery,and H₂O₂ will be added to form the Fenton reaction,thereby constructing the iron-carbon microelectrolysis-Fenton system.The effects of initial pH,iron-carbon ratio,iron-carbon dosage,reaction time,H₂O₂ dosage method,and H₂O₂ dosage on the treatment effect were studied during the treatment of waste water with iron-carbon microelectrolysis-Fenton technology.These results showed that the initial pH,iron-carbon ratio,reaction time and H₂O₂ dosage have a great influence on the treatment effect of folic acid production waste water.Under the optimal conditions of pH of 3,iron-carbon ratio of 2:1,hydrogen peroxide dosage of 800 mmol/L and reaction time of 120 min,the removal rates of COD and NH₃-N of folic acid production waste water can reach 36.87%and 77.68%,respectively.BOD₅/COD increased from 0.13 to 0.40.The reaction of iron-carbon microelectrolysis-Fenton reagent combined with pretreatment of folic acid production waste water conforms to quasi-second order dynamics.（2）Used diatomite as the carrier and nickel as the doped metal to support the nano-iron,prepare the diatomite supported Fe-Ni nanoparticles（NZVI/Ni/DM）composite material to improve the dispersion of the nanoparticles and enhance their reactivity.X-ray diffraction,scanning electron microscopy,specific surface area analysis,and X-ray photoelectron spectroscopy were used to characterize the iron-nickel loaded materials.Scanning electron microscopy found that most of the nano-iron-nickel was evenly loaded on the diatomite and dispersed evenly.A part of it was not loaded on diatomaceous earth and reunite.The loaded diatomaceous earth has a specific surface area of 37.74m²/g,a pore size of 10.20nm,and a pore volume of0.11cm³/g.XPS found that part of the loaded nano-iron nickel was oxidized.The effects of pH,reaction time,temperature,etc.on the progress of the treatment of folic acid production wastewater by NZVI/Ni/DM were investigated.The experimental results showed that at room temperature,the pH is controlled in the range of 1-3,the reaction time is 240 min,the shaker speed is 100r/min,and the amount of material added is 3g/L.The removal rate of COD can be up to 50%,and the removal rate of NH₃-N is 80%.BOD₅/COD increased from 0.13 to 0.42.The reaction of NZVI/Ni/DM in the treatment of folic acid production wastewater conforms to quasi-second order dynamics.（3）Combined the reduction reaction of NZVI/Ni/DM composite material with Fenton oxidation reaction to construct diatomite supported Fe-Ni nanoparticles-Fenton method（NZVI/Ni/DM-Fenton）reaction system.The results showed that the pH is controlled within the range of 1-3,the reaction time is 240min,the shaker speed is 150r/min,the dosage of the material is 3g/L,and the dosage of hydrogen peroxide is 800mmol/L.The treated waste water has a COD removal rate of59.17%and NH₃-N removal rate of 89.43.BOD₅/COD increased from 0.13 to 0.45,and the biodegradability was significantly improved.The reaction of NZVI/Ni/DM-Fenton to treat folic acid production waste water conforms to quasi-second order dynamics.